Cognitive Decline & Healthy Aging

5-HTP is the immediate serotonin precursor and crosses the blood–brain barrier, directly augmenting central serotonin synthesis. Age-related declines in serotonergic function have been linked to reduced prefrontal activity, memory impairment, and increased risk of mild cognitive impairment. A 2025 randomized controlled trial in older adults found that 100 mg/day of 5-HTP for 12 weeks produced a statistically significant improvement in global cognitive scores and reduced depressive symptoms. Evidence is promising but currently limited to a single small pilot RCT; larger, longer trials are needed.

Acetyl-L-Carnitine (ALC) has been investigated in multiple randomized controlled trials and systematic reviews for cognitive decline and aging-related dementia, primarily Alzheimer's disease. Early studies and a 2003 meta-analysis suggested modest benefits on clinical and psychometric scales, but a concurrent Cochrane systematic review found insufficient evidence to recommend clinical use, and larger subsequent trials did not consistently support the earlier positive findings. Serum ALC levels decline progressively from healthy aging through mild cognitive impairment to Alzheimer's disease, supporting a biological rationale. Overall, the evidence base is clinically mixed and further well-designed trials are needed.

Adzuki bean extract has been shown to inhibit amyloid-β42 aggregation in vitro and delay cognitive impairment in Alzheimer's Drosophila models. A mouse study found adzuki bean reversed HFD-induced cognitive impairment and memory deficits. Acetylcholinesterase inhibitory activity has also been identified in Australian adzuki bean phenolics.

AKG is a TCA cycle intermediate that declines ~10-fold between ages 40 and 80 in humans. A human study in 42 adults (mean age 64) supplementing with Ca-AKG for ~7 months reported an average 8-year reduction in DNA methylation biological age. Preclinical evidence shows Ca-AKG rescues synaptic plasticity deficits in Alzheimer's mouse models and improves cognitive function via mTOR pathway modulation.

A. muciniphila abundance declines with aging and has been inversely associated with neurodegenerative disease markers and cognitive decline in multiple animal models. It mitigated cognitive deficits and amyloid pathology in Alzheimer's disease mouse models, prevented cognitive impairment in sleep-deprived mice, and showed links to Parkinson's disease dementia in human gut microbiome studies. Mechanisms operate via the microbiota-gut-brain axis, neuroinflammation suppression, and SCFA-mediated epigenetic effects.

ALA shows emerging evidence for counteracting cognitive impairment associated with aging and neurodegeneration. RCTs in older adults show improvements in verbal fluency and sustained attention; preclinical data support neuroprotection against AD pathology.

Alpha-lipoic acid (ALA) has been studied clinically for cognitive decline and aging-related neurodegeneration, particularly in Alzheimer's disease (AD). Mechanistically, ALA is an antioxidant that crosses the blood-brain barrier, scavenges reactive oxygen species, and activates neuroprotective pathways. Clinical evidence is limited and mixed: a randomized pilot trial found that ALA combined with omega-3 fatty acids slowed cognitive and functional decline in AD patients over 12 months, while a small open-label study in cognitively normal elderly found no significant benefit. Larger, well-powered RCTs are still needed to establish efficacy.

Algal oil DHA has been directly tested in cognitive aging RCTs. The MIDAS trial (900 mg algal DHA/day, n=485, 24 weeks) demonstrated significantly fewer paired associative learning errors in older adults with mild memory complaints. DHA levels are inversely associated with dementia risk in observational data, and algal DHA improves cognitive biomarkers in aging animal models.

A 6-month RCT in middle-aged to older adults found significant improvements in specific cognitive measures (visuospatial working memory, visual memory and learning, spatial planning) with 3 oz/day almond consumption. Animal studies support anti-amnesic and neuroprotective effects via antioxidant pathways. However, the same RCT found no overall significant group difference in composite cognitive scores.

DHA from anchovies is a primary structural component of brain neuronal membranes and is directly linked to cognitive function. Observational studies associate higher omega-3 intake with lower Alzheimer's biomarkers. A Nature Scientific Reports systematic review and dose-response meta-analysis confirmed omega-3 supplementation has positive effects on cognitive function, particularly in older adults.

Anemarrhena constituents, including timosaponin B-II, AIII, sarsasapogenin, and mangiferin, exhibit neuroprotective and anti-dementia effects in rodent models of Alzheimer's disease and vascular dementia. AChE inhibition, anti-amyloid activity, and reduction of neuroinflammatory cytokines are among the identified mechanisms.

Epidemiological evidence associates regular apple and flavonoid consumption with reduced risk of cognitive decline and neurodegenerative conditions. Apple polyphenols including quercetin have documented neuroprotective mechanisms including reduction of neuroinflammation, oxidative stress, and amyloid-beta accumulation.

Multiple human RCTs demonstrate that Aronia melanocarpa extract improves psychomotor speed, attention, and reaction time across young, middle-aged, and older adults, with effects associated with increased serum BDNF and improved cerebral blood flow. A 2025 RCT specifically in older adults at increased cognitive impairment risk (n=30, assessed via ASL-MRI) investigated effects on brain vascular function and cognitive performance.

The ashitaba compound DMC extends lifespan in yeast, worms, and flies and decelerates senescence in human cell cultures via autophagy induction (Nature Communications, 2019). Ashitaba also contains coumarins that enhance nerve growth factor (NGF) production in vitro. Preclinical neuroprotective effects include protection from demyelination and improved behavioral responses in mice.

Multiple randomized, double-blind, placebo-controlled trials in humans support Ashwagandha's ability to improve memory, executive function, attention, and information-processing speed, particularly in adults with mild cognitive impairment (MCI). A 2019 systematic review of five clinical studies confirmed improvements in cognitive tasks and reaction time. The active withanolide compounds appear to act via acetylcholinesterase inhibition, antioxidant activity, and inhibition of β-amyloid aggregation. Evidence is promising but comes primarily from small, short-duration trials; large-scale long-term studies are still needed.

Astaxanthin, a marine xanthophyll carotenoid, has human clinical trial evidence supporting modest improvements in memory and psychomotor performance in middle-aged and older adults. Its ability to cross the blood–brain barrier and act as a potent antioxidant and anti-inflammatory agent underpins its proposed neuroprotective mechanism. Evidence is promising but limited by small sample sizes and few large RCTs, with most strong mechanistic data still preclinical.

Astragalus activates telomerase and extends telomere length, opposing the cellular aging mechanism implicated in cognitive decline. A randomized double-blind trial (n=40, mean age 56) found an astragalus-containing formulation improved cognitive metrics (P300 latency, Rey's 15-word test) and antioxidant capacity over 6 months. Preclinical evidence shows astragalus constituents inhibit β-amyloid aggregation, tau hyperphosphorylation, and neuroinflammation.

Bacopa monnieri (brahmi) has human clinical trial evidence supporting modest improvements in memory and cognitive performance in aging adults. Multiple randomized, double-blind, placebo-controlled trials and systematic reviews demonstrate benefits primarily in delayed word recall and processing speed. Evidence quality is limited by small sample sizes and trial heterogeneity, but the direction of effect is consistent across studies.

Bacosides — the principal triterpenoid saponins of Bacopa monnieri — have demonstrated cognitive-supporting effects in multiple randomized, double-blind, placebo-controlled human trials, particularly in older adults. Their mechanisms include antioxidant activity in key brain regions, cholinergic modulation, anti-neuroinflammatory effects, and promotion of synaptic repair. A 2012 systematic review of nine RCTs found eight reported improvements in memory, attention, and cognition. Typical clinical dosing studied is 300 mg/day of standardized extract (≥45–55% bacosides) for 12 weeks.

Berberine from barberry has been studied for neuroprotective effects relevant to cognitive aging, including reduction of amyloid plaque formation, oxidative stress, and neuroinflammation. Multiple preclinical studies support these mechanisms; human trials are limited.

Icariin has been extensively studied in animal models of neurodegenerative disease and aging, demonstrating protection against cognitive decline through multiple mechanisms including amyloid-beta reduction, tau dephosphorylation, BDNF upregulation, and anti-neuroinflammation. It also delays aging-associated neurological changes in rodents. No human cognitive aging trials have been published.

Holy basil has clinical evidence for cognitive benefit in stressed adults (n=158 RCT, 6 weeks) and healthy young men (n=40, 30 days), with improvements in memory and reaction time. Preclinically, basil polyphenols stimulate BDNF/NGF pathways, reduce neuroinflammation, and protect against neurodegenerative changes. Neuroprotective activity is documented across multiple PMC reviews.

Beetroot nitrate increases cerebral blood flow and may slow cognitive decline associated with aging by improving perfusion to regions most vulnerable to age-related hypoperfusion, including the prefrontal cortex. Evidence is preliminary, with mixed results from RCTs.

Benfotiamine targets multiple hallmarks of brain aging including impaired glucose metabolism, AGE accumulation, oxidative stress, and neuroinflammation. A phase IIa RCT in MCI/mild AD patients showed 77% lower CDR worsening (p=0.034) and significant AGE reduction. A large Phase 2A/2B national trial (BenfoTeam, n=406) is currently ongoing.

Berberine has demonstrated consistent neuroprotective effects in preclinical Alzheimer's disease models, reducing amyloid-beta deposition, tau phosphorylation, and neuroinflammation. Indirect clinical evidence exists through BBR's management of metabolic risk factors (diabetes, dyslipidemia, hypertension) that contribute to cognitive decline. Direct human cognitive endpoint trials are currently absent.

Dietary intake of total tocopherols including beta and delta forms has been associated with reduced risk of Alzheimer's disease and slower cognitive decline in prospective cohort studies. Brain gamma-tocopherol concentrations specifically correlate with lower amyloid burden and fewer neurofibrillary tangles. The Chicago Health and Aging Project found that higher dietary tocopherol intake (including individual forms) reduced 4-year Alzheimer's disease incidence.

Carnosine levels are markedly reduced in aging brains and in Alzheimer's disease. A systematic review with meta-analysis of 5 clinical studies found that carnosine/anserine supplementation (1 g/day for 12 weeks) improved global cognitive function in elderly subjects and those with mild cognitive impairment. BA, as the rate-limiting precursor to carnosine, represents an indirect means to support this pathway, with direct RCT evidence in older adults showing cognitive improvements particularly in those with below-normal baseline function.

Long-term beta-carotene supplementation (average 18 years in the Physicians' Health Study) was associated with significantly better cognitive performance and verbal memory in men versus placebo. Cross-sectional NHANES data confirm higher dietary beta-carotene is associated with lower risk of cognitive decline on multiple standardized tests. Duration of exposure appears critical, with short-term supplementation showing no benefit.

Elevated homocysteine — which betaine robustly lowers — is a recognized risk factor for cognitive decline, dementia, and Alzheimer's disease. Betaine is FDA-approved for homocystinuria, a disorder with severe neurological sequelae when untreated. One-carbon metabolism compounds including betaine are associated with epigenetic aging biomarkers in NHANES cohort data. Preclinical literature reports beneficial effects of betaine in Alzheimer's and Parkinson's disease models, though direct large human RCTs in aging populations are lacking.

An RCT in 60 healthy older adults found B. longum BB68S improved total cognitive function scores significantly after 8 weeks. B. longum is the most detected Bifidobacterium species from newborns to centenarians. Preclinical data show B. longum reduces amyloid pathology in Alzheimer's disease mouse models, with mechanistic links to neuroinflammation and BDNF.

Platycladus orientalis seed extract has been studied in Alzheimer's disease animal models and C. elegans nematode models, showing reduction of amyloid-beta plaque deposition, improved memory performance, and neuroprotection in 5xFAD transgenic mice. These preclinical findings support TCM's classical claim that biota seed 'benefits intelligence and prevents cognitive decline.'

A placebo-controlled trial in healthy elderly men (≥55 years; 500 mg N. sativa twice daily for 9 weeks) showed significant improvements in memory, attention, and cognition. TQ prevents hippocampal pyramidal cell loss, inhibits acetylcholinesterase, and reduces neuroinflammation relevant to age-related cognitive decline.

A 2023 comprehensive review in Aging and Disease (PMC) documents that piperine and other black pepper bioactive compounds show neuroprotective effects across multiple age-related neurological disorder models including Alzheimer's, Parkinson's, and Huntington's disease. Evidence is predominantly preclinical but mechanistically robust.

Epidemiological data and mechanistic research link habitual black tea consumption with preservation of cognitive function in aging. Theaflavins have demonstrated neuroprotective effects in aging mouse models by restoring gut microbial diversity and reducing neuroinflammation. Caffeine and L-theanine provide acute cognitive support across life stages.

Blackberry phenolics demonstrate neuroprotective effects in cell studies, including reducing neuronal ROS, modulating glutathione levels, and inhibiting apoptotic caspases in oxidatively challenged neuronal cells. Berry anthocyanins broadly are associated with improved cognitive and motor performance in aging animal models, and human longitudinal data associate berry consumption with slower cognitive decline.

Blueberries have meaningful human clinical evidence supporting their role in attenuating cognitive decline and supporting healthy brain aging, primarily driven by their high anthocyanin content. Multiple randomized controlled trials (RCTs) in older adults with mild cognitive impairment (MCI) or subjective cognitive decline have shown improvements in episodic memory, processing speed, and executive function. A 2025 meta-analysis of nine RCTs found a statistically significant improvement in episodic memory (SMD = 0.34) in elderly individuals with MCI or subjective cognitive decline. Epidemiological data further support these findings, with large longitudinal studies associating greater blueberry intake with slower rates of cognitive aging.

Observational data show decreased plasma boron is associated with increased Alzheimer's disease severity and cognitive decline in amnestic MCI patients (Lin et al., 2021). Reduced plasma boron was also found in APOE ε4 carriers (a major AD genetic risk factor). Experimental boron deprivation in older adults impaired multiple cognitive domains including memory, attention, and psychomotor function.

Multiple pilot RCTs show Boswellia extracts can mitigate cognitive decline in aging and neurological injury contexts. Neuroprotective mechanisms include anti-neuroinflammatory activity, antioxidant Nrf2 activation, BDNF upregulation, and possible AChE inhibition. Effects are modest but replicated across several small trials.

Bovine liver's B12, folate, choline, copper, and niacin all have documented relationships with age-related cognitive decline. B12 and folate reduce homocysteine, a neurotoxic amino acid associated with dementia risk. Choline supports phosphatidylcholine and acetylcholine in aging brains. Selenium decline with aging is associated with poorer cognitive outcomes.

Sulforaphane from broccoli crosses the blood-brain barrier, activates Nrf2 in neural tissue, reduces neuroinflammation, and supports BDNF (brain-derived neurotrophic factor). A 2025 PubMed review of 84 sulforaphane clinical trials identified neuroprotective effects as documented outcomes. Animal and early human data support a role in preventing age-related cognitive decline.

Butyrate shows promise as a neuroprotective agent in Alzheimer's disease and age-related cognitive decline via HDAC inhibition, neuroinflammation suppression, mitochondrial support, and blood-brain barrier maintenance. Evidence is primarily preclinical; human clinical trials are in early stages.

C. crista leaf aqueous extract demonstrated anti-amyloidogenic properties—inhibiting Aβ aggregation and disaggregating preformed fibrils—in vitro, directly relevant to Alzheimer's disease. Seed kernel extracts showed nootropic activity in scopolamine-induced amnesia models. Phytochemical profiling confirmed inhibition of both cholinesterase and β-amyloid aggregation.

Multiple prospective epidemiological studies and systematic reviews associate moderate caffeine intake (~200–300 mg/day) with a reduced risk of cognitive decline, mild cognitive impairment (MCI), and Alzheimer's disease (AD), though results are mixed and no randomized controlled trials exist. Caffeine's primary mechanism is antagonism of adenosine A2A receptors, which modulates neuroinflammation and reduces amyloid-beta burden in preclinical models. The evidence is promising but not yet conclusive enough to support a public health recommendation.

DHA and EPA from calamari oil support neuroprotection during aging through anti-inflammatory and membrane-stabilizing mechanisms. Multiple RCTs and meta-analyses show omega-3s help maintain cognitive function in aging populations, with the strongest evidence in mild cognitive impairment. A consistent finding across prospective studies is that higher fish intake is associated with less cognitive decline.

In Alzheimer's disease the brain develops glucose hypometabolism; ketones derived from caprylic acid provide an alternative fuel. Small human trials of MCT formulas containing caprylic acid show improvements in cognitive assessment scores, particularly in APOE4-negative patients. Evidence is promising but limited to small, short studies.

Observational studies link higher serum beta-carotene to reduced risk of cognitive decline, especially in genetically susceptible individuals (APOE ε4 carriers). Serum carotenoids show inverse associations with pro-inflammatory cytokines linked to neuroinflammation. Carotenoids are noted as important for infant cognitive development via breast milk.

BCP improved working memory and reduced circulating pro-inflammatory cytokines in aged mice via CB2 activation. Multiple studies link its anti-neuroinflammatory effects to protection against Alzheimer's-like pathology and age-related cognitive decline.

A human clinical study identified activation of the olfactory cortex of the brain as a measurable effect of cinnamon/cassia, and preclinical studies show C. cassia exerts neuroprotective effects in hippocampal tissue. Animal studies demonstrate reduction in neuroinflammation and restoration of blood-brain barrier integrity with C. cassia treatment.

Mitochondria-targeted catalase overexpression in aged mice improves neurovascular coupling and cerebral blood flow, protecting against age-related cognitive decline. Catalase glycation in Alzheimer's disease and aging accelerates neuronal degeneration and impairs mitochondrial homeostasis.

Catechins are well-evidenced for slowing age-related cognitive decline through antioxidant neuroprotection, anti-neuroinflammatory mechanisms, amyloid-beta inhibition, and BDNF upregulation. A Japanese RCT in adults with self-reported cognitive decline found 336.4 mg/day catechins significantly improved cognitive function. Both Alzheimer's and age-related cognitive decline have been investigated.

Sulforaphane from cauliflower activates Nrf2 neuroprotection, inhibits NF-κB neuroinflammation, and protects mitochondrial function—mechanisms relevant to Alzheimer's and Parkinson's disease. Choline in cauliflower supports acetylcholine synthesis and neuronal membrane integrity. EBSCO research notes neuroprotective potential of SFN.

Chen Pi nobiletin and tangeretin exhibit multi-target neuroprotective activity against Alzheimer's and Parkinson's disease pathology in preclinical models, including reduction of Aβ accumulation, tau hyperphosphorylation, neuroinflammation, and oxidative stress. All evidence is currently preclinical.

RCTs in older and middle-aged adults show tart cherry polyphenols improve memory, attention, and mental fatigue over 12 weeks. Mechanisms include blood-pressure lowering, antioxidant protection, anti-neuroinflammation, and direct crossing of the blood-brain barrier. Epidemiological data link anthocyanin intake to reduced Alzheimer's risk.

Danshen components, particularly tanshinone IIA, have demonstrated multi-modal neuroprotective effects relevant to cognitive aging and Alzheimer's disease, including Aβ clearance enhancement, acetylcholinesterase inhibition, neuroinflammation suppression, and hippocampal neuroprotection. The Chinese Pharmacopoeia lists Fufang Danshen preparations for Alzheimer's disease.

Chokeberry anthocyanins show neuroprotective activity in animal models relevant to Alzheimer's-type cognitive decline, including protection against amyloid-β toxicity. A human RCT examined chokeberry extract supplementation on cognitive performance and vascular function in healthy middle-aged adults. Evidence base is primarily animal model data with limited but existing human trial data.

Multiple human observational cohort studies and mechanistic research support a link between adequate choline intake and reduced risk of age-related cognitive decline. Choline serves as the primary dietary precursor to the neurotransmitter acetylcholine, whose loss is directly implicated in Alzheimer's disease and memory deficits. Evidence is strongest for cohort associations; large-scale RCT confirmation in older populations remains limited.

Chrysin protects against cognitive decline in aging animal models by preserving hippocampal neurogenesis, reducing neuronal apoptosis via antioxidant and anti-inflammatory mechanisms, and upregulating BDNF. Preclinical evidence spans D-galactose aging models, cerebral ischemia, and models of Alzheimer's-type and Parkinson's-type neurodegeneration.

Cinnamon extract inhibits amyloid-beta oligomerization, tau aggregation, and neuroinflammation in Alzheimer's disease animal models. A systematic review of 40 studies found broad support for cognitive improvement across preclinical models, with two clinical studies included. Human clinical evidence remains limited, but mechanistic plausibility is strong.

Citicoline (CDP-choline) is a naturally occurring intermediate in phosphatidylcholine biosynthesis that has been studied in multiple clinical trials for age-related cognitive decline, mild cognitive impairment (MCI), and dementia. Human evidence shows benefits in memory and behavior, particularly in individuals who already exhibit some degree of cognitive impairment, though overall study quality remains limited. A 2023 meta-analysis and a Cochrane review both identified positive signals alongside methodological concerns and possible publication bias. Typical clinical doses range from 500 mg/day to 1 g/day.

The COSMOS trial tested cocoa extract (500 mg/day flavanols) in 21,442 older adults over 3.6 years specifically targeting cognitive decline as a major goal. Cocoa flavanols improved cognitive processing speed in elderly RCTs. COSMOS also reduced CVD mortality by 27% and reduced the inflammaging marker hs-CRP by 8.4% annually.

Coconut oil provides MCTs metabolized to ketones, an alternative brain fuel when glucose metabolism declines with age and in Alzheimer's disease. A systematic review and meta-analysis found MCTs in coconut oil may improve cognitive abilities and potentially slow AD progression. Short-term cognitive benefits are documented in some RCTs, but evidence is classified as low quality overall.

MCTs from coconut oil are converted to ketone bodies, which provide an alternative brain fuel bypassing impaired glucose metabolism in Alzheimer's disease and cognitive aging. Multiple human studies of MCT oil have reported improvements in memory and cognition in mild cognitive impairment and Alzheimer's, and a 2025 Frontiers in Nutrition preclinical study found coconut-derived MCTs reduced amyloid-β, neuroinflammation, and memory deficits in an AD mouse model.

MCTs from coconut oil raise plasma ketone bodies, providing an alternative fuel for glucose-deprived neurons in aging and Alzheimer's disease. A 2024 meta-analysis found coconut oil significantly improved cognitive scores in AD patients vs. controls (p<0.05). A longest-duration RCT to date found 80% of participants had cognitive stabilization or improvement with continuous MCT oil over 9–11 months.

DHA is the predominant omega-3 in the brain and its concentration declines with aging. A 2022 review of 33 studies found omega-3 supplementation may protect against cognitive decline in healthy individuals without preexisting dementia. Evidence in established Alzheimer's disease is less consistent.

Coffee cherry extract has been specifically studied in older adults with mild cognitive decline in published RCTs. A 28-day RCT in 71 older adults with mild cognitive decline found CCE improved reaction time from the first week, persisting throughout the study. A neurophysiological pilot RCT in older adults with subjective cognitive impairment found CCE produced measurable neurofunctional changes in brain structures supporting cognition.

Copper homeostasis is deeply implicated in cognitive aging and neurodegeneration. Both deficiency (impairing myelination, neurotransmission, and energy) and excess (promoting amyloid-β aggregation and oxidative neuronal damage) are associated with cognitive decline. Low-normal serum copper correlates with cognitive impairment in older non-demented adults.

CoQ10 has been investigated in human clinical trials for its potential to support cognitive function and counteract age-related cognitive decline, primarily through its roles as a mitochondrial antioxidant and ATP-production facilitator. Endogenous CoQ10 levels decline with age, and low plasma CoQ10 has been associated with poorer cognitive and executive function in older adults. A 2025 review of 8 human RCTs found mixed results: roughly half showed benefit on cognition while the other half reported no significant improvement. Current evidence is preliminary and insufficient to support CoQ10 as a standard anti-cognitive-decline therapy.

Cordyceps militaris has demonstrated neuroprotective and cognitive-preserving effects in multiple animal models, including ischemia-induced neuronal death and Aβ1-42-induced Alzheimer's disease. Cordyceps polypeptides improve learning and memory by increasing cerebral blood flow and neurotransmitter function. Clinical evidence in elderly patients with chronic fatigue suggests improvement in memory and cognitive symptoms.

Creatine supplementation has been studied in the context of age-related cognitive decline, with a 2026 systematic review finding positive associations with memory and attention in older adults in 83% of included studies. A 2025 pilot trial in Alzheimer's disease patients demonstrated feasibility, increased brain creatine levels, and improvements across multiple cognitive composites.

Growing evidence supports creatine monohydrate as a strategy to attenuate cognitive decline with aging, with 83% of reviewed studies reporting positive associations between creatine and cognition in older adults. It also has investigational pilot-trial data in Alzheimer's disease and preclinical evidence of reducing amyloid-beta pathology.

Curcumin, the primary polyphenol from Curcuma longa, has been studied in multiple human RCTs for age-related cognitive decline, with some showing domain-specific benefits (particularly working memory in healthy older adults) but inconsistent results overall. A 2025 meta-analysis of 10 RCTs found no significant effect on global cognition (SMD = 0.14), while preclinical animal models show strong, consistent benefit. Poor oral bioavailability of standard curcumin formulations is widely cited as a key limiting factor, and enhanced-bioavailability preparations have produced more positive results in short-term trials. Evidence is promising but not yet conclusive.

D-alpha tocopherol at 2,000 IU/day has moderate-quality RCT evidence for slowing functional decline in established Alzheimer's disease, but does not prevent cognitive decline in healthy aging or progression from MCI to dementia. Epidemiological data support dietary vitamin E (as mixed tocopherols) but not α-tocopherol supplements alone for AD prevention.

Preclinical studies show daidzin has memory-enhancing, neuroprotective, anxiolytic, and antiepileptic CNS effects in animal models. Its phytoestrogenic activity and antioxidant properties are also proposed to support cognitive aging. Evidence is entirely preclinical; human studies are lacking.

DHA is the principal omega-3 fatty acid concentrated in the brain and is supported by multiple human clinical trials and systematic reviews for its role in cognitive aging. Evidence is strongest for early-stage cognitive decline and age-related cognitive decline, while benefits in established Alzheimer's disease are not demonstrated. Observational data consistently link higher DHA levels with reduced dementia risk, though RCT results remain mixed depending on disease stage and population.

Declining DHEA and DHEAS levels with aging have been implicated in cognitive decline. DHEAS modulates GABA-A, NMDA, and sigma-1 receptors in the brain and protects the hippocampus from glucocorticoid-induced damage. Despite promising preclinical data and correlational human evidence, RCTs in healthy older adults have not consistently demonstrated cognitive improvement with DHEA supplementation.

DMAE (via its derivative centrophenoxine) has been studied in elderly populations and dementia patients for cognitive decline. A large RCT of 242 patients with mild cognitive impairment taking DMAE for 24 weeks found no significant benefit over placebo for memory, executive function, or attention. Older small studies in senile dementia patients showed partial and inconsistent results. Centrophenoxine evidence in healthy elderly is limited and inconsistent, though animal data show reductions in lipofuscin accumulation.

DHA is the dominant structural omega-3 in the brain and is inversely associated with cognitive decline in observational studies. Multiple clinical trials in adults with mild cognitive impairment show variable but generally positive effects on episodic memory and attention. Trial data for Alzheimer's disease prevention have been largely negative at conventional doses, with bioavailability to the brain as a limiting factor.

DPA supplementation in aged rats attenuated hippocampal microglial activation and oxidative stress—the primary drivers of synaptic decline—improving spatial learning and long-term potentiation. DPA is also a structural omega-3 incorporated into neural membranes and can serve as a source of EPA and DHA in brain tissue. These preclinical findings support DPA's role in protecting against age-related cognitive decline.

EGCG, the primary polyphenol in green tea, has demonstrated neuroprotective mechanisms in preclinical models including antioxidant activity, inhibition of amyloid-beta aggregation, and tau phosphorylation reduction. Human clinical trials exist but are limited in number and scope: the most positive results come from Down syndrome populations, while trials in healthy adults and other neurological conditions show minimal or no benefit. No long-term RCT has yet confirmed that EGCG alone protects against cognitive decline or dementia in the general aging population.

Egg yolk choline, as the acetylcholine precursor, may slow age-related cognitive decline; a small RCT in older Japanese adults found 300 mg/day egg yolk choline improved verbal memory over 12 weeks. Observational cohort data further associate higher egg consumption with better overall cognitive function in aging populations.

EPA is associated with preservation of cognitive function in aging populations via cerebrovascular protection, anti-neuroinflammatory actions, and mitochondrial quality maintenance in neural and skeletal tissue. Observational data link higher EPA status to better MMSE scores in CAD patients, and EPA uniquely attenuates age-related mitochondrial decline in animal models.

Eleuthero has documented neuroprotective effects in Alzheimer's, Parkinson's, and aging models, reducing amyloid-beta, protecting dopaminergic neurons, and improving hippocampal plasticity. A clinical study in elderly hypertensive patients found modest cognitive improvement. Traditional use in TCM and Russian medicine emphasizes longevity and vitality.

EPA (eicosapentaenoic acid) has a scientifically documented but nuanced relationship with cognitive decline and healthy aging. Observational evidence, including a large meta-analysis of 48 longitudinal studies (103,651 participants), links higher EPA dietary intake and blood levels to reduced risk of cognitive decline and dementia. However, randomized controlled trials show mixed results, with effects varying by dose, baseline EPA status, and whether EPA is studied in isolation from DHA. Anti-inflammatory and neuroprotective mechanisms are biologically plausible and well-documented in preclinical research.

Eucommia extracts demonstrate neuroprotective activity against Alzheimer's and age-related cognitive decline in preclinical models, suppressing AChE activity, reducing Aβ deposition, and enhancing cholinergic signaling. These are distinct from its Parkinson's-specific effects and overlap with healthy brain aging.

Ferulic acid inhibits β-amyloid (Aβ) aggregation and plaque deposition, reduces neuroinflammation and oxidative stress, and improves brain capillary function in Alzheimer's disease models. A multicenter, randomized, double-blind clinical study of Feru-guard (a FA-containing supplement) in MCI patients aged 65–85 reported benefits on cognitive outcomes, representing the strongest current clinical evidence.

Fisetin, a naturally occurring flavonoid found in strawberries and other fruits, has documented preclinical evidence supporting neuroprotection and mitigation of age-related cognitive decline. It operates primarily through senolytic, antioxidant, and anti-inflammatory mechanisms. Human clinical trials are underway but peer-reviewed cognitive outcome data in humans remain limited, so the evidence base is currently preclinical with emerging clinical translation.

Observational evidence consistently links higher omega-3 status with lower risk of cognitive decline and dementia. DHA is a critical structural component of synaptic membranes, and fish oil may delay brain atrophy in aging. RCT evidence in cognitively healthy older adults has been largely neutral for preventing decline; benefits are more apparent in those with existing MCI or low baseline omega-3 status.

FMN supplementation has been shown in preclinical models to suppress amyloid-beta toxicity, modulate microglial neuroinflammation, and improve cognitive outcomes. Low riboflavin/FMN levels have been observed in dementia patients. Clinical evidence is preliminary but supports a mechanistic role for FMN in cognitive aging via antioxidant, anti-inflammatory, and homocysteine-lowering pathways.

ALA omega-3 from flaxseed is associated with reduced risk of cognitive decline in observational studies, and flaxseed oil prevented cognitive and motor impairment in an animal model of hepatic encephalopathy. Human RCT data specifically on cognitive outcomes with flaxseed are limited but mechanistic evidence is supportive.

Serum and CSF folate concentrations decline with age, while homocysteine rises, and low folate status is associated with mild cognitive impairment and dementia in population-based studies. Folic acid supplementation reduces plasma homocysteine and inflammatory markers in older adults, and a systematic review found positive effects on cognitive function in elderly individuals with mild cognitive impairment. However, consistent evidence that supplementation improves cognition or slows decline in cognitively healthy older adults is lacking.

Observational and interventional evidence links folate status to cognitive function in aging, with elevated homocysteine (reflecting folate insufficiency) doubling dementia risk in community cohort studies. Open studies specifically using folinic acid in folate-deficient elderly subjects reported striking improvements in mood and cognition. Folate supports cognitive aging through homocysteine lowering, methylation support, and neuroprotection.

Neuroprotective and anti-aging properties of Forsythia suspensa have been documented in preclinical studies relevant to Alzheimer's disease, Parkinson's disease, and cognitive aging. Forsythia leaves and flowers show significant anti-aging properties in vitro. Forsythoside A modulates neurodegenerative signaling pathways. Evidence is from animal/in vitro studies; no human trials have been conducted.

Multiple preclinical studies show Poria cocos polysaccharides and essential oils protect against Alzheimer's-model cognitive decline via AChE inhibition, hippocampal neuroprotection, reduction of oxidative stress, and MAPK/NF-κB pathway suppression. Pachymic acid is noted for maintaining cognitive homeostasis. Traditional TCM uses Fu Ling for amnesia, dementia, and longevity.

Fulvic acid inhibits tau fibril aggregation in vitro, a hallmark of Alzheimer's-type neurodegeneration. A 2025 systematic review found promising neuroprotective potential. Traditional use as a cognitive rejuvenator is established in Ayurveda.

In post-mortem human brain tissue from the Rush Memory and Aging Project, higher γT brain concentrations were significantly associated with lower amyloid load and lower neurofibrillary tangle severity. Dietary γT intake was inversely associated with incident Alzheimer's disease and cognitive decline in prospective cohort studies. Clinical trials specifically on γT supplementation for cognition are lacking.

Ganoderma lucidum spore extract significantly prevented learning and memory impairment in a rat Alzheimer's disease model via neuroinflammation suppression. A Cochrane-style systematic review protocol for human RCTs on the cognitive-impairment continuum has been formally registered.

Gardeniae Fructus is prescribed in TCM for brain aging and age-related diseases, and is supported by preclinical evidence for neuroprotection in Alzheimer's and Parkinson's disease models. Geniposide, genipin, and crocin demonstrate activities addressing mitochondrial dysfunction, oxidative stress, apoptosis, and neuroinflammation relevant to cognitive aging.

Gardenia jasminoides extracts (crocin-rich GJ-4) protected against cognitive decline in APP/PS1 transgenic Alzheimer's disease mice over 12 weeks of oral treatment. Genipin and crocin also protect against age-related neurodegeneration via anti-inflammatory, antioxidant, and tau-phosphorylation-reducing mechanisms. Evidence is from animal models of neurodegeneration.

Aged garlic extract (AGE) has been associated with improved cerebral perfusion and cognitive outcomes in aging populations. S-allyl cysteine (SAC), a key AGE compound, demonstrates neuroprotective mechanisms including reduction of amyloid-beta toxicity, oxidative stress, and neuroinflammation in preclinical models. Human evidence includes observations of beneficial cerebral perfusion effects.

AGE's antioxidant components (SAC, SAMC) protect neurons from oxidative damage. Preclinical and limited clinical evidence suggests garlic's anti-inflammatory and antioxidant properties may slow neurodegenerative processes. SAC has demonstrated neuroprotective properties in experimental models; direct large-scale human RCT evidence for cognitive outcomes is limited.

GE and gastrodin have been extensively studied in Alzheimer's disease and vascular dementia animal models, demonstrating reversal of memory dysfunction, amyloid reduction, and neuroprotection. Chinese clinical trials for vascular dementia have used gastrodin with positive cognitive outcomes.

Soy isoflavone interventions including genistein have improved certain cognitive functions in clinical studies, and genistein has shown neuroprotective activity in preclinical models. The Alzheimer's Research & Prevention Foundation's evidence review notes improvements in some cognitive domains, though no RCTs have tested genistein alone specifically for age-related cognitive decline.

Ginkgo biloba extract (EGb 761) has been extensively studied in human clinical trials for cognitive decline and healthy aging, making it one of the most researched botanical supplements in this domain. Evidence is mixed: large RCTs found no benefit for preventing dementia or slowing cognitive decline in cognitively normal older adults, while shorter RCTs at 240 mg/day show modest improvements in cognition and neuropsychiatric symptoms in mild cognitive impairment (MCI). An overview of ten systematic reviews concluded there is clear evidence supporting efficacy in MCI and dementia treatment, but the prevention question remains unresolved.

There is human clinical evidence—from randomized controlled trials and multiple systematic reviews—supporting Panax ginseng's modest benefit on memory and cognition, particularly in individuals with mild cognitive impairment (MCI) or Alzheimer's disease (AD). A 2024 meta-analysis of 15 RCTs found a statistically significant effect on memory improvement, especially at higher doses. However, a Cochrane review concluded that convincing evidence for a generalizable cognitive-enhancing effect is still lacking, and overall clinical evidence quality remains heterogeneous. Ginseng has also been used in traditional East Asian medicine for thousands of years to address aging and memory impairment.

Ginsenosides, the active triterpenoid saponins of Panax ginseng, have demonstrated neuroprotective properties in preclinical models of Alzheimer's disease and age-related cognitive decline, and a small body of clinical trials in AD patients has shown improvements in ADAS-cog and MMSE scores. However, existing human trials are limited in size and methodological quality, making definitive conclusions premature. Traditional Chinese medicine has long used ginseng root to address memory and cognitive complaints in aging.

Animal studies show G. littoralis extract promotes hippocampal neurogenesis, reverses scopolamine-induced cognitive impairment via BDNF/CREB upregulation, and protects neurons from ischemic injury. These neurobiological effects are directly relevant to cognitive aging mechanisms.

A 36-week pilot RCT of GlyNAC in older adults improved cognitive function alongside restoration of brain-relevant metabolic defects including glutathione deficiency, oxidative stress, mitochondrial dysfunction, and inflammation. Animal studies with GlyNAC reversed age-associated cognitive decline by restoring brain glutathione and neurotrophic factors. Glycine as a co-agonist at NMDA receptors also directly modulates synaptic plasticity relevant to memory and cognition.

LBP has demonstrated neuroprotective effects against Alzheimer's disease pathology in animal models, inhibiting amyloid-beta production, reducing neuroinflammation, and improving spatial memory. A pilot study in elderly participants consuming goji powder reported enhanced memory retention scores. Reviews highlight LBP as a promising candidate for neurodegenerative disease prevention.

Clinical studies support Gotu Kola's role as a neuroprotectant relevant to healthy cognitive aging. Evidence includes improved cognition in MCI patients, post-stroke patients, and healthy elderly subjects. A systematic review of clinical trials confirmed working memory benefits, and preclinical data show hippocampal synaptic density enhancement and protection from age-related neurodegeneration.

Glycerophosphocholine (GPC / alpha-GPC / choline alfoscerate) has substantial human clinical evidence supporting its use in cognitive decline associated with aging, Alzheimer's disease, vascular dementia, and mild cognitive impairment (MCI). It functions as a cholinergic precursor that crosses the blood–brain barrier, raising acetylcholine levels in brain regions critical to memory and learning. Multiple randomized controlled trials and a 2023 systematic review and meta-analysis (Journal of Alzheimer's Disease) confirm significant cognitive benefits in adult-onset dementia populations. Evidence for benefit in cognitively healthy individuals is limited and preliminary.

A 2024 double-blind RCT in 96 healthy older adults found 250 mg/day standardized Vitis vinifera extract significantly improved multiple cognitive domains within 14 days and continuing to 84 days. Resveratrol has been shown to penetrate the blood-brain barrier and affect AD biomarkers in a long-term RCT. Grape polyphenols also reduce amyloid-β aggregation in vitro and neuroinflammation in preclinical models of neurodegeneration.

A community-based, double-blind, placebo-controlled RCT in 71 elderly subjects with mild cognitive impairment (MCI) found that GSPE (320 mg/day for 6 months) favorably affected cognitive function assessed by MoCA. Animal models demonstrate OPCs reduce amyloid-beta aggregation and tau hyperphosphorylation relevant to Alzheimer's disease progression.

GMT has been systematically reviewed in a 2023 WHO-criteria monograph as a putative adaptogen for reducing the risk of age-related cognitive decline. Multiple human studies demonstrate improved cognitive performance, cerebral blood flow, and reduced anxiety in older adults. Preclinical data show amyloid-β inhibition in C. elegans and mouse AD models, providing neuroprotective mechanistic support.

Multiple prospective cohort studies and meta-analyses demonstrate that habitual green tea consumption is associated with reduced risk of dementia and cognitive decline in older adults. A 2025 longitudinal cohort study in 1,155 participants followed for up to 20 years found that 2–3 cups/day reduced the risk of significant cognitive decline by 44% (OR 0.56). A 2023 meta-analysis of 7 prospective cohort studies found tea consumption associated with a 29% reduced risk of all-cause dementia (RR=0.71).

Habitual guarana consumption in an elderly Amazonian population was associated with lower oxidative stress markers and lower prevalence of metabolic conditions that drive cognitive decline. In vitro studies demonstrate neuroprotective and antiaging properties. Guarana improved memory in a rat model of hyperlipidemia-associated cognitive impairment. A 2021 systematic review supports guarana for cancer-related fatigue in aging patients.

Hesperetin demonstrates neuroprotective and antioxidant properties in preclinical models relevant to cognitive aging. Its ability to reduce neuroinflammation and oxidative stress in neural tissue provides mechanistic support for healthy cognitive aging, though human clinical trial evidence is currently limited.

A limited number of clinical trials have shown hesperidin-enriched dietary supplements significantly improve cerebral blood flow, cognition, and memory performance in older adults. Preclinical data consistently show neuroprotection in Alzheimer's and aging-related models. Most human evidence derives from orange flavanone-enriched supplementation trials rather than pure hesperidin RCTs.

HMR reaches brain tissue after oral administration in animals and showed neuroprotective effects in a rodent Parkinson's disease model by slowing dopaminergic neuron degeneration and improving motor performance. Phytoestrogenic properties are linked in broader literature to cognitive aging; however, no human cognitive endpoint trials with HMRlignan exist.

Huperzine A is a natural acetylcholinesterase (AChE) inhibitor derived from the Chinese club moss Huperzia serrata, with documented human clinical trial evidence for improving cognitive function in Alzheimer's disease and vascular dementia. Multiple meta-analyses of randomized controlled trials show significant improvements on standardized cognitive scales (MMSE, WMS, HDS) versus placebo, though the quality of the underlying trials is generally rated as having a high risk of bias. No studies have yet tested whether it can prevent dementia or cognitive decline in healthy aging populations.

A 2025 double-blind RCT (n=100, PMC12719083) of a Boswellia serrata and Terminalia chebula combination in ageing adults demonstrated significant improvements in multiple cognitive domains and BDNF levels. Anti-inflammatory and antioxidant mechanisms protect neurons from age-related oxidative and inflammatory damage. Traditional Ayurvedic medicine classifies Boswellia as a rasayana (anti-ageing) herb.

Iodine deficiency contributes to accelerated cognitive decline across the lifespan, including in older adults. A 2025 cross-sectional NHANES study found associations between urinary iodine concentration and composite cognitive scores in older Americans. A 2025 editorial in a peer-reviewed journal calls for lifespan-based public health strategies linking iodine sufficiency to protection of cognitive well-being into older age. The relationship is modulated by thyroid hormone status.

Iron status has a dual, complex relationship with cognitive aging: both deficiency (impairing oxygen transport, myelination, and neurotransmitter synthesis) and excessive brain iron accumulation (promoting oxidative stress and interaction with amyloid and tau pathology) are associated with cognitive decline. MRI-based meta-analyses have found elevated iron in the basal ganglia of Alzheimer's disease patients is negatively associated with cognitive performance. In older adults, adequate but not excessive dietary iron intake correlates with better cognitive test performance.

A 2026 peer-reviewed ScienceDirect review identified jiaogulan as a neuroprotective agent targeting Alzheimer's disease, Parkinson's disease, and age-related cognitive decline via antioxidant, anti-inflammatory, neurogenic, and cholinesterase-inhibiting mechanisms. Preclinical models demonstrate protection of hippocampal and cortical neurons.

Jujube polysaccharides and jujuboside A have demonstrated neuroprotective and longevity-extending activity in C. elegans models via DAF-16/FOXO3A and SKN-1/Nrf2 pathways. Jujube extracts attenuate scopolamine-induced and D-galactose–induced cognitive deficits in rodents. TCM has classified jujube as a longevity and brain-tonic herb for millennia. Evidence is preclinical.

Kale's sulforaphane activates Nrf2 in the brain, upregulating neuroprotective antioxidant enzymes and showing promise against neurodegeneration in preclinical models of Alzheimer's, Parkinson's, and other conditions. Cohort data link dietary antioxidant vitamins and carotenoids (found abundantly in kale) to better cognitive trajectories over time. Evidence is primarily preclinical with emerging epidemiological support.

A proof-of-concept RCT explicitly designed for Alzheimer's implications found Zembrin improved executive function and cognitive flexibility in cognitively healthy middle-aged adults via the PDE4-cAMP-CREB pathway. Network pharmacology analyses have mapped kanna alkaloid targets onto Alzheimer's disease pathways. No trials have yet been conducted in people with cognitive impairment.

Resveratrol from knotweed crosses the blood-brain barrier and has been evaluated in Alzheimer's disease clinical trials. An umbrella review of systematic evidence found that resveratrol improved MMSE scores and FIM scores (p<0.05) and reduced ADAS-cog scores (p<0.001) in mild cognitive impairment. Resveratrol inhibits amyloid-beta aggregation and tau phosphorylation via SIRT1 activation.

A 2013 RCT (Konagai et al.; n=45 healthy elderly) found krill oil improved working memory and prefrontal cortex activation versus placebo. No dedicated human clinical trials testing krill oil for prevention of cognitive decline or dementia have been conducted. Multiple animal models confirm krill oil attenuates Alzheimer's-like pathology and aging-related cognitive impairment.

ALC has been studied across 16+ controlled trials for dementia and cognitive decline. A 2003 meta-analysis showed significant advantages on clinical and psychometric tests. A 2024 Mendelian randomization study found reduced ALC levels causally associated with adverse neurocognitive outcomes. Evidence suggests ALC may slow cognitive decline, particularly in Alzheimer's disease and secondary dementias.

Carnosine levels are significantly reduced in aging brain and in dementia patients. Human RCTs using anserine/carnosine formulas in elderly individuals demonstrate preservation of verbal memory and brain perfusion. A 2023 systematic review and meta-analysis confirmed potential therapeutic activity in age-related diseases including neurodegenerative disorders.

Aging-associated cognitive decline is mechanistically linked to glutathione deficiency in the brain, driving oxidative stress, mitochondrial dysfunction, and neuroinflammation. Human clinical trials with GlyNAC (GSH precursors) corrected brain GSH deficiency and significantly improved cognitive function in older adults over 24 weeks, with benefits reversing upon discontinuation.

GlyNAC supplementation in multiple clinical trials in older adults demonstrates significant improvements in cognitive function, including Montreal Cognitive Assessment (MoCA) scores, alongside reversal of oxidative stress, mitochondrial dysfunction, and inflammation that drive age-related cognitive decline. Glycine's role as an NMDA co-agonist further supports synaptic plasticity relevant to cognitive aging.

A Phase IIa randomized, double-blind, placebo-controlled trial of L-serine is underway in early Alzheimer's disease patients (NCT03062449), based on evidence that serine deficiency contributes to synaptic and neuronal dysfunction. In serine-deficiency disorders, early L-serine treatment prevents cognitive decline. However, no completed RCT yet demonstrates cognitive benefit in normal aging or sporadic Alzheimer's disease.

L-Theanine, an amino acid from green tea (Camellia sinensis), has been investigated in multiple human RCTs for cognitive support in middle-aged and older adults. Acute single-dose administration shows modest benefits for attention and working memory, but chronic supplementation trials have generally not demonstrated significant improvement over placebo on broad cognitive batteries. A notable exception involves L-theanine combined with green tea extract, which improved memory and attention in subjects with mild cognitive impairment (MCI) over 16 weeks. Overall, the evidence base is real but limited in size and consistency, with GRADE assessments rating certainty as low to very low.

RCTs of specific L. plantarum strains (OLL2712, C29-fermented soybean) show cognitive protection in older adults with declining memory. A systematic review identified L. plantarum as a complementary intervention for neurodegenerative symptomatology.

Lavender essential oil (linalool) has demonstrated neuroprotective effects against D-galactose and AlCl3-induced cognitive deficits in mice. A small human study of 17 elderly Alzheimer's patients found that aromatherapy with lavender, rosemary, lemon, and orange improved cognitive function. Preclinical data indicate lavender oil inhalation can reverse spatial memory loss in dementia models.

Lecithin/phosphatidylcholine research has specifically targeted age-related cognitive decline, with multiple RCTs and a Cochrane review addressing Alzheimer's disease, dementia, and subjective memory impairment. A 2025 multicenter RCT in Chinese older adults found lecithin protective against both memory deficits and muscle attenuation. Evidence is mixed but genuine clinical research exists.

Clinical evidence supports lemon balm for slowing cognitive decline in early Alzheimer's disease, with a landmark 2003 RCT showing significant cognitive improvement and reduced agitation. A 2020 study further confirmed safety and potential efficacy. The neuroprotective mechanism involves acetylcholinesterase inhibition, antioxidant defence, and anti-inflammatory activity.

Higher dietary intake of lignans has been associated with better cognitive performance in postmenopausal women in observational research. Lignans and their metabolites have demonstrated neuroprotective potential through antioxidant action and oxidative stress amelioration in the brain. A 2025 review of lignans identifies neuroprotective potential as an emerging area of research.

Lion's Mane (Hericium erinaceus) has human clinical trial evidence supporting modest improvements in cognitive function, particularly in older adults with mild cognitive impairment (MCI). Its bioactive compounds — hericenones (fruiting body) and erinacines (mycelium) — promote nerve growth factor (NGF) synthesis, a plausible neuroprotective mechanism. However, completed human trials are small and short, results are mixed across populations, and benefits appear to require ongoing supplementation. Larger, longer trials are still needed.

A landmark 2025 Nature study (Aron et al.) found significantly reduced lithium levels in prefrontal cortex of humans with MCI and Alzheimer's disease, and demonstrated that low-dose lithium orotate reversed memory loss in Alzheimer's mouse models. Epidemiological data and meta-analyses further link higher lithium exposure to lower dementia risk. A Phase 4 LATTICE RCT tested lithium in MCI, and a dedicated lithium orotate Alzheimer's trial (NCT07459959) is now underway.

Lotus seed constituents (neferine, proanthocyanidins) inhibit AChE, BChE, and BACE-1—enzymes central to Alzheimer's disease pathology—in preclinical models and improve memory in rodent amnesia models. No human trials for cognitive decline exist.

Lutein is the most abundant carotenoid in human brain tissue, and lower brain and plasma levels are associated with greater age-related cognitive decline. RCTs using fMRI demonstrate that lutein and zeaxanthin supplementation buffers cognitive decline in verbal learning tasks and enhances cerebral perfusion in older adults. Population-based studies across 4,000+ older adults confirm independent associations between higher plasma lutein and better global cognition, memory, and executive function.

Luteolin, a dietary flavone found in celery, parsley, and chamomile, has substantial preclinical evidence supporting neuroprotection and attenuation of cognitive decline via anti-inflammatory, antioxidant, and anti-amyloid mechanisms. It suppresses microglial activation and neuroinflammatory signaling pathways (NF-κB, MAPK) implicated in brain aging. Human clinical evidence is nascent — early-phase trials are underway or recently completed, but robust, published RCT results in aged or cognitively impaired populations are not yet available. The evidence base is currently strongest at the preclinical level, with clinical translation actively in progress.

Lychee seed polyphenols have shown neuroprotective effects in Alzheimer's disease and T2DM cognitive impairment animal models, reducing Aβ, Tau, and AGE accumulation in the hippocampus and preventing neuronal apoptosis. Lychee polyphenols may delay Alzheimer's progression through PKC pathway activation and insulin resistance improvement. Oligonol's systemic anti-aging effects (reduced inflammation, improved circulation, antioxidant defense) are also relevant to healthy brain aging.

Human epidemiological evidence from cross-sectional and longitudinal studies supports an association between higher lycopene status and maintained cognitive function in aging adults. Among 10 identified human studies, three of four examining cognition maintenance showed significant positive relationships. Preclinical studies robustly demonstrate lycopene's ability to reduce age-associated neuroinflammation, Aβ accumulation, and synaptic dysfunction.

Macadamia nuts contain tocotrienols and MUFAs that are associated with neuroprotection and reduced risk of cognitive decline. Epidemiological studies link elevated plasma tocotrienol levels to reduced odds of mild cognitive impairment and Alzheimer's disease. Oleic acid protects against neuronal oxidative stress in animal models. Human RCT evidence specifically for macadamia nuts and cognition is limited.

Magnesium plays a well-documented role in neurological function, and both low dietary intake and low serum magnesium are independently associated with greater risk of cognitive decline and dementia in epidemiological studies. A 2024 systematic review and meta-analysis found consistent U-shaped associations between serum magnesium and all-cause dementia, suggesting an optimal serum level near 0.85 mmol/L. The brain-penetrant form, magnesium L-threonate, has shown cognitive benefits in multiple small RCTs in older adults. Overall evidence is promising but robust long-term intervention trials remain limited.

Honokiol protects against beta-amyloid toxicity, reduces neuroinflammation, activates SIRT3, and promotes oligodendrocyte regeneration in preclinical Alzheimer's disease and cerebral ischemia models. Honokiol crosses the blood-brain barrier readily. PubMed reviews classify honokiol/magnolol as having therapeutic potential in cognitive disorders including Alzheimer's disease. No human cognitive-decline trials exist.

A 2026 18-week randomized, double-blind, placebo-controlled human trial in 47 healthy adults aged 60+ found daily maitake consumption significantly improved cognitive scores, particularly memory—the first controlled human evidence linking maitake to cognitive preservation. Animal models implicate antioxidant and NK-cell-mediated mechanisms.

Mangosteen pericarp reduced cognitive impairment and decreased phospho-tau in aging mice and triple-transgenic Alzheimer's model mice. Xanthones inhibit amyloid-beta deposition, tau hyperphosphorylation, and cholinergic dysfunction in AD models. A 24-week RCT in 114 schizophrenia patients examined cognitive outcomes with mangosteen pericarp extract. Evidence is primarily preclinical for Alzheimer's specifically.

Maqui delphinidins exhibit neuroprotective properties in cell models, protecting neurons from rotenone-induced damage (a Parkinson's model) and photoreceptor cells from oxidative apoptosis, with suggested neuroprotective effects beyond the retina. Reduction of postprandial glucose spikes—demonstrated in human trials—is also relevant, as chronic glycemic excursions associate with impaired cognitive function and accelerated neurodegeneration.

Multiple RCTs and meta-analyses indicate MCT supplementation can stabilize or modestly improve cognitive function in MCI and mild-to-moderate Alzheimer's disease by providing ketone bodies as an alternative brain fuel. Benefits appear largest in those with higher baseline cognitive function and in those receiving continuous rather than intermittent MCT supplementation.

Melatonin, an endogenous pineal hormone that declines with age, has been studied in clinical trials for its potential to slow cognitive decline in mild cognitive impairment (MCI) and Alzheimer's disease (AD). Evidence from multiple RCTs and meta-analyses suggests modest cognitive benefits, particularly in MCI patients and those with comorbid sleep disturbance, though results in more advanced dementia remain inconsistent. Its proposed mechanisms include antioxidant activity, inhibition of amyloid-beta aggregation, anti-tau effects, and circadian rhythm restoration. Larger, longer-duration trials are still needed to firmly establish efficacy and optimal dosing.

Observational and interventional evidence links vitamin B12 status—particularly MeCbl—to cognitive aging. B12 deficiency is associated with accelerated cognitive decline, brain atrophy, and elevated homocysteine. MeCbl is mechanistically implicated via myelin maintenance, methylation, and homocysteine clearance. RCT evidence is mixed but selected trials in high-risk groups show slowing of brain atrophy.

Silymarin shows neuroprotective effects in multiple preclinical models and emerging human data. Animal studies demonstrate suppression of amyloid-β plaque formation and improvement in cognitive performance. A small 2020 human trial in adults with mild cognitive impairment reported improvements in memory and attention after 6 months of milk thistle extract supplementation.

M. officinalis oligosaccharides (MOO) have been studied in multiple Alzheimer's disease animal models, demonstrating improved learning and memory, reduced amyloid-β toxicity, suppression of neuroinflammation, and activation of neuroprotective Nrf2/ARE antioxidant pathways. A dedicated 2022 Frontiers in Aging Neuroscience review summarises these neuroprotective mechanisms.

Morus extracts demonstrate neuroprotective properties in multiple preclinical models, reducing amyloid-β, improving memory, and modulating neuroinflammation. The 2025 meta-analysis linked mulberry's metabolic risk factor reduction to lower vascular dementia risk. Mechanistic evidence from preclinical models is robust, though human RCTs specifically targeting cognition are limited.

POEE has demonstrated neuroprotective and anti-amnesic effects in rodent aging and Alzheimer's disease models, with AChE inhibition in memory-relevant brain regions, reduction of amyloid-beta-related neuroglial degeneration, and upregulation of nerve growth factor. Elderly Amazonian communities have traditionally favored the plant for age-related cognitive complaints.

Mulberry-derived anthocyanins and polyphenols have shown neuroprotective and cognitive benefits in multiple animal models, including Alzheimer's disease and natural aging. A meta-analysis specifically assessed mulberry's modulation of metabolic risk factors contributing to vascular dementia. No direct human RCTs for cognitive outcomes have been published.

A 2025 randomized, double-blind, placebo-controlled trial (n=100, 120 days) of a TC + Boswellia serrata combination significantly improved multiple cognitive function measures and sleep quality in adults with subjective memory complaints. TC extract also prevented scopolamine-induced amnesia in mice via cholinergic modulation.

N-Acetyl Cysteine (NAC) has documented clinical and preclinical evidence supporting a role in mitigating age-related and dementia-associated cognitive decline, primarily through its function as a glutathione precursor that counters oxidative stress and neuroinflammation. Human trials testing NAC alone have yielded modest and inconsistent results, while combination nutraceutical formulations containing NAC have shown more consistent pro-cognitive benefits in Alzheimer's disease patients and older adults with mild cognitive impairment. The overall human evidence base remains preliminary, with no large-scale RCTs yet confirming NAC monotherapy for cognitive aging.

Naringin/naringenin demonstrate preclinical efficacy against cognitive decline in Alzheimer's and Parkinson's disease models, inhibiting acetylcholinesterase, clearing amyloid-β, reducing neuroinflammation, and protecting dopaminergic neurons. Broad pharmacological evidence across multiple neurological paradigms supports a role in cognitive healthy aging. No human cognitive aging trials have been published.

Nattokinase has been investigated for cognitive benefits through its fibrinolytic, amyloid-degrading, and neuroinflammatory pathways. The ICC-PACS RCT (2025/2026; n=88 completers; 8,000 FU/day for 6 months) in patients with asymptomatic intracranial/carotid stenosis found no significant improvement in global cognition (MoCA) but showed exploratory benefits in visuospatial function. Preclinical data in Alzheimer's models demonstrate NK reduces amyloid-beta plaques, restores BDNF signaling, and reduces neuroinflammatory markers.

Nicotinamide riboside (NR) is an orally bioavailable NAD+ precursor investigated for cognitive decline and healthy aging on the basis that NAD+ levels decline with age, impairing mitochondrial bioenergetics, DNA repair, and sirtuin-mediated cellular maintenance in the brain. Multiple completed randomized controlled trials in older adults with mild cognitive impairment or subjective cognitive decline confirm NR safely elevates NAD+ levels, though short-term trials (8–12 weeks) have not yet demonstrated significant improvement in cognitive test scores. Biomarker evidence from neuronal extracellular vesicles and preclinical Alzheimer's models is more encouraging, warranting larger and longer trials.

NMN (β-Nicotinamide Mononucleotide) is an NAD+ precursor whose supplementation is supported by mechanistic and preclinical evidence relevant to cognitive decline and healthy aging. NAD+ levels decline with age in the brain, contributing to neurodegeneration, axonal degeneration, and cognitive impairment. Preclinical models show NMN improves cerebrovascular function, reduces hippocampal synaptic disruption, and restores cognitive performance. Human clinical trials confirm NMN raises blood NAD+ levels and is well-tolerated, though direct cognitive benefit in humans remains to be definitively established.

Oat β-glucan's cardiometabolic benefits (LDL reduction, blood pressure modulation, glycemic control) address key vascular risk factors for cognitive decline. Direct evidence from an RCT shows reduced difficulty concentrating with OBG. Antioxidant avenanthramides provide neuroprotective potential.

OA protects against neuroinflammation-driven neurotoxicity and reverses scopolamine-induced memory impairment in rodents via TrkB/BDNF-ERK1/2-CREB pathway activation. It also reduces Alzheimer's-related amyloid-beta-driven astrocyte toxicity and cognitive decline markers.

Oleic acid produced endogenously in the brain has been identified as an essential regulator of neurogenesis, learning, and memory in a study published in the Proceedings of the National Academy of Sciences. A Japanese cohort study found associations between oleic acid consumption and preservation of cognitive function in the elderly. A 2025 systematic review also found oleic acid among olive oil bioactive components that may contribute to neuroprotection.

Olive polyphenols (oleuropein, hydroxytyrosol, oleocanthal) have demonstrated neuroprotective activity against Alzheimer's-related amyloid-β and tau aggregation, neuroinflammation, and oxidative stress across preclinical and limited human studies. A study in mild cognitive impairment patients found 12 months of EVOO consumption modulated Alzheimer's-related blood biomarkers. The evidence is primarily mechanistic and epidemiological with emerging human data.

Multiple clinical studies support EVOO's neuroprotective role, including a small RCT showing improved clinical dementia ratings and blood-brain barrier function in mild cognitive impairment. PREDIMED sub-studies link Mediterranean diet with EVOO to better memory and frontal cognition. Epidemiological data associate higher olive oil intake with lower neurodegenerative disease risk.

Omega-3 fatty acids (primarily DHA and EPA) have been extensively studied in human clinical trials and observational research for their role in cognitive aging. Evidence is mixed: observational studies and some RCTs suggest benefit—particularly in individuals with mild cognitive impairment (MCI)—while trials in cognitively healthy older adults or those with established Alzheimer's disease generally show no significant effect. The overall body of evidence is real but inconsistent, with effect sizes that tend to be small and findings that are highly population- and dose-dependent.

Omega-6 PUFAs, particularly AA, are essential structural brain lipids whose adequate levels support neuronal membrane integrity across the lifespan. Observational cohort data show weak but statistically significant associations between plasma omega-6 levels and executive function, with high omega-6 levels associated with lower executive function in elderly cohorts. The omega-6:omega-3 balance rather than omega-6 alone appears to be the key determinant of cognitive outcomes.

Oleic acid (omega-9) is a major constituent of brain membrane phospholipids and myelin, and is essential for normal brain development and function. Lower OA levels have been found in brains of Alzheimer's disease patients. Rodent studies show OA neuroprotection via PPAR-γ activation, and Mediterranean dietary patterns rich in OA are associated with lower dementia risk.

A 2020 American Journal of Clinical Nutrition study found that a flavonoid-rich diet (of which onion is a primary source) reduces risk of Alzheimer's disease and related dementias. Quercetin from onion demonstrates neuroprotective effects in animal models, improving memory and sensorimotor function by reducing cerebral infarct size and oxidative stress.

Ophiopogon japonicus and its compounds have demonstrated neuroprotective effects in preclinical studies, including protection against neurodegeneration-related pathways. Multiple pharmacological reviews identify neuroprotective activity as a documented pharmacological property of the plant.

Hesperidin, the primary orange flavanone, has documented neuroprotective properties supported by clinical evidence showing improvements in cerebral blood flow, cognition, and memory. A 2025 Frontiers in Nutrition review characterised hesperidin as a neuroprotective candidate for age-related cognitive decline via antioxidant, anti-inflammatory, and neuro-regulatory mechanisms.

Oyster mushrooms are a leading source of ergothioneine, whose low blood levels correlate with cognitive decline and dementia. An RCT found that 12-week oyster mushroom supplementation improved episodic memory and maintained mood versus placebo. An active 12-week blinded RCT (OYSCOG trial) is specifically investigating cognitive outcomes in older adults.

Palm oil-derived tocotrienols have demonstrated neuroprotective effects in animal Alzheimer's disease models and a landmark 2-year human RCT showed attenuation of brain white matter lesion progression. Growing clinical trial evidence supports palm TRF's potential to slow neurodegeneration and reduce cognitive decline risk. Systematic reviews characterize TRF as a promising supplement for cognitive health in aging.

A 16-week RCT found daily peanut consumption improved brain vascular function and verbal memory in older adults. Niacin from foods (peanuts are a primary source) was prospectively associated with slower cognitive decline in ~4,000 adults over 65. Peanut skin polyphenols show neuroprotective effects in preclinical models.

PREP activity changes during aging and is altered in neurodegenerative conditions including Alzheimer's disease and Parkinson's disease. Decreased PREP activity in cerebrospinal fluid has been documented in Parkinson's disease patients, and PREP colocalizes with α-synuclein, β-amyloid, and tau protein in post-mortem human brain tissue. PREP inhibitors have been explored as potential disease-modifying agents for neurodegenerative disease.

A 12-month human RCT found perilla seed oil supplementation (1.47 mL/day) improved cognitive index scores in Japanese seniors, associated with reduced triglycerides and oxidative stress. Animal models show Perilla protects against vascular dementia-associated neuronal damage and amyloid-beta-induced cognitive impairment via anti-inflammatory and antioxidant mechanisms.

Phosphatidylcholine (PC) is a major structural component of neuronal cell membranes and a key choline source for acetylcholine synthesis—a neurotransmitter critically depleted in Alzheimer's disease. Observational studies link higher dietary PC intake to lower dementia risk, and elevated plasma PC species are associated with slower cognitive decline longitudinally. However, RCTs of PC supplementation in cognitively impaired populations have not demonstrated clear cognitive benefit, making the evidence strongest for dietary adequacy and biomarker associations rather than supplementation per se.

Phosphatidylserine (PS) is a phospholipid concentrated in neuronal cell membranes that has been evaluated in multiple randomized, placebo-controlled trials for age-related cognitive decline. Clinical studies—primarily using 300 mg/day—have shown statistically significant improvements in memory and cognitive parameters in elderly populations with cognitive impairment. In 2003, the U.S. FDA granted PS a qualified health claim permitting statements that it 'may reduce the risk of dementia and cognitive dysfunction in the elderly,' though with a mandatory disclaimer that the supporting evidence is 'very limited and preliminary.' Evidence strength is mixed: older bovine cortex-derived PS trials showed more consistent effects, while results from modern plant-derived (soy) forms are smaller and less uniform.

Eight RDP clinical trials show Pycnogenol (pine bark extract) improves memory-based cognitive functions across all age groups. In elderly subjects, spatial working memory improved by 10.9% and quality of working memory by 8.5% versus placebo. A 2019 Frontiers in Pharmacology review confirmed neuroprotective and cognitive benefits.

Multiple RCTs and a PMC systematic review confirm Pycnogenol improves cognitive function in older adults, including spatial memory, learning, and daily capabilities. It has been tested specifically in elderly populations and individuals with mild cognitive dysfunction. Antioxidant neuroprotection and cerebrovascular improvements are key mechanisms.

P. tenuifolia and its active saponin constituents show multiplex neuroprotective effects relevant to age-related cognitive decline, including anti-amyloid, anti-Tau, antioxidant, anti-apoptotic, and cholinergic-enhancing mechanisms. A 2024 meta-analysis found that PT-containing formulas improved cognition in Alzheimer's patients. The evidence base is predominantly preclinical.

Polygala root exhibits multiplex neuroprotective potential relevant to cognitive aging, including anti-amyloid, anti-tau, antioxidant, and anti-apoptotic effects in Alzheimer's disease models. Human trials in elderly populations demonstrate memory improvement. It is used in Korean functional foods for cognitive function and is a subject of Alzheimer's drug research.

A human pilot RCT (28 older adults) found pomegranate juice improved verbal and visual memory and brain activation on fMRI. Animal models show pomegranate attenuates Alzheimer's-related cognitive decline. A 2022 Frontiers in Aging Neuroscience review summarizes pomegranate's neuroprotective potential for age-related neurological disorders. Evidence is promising but limited to small trials.

Naringin from pomelo prevents cognitive dysfunction in D-galactose-induced aging rat models via TLR4/NF-κB pathway inhibition and restoration of BDNF/NGF neurotrophic factors. Naringenin (pomelo's primary aglycone) activates Nrf2, SIRT1, and PI3K/Akt neuroprotective pathways documented to counteract brain aging hallmarks. A 2025 PMC review concluded these mechanisms target age-related synaptic and mitochondrial deterioration.

Pregnenolone levels decline 1–2% per year after age 30, reaching 30–50% of peak values by age 70. This decline reduces substrate for all downstream steroids and is associated with cognitive aging. Neuroprotective and neuroplasticity-promoting effects of pregnenolone are well-documented preclinically, with supportive human clinical data.

PQQ disodium salt has been studied in older adults with and without mild cognitive impairment. A 2024 RCT in elderly individuals with MCI (mean age ~72 years) found a dihydrogen-PQQ combination improved mental orientation and brain metabolism. Earlier RCTs in healthy older adults (40–80 years) documented cognitive improvements at 20 mg/day over 12 weeks.

Quercetin, a flavonoid found widely in fruits and vegetables, has demonstrated neuroprotective effects through multiple mechanisms including antioxidant activity, anti-neuroinflammation, and inhibition of amyloid-beta aggregation — primarily in preclinical (cell and animal) studies. A 40-week randomized, double-blind, placebo-controlled human trial found that 110 mg/day of quercetin glycosides improved reaction time and preserved cerebral blood flow in older adults with age-related memory decline. However, at least one separate human RCT (12 weeks, queried general community sample) found no significant cognitive benefit, and the overall human evidence base remains limited, with several ongoing early-phase clinical trials.

Catalpol and Rehmannia oligosaccharides demonstrate neuroprotective activity against Alzheimer's disease models in animals and C. elegans. Catalpol reduces amyloid-beta toxicity, oxidative stress, and neuronal apoptosis, and a systematic review confirmed neuroprotective activity against AD, Parkinson's, stroke, and depression. Rehmannia is also used in classical TCM formulas for dementia and cognitive decline.

Catalpol and related compounds from R. glutinosa protect against neurodegenerative processes relevant to cognitive aging. Multiple preclinical studies show improvements in spatial memory, synaptic plasticity, and reduction of Alzheimer's-related pathology. TCM has used rehmannia for age-related dementia and memory loss for centuries.

Reishi exerts neuroprotective effects via antioxidant, anti-neuroinflammatory, and BDNF-upregulating mechanisms relevant to aging-related cognitive decline. A small RCT showed improved cognitive function in breast cancer patients on endocrine therapy. MSKCC notes a pilot study in Alzheimer's disease did not demonstrate benefit. Traditional use as a longevity and mental clarity tonic is extensive.

Resveratrol, a polyphenol found in grapes and red wine, has been investigated in multiple human randomized controlled trials for its potential to slow cognitive decline and support healthy aging. Clinical evidence shows it can improve cerebral blood flow, modulate Alzheimer's disease biomarkers (particularly CSF Aβ40), and in some trials improve memory and activities of daily living. However, results across trials are mixed, with several studies showing no significant improvement in standard cognitive scores (e.g., MMSE), and one large trial noting an unexpected increase in brain volume loss. Overall, the human evidence is promising but inconsistent, and larger, well-powered trials are needed.

Rhodiola rosea demonstrates antioxidant, anti-inflammatory, anti-apoptotic, and neuroprotective properties relevant to cognitive aging, supported by substantial preclinical evidence and some human clinical data on cognitive function and stress-related mental fatigue. Its key bioactive compounds—salidroside and rosavins—modulate oxidative stress and neuroinflammatory pathways implicated in age-related neurodegeneration. However, no clinical trials have directly tested Rhodiola for prevention of age-related cognitive decline or dementia, leaving the human evidence strongest for stress-induced cognitive impairment rather than neurodegeneration per se.

Epidemiological studies consistently associate coffee consumption with reduced risk of dementia and Alzheimer's disease. Robusta coffee's caffeine and chlorogenic acids modulate multiple pathways involved in cognitive aging, including beta-amyloid accumulation, neuroinflammation, and oxidative stress. A published review specifically examined robusta coffee and neurodegenerative conditions including Alzheimer's disease, synthesising preclinical and epidemiological evidence.

Rosemary and its bioactives rosmarinic acid and carnosic acid have demonstrated neuroprotective effects in preclinical models of Alzheimer's and Parkinson's disease. Human studies show rosemary water and aromatherapy improve cognitive function markers in elderly adults. Carnosic acid crosses the blood-brain barrier and activates NRF2/Nrf2 pathways that protect against neurodegeneration.

RA-standardized Melissa officinalis extracts have shown cognitive-stabilizing effects in patients with mild-to-moderate Alzheimer's disease in multiple RCTs. RA inhibits amyloid-beta fibril formation, protects against neuroinflammation, and supports BDNF-dependent neuroplasticity. A 2025 narrative review concluded lemon balm (RA-standardized) can stabilize cognitive function in mild cognitive impairment and early AD.

Preclinical studies consistently show RJ reduces age-related cognitive decline, amyloid burden, and neurodegeneration in rodent aging and Alzheimer's models. One human combination-product RCT improved MCI cognitive scores. RJ's BDNF-promoting, anti-inflammatory, and neurogenic properties support anti-aging neurological use.

Rutin has been studied in Alzheimer's, vascular dementia, and aging-related cognitive models with consistent preclinical benefit via antioxidant, anti-inflammatory, and anti-amyloid mechanisms. It addresses oxidative stress and neuroinflammation — core mechanisms of age-related cognitive decline.

Saffron (Crocus sativus L.) has been evaluated in multiple randomized, double-blind clinical trials for cognitive decline, mild cognitive impairment (MCI), and Alzheimer's disease (AD). A 2020 systematic review and meta-analysis of RCTs found saffron significantly improved cognitive scores (ADAS-cog, CDR-SB) versus placebo, with performance statistically comparable to standard drugs donepezil and memantine. Evidence is promising but currently limited by small sample sizes and a restricted geographic pool of trials, and no clinical recommendations can yet be made.

Sage demonstrates clinical efficacy in slowing cognitive decline in Alzheimer's patients and in preclinical and human studies of aging-related neurodegeneration. Multiple mechanisms converge, including AChE inhibition, antineuroinflammatory, and antioxidant effects. A 4-month RCT in Alzheimer's patients showed significant improvement on standardized cognitive scales.

SAMe is the brain's principal methyl donor, supporting DNA methylation, neurotransmitter synthesis, and phospholipid metabolism—all processes that decline with age. Post-mortem studies show severely depleted SAMe levels in Alzheimer's disease (AD) brain tissue, and transmethylation pathway dysregulation is broadly implicated in AD pathology. One small clinical trial in elderly patients with organic brain syndrome reported significant improvements in MMSE and geriatric assessment scores after 60 days of SAMe treatment (p<0.01). However, no large randomized controlled trials specifically targeting cognitive decline prevention or dementia have been completed in humans, and a Phase II RCT is currently underway.

The Chiu et al. (2014) proof-of-concept RCT in healthy older adults specifically framed sceletium's PDE4-inhibiting cognitive benefits in the context of Alzheimer's disease risk. Network pharmacology analysis identified overlapping targets with neurodegenerative pathways. Early clinical results are promising but trial scale is small.

Schisandra lignans have shown neuroprotective effects in Alzheimer's disease models, including reduced amyloid plaque, decreased beta-secretase activity, and improved cognitive function in rodent models. A clinical study found that a schisandra-containing formulation reduced amyloid plaque in Alzheimer's patients. Animal polysaccharide studies show improved learning, memory, and restoration of gut-brain axis disruptions in AD models.

Schisandrins protect against multiple hallmarks of neurocognitive aging including amyloid-β accumulation, neuroinflammation, oxidative stress, ER stress, and mitochondrial dysfunction. Multiple preclinical models of Alzheimer's disease show benefit, and the antiaging biological activity of schisandrins is recognized in comprehensive pharmaceutical reviews.

SDG protects the blood-brain barrier (BBB) and reduces neuroinflammation in animal models of systemic inflammation and aseptic encephalitis. It inhibits leukocyte adhesion and migration across the BBB and dampens brain endothelial inflammatory responses. These neuroprotective and anti-neuroinflammatory effects are relevant to age-related cognitive decline driven by chronic neuroinflammation.

Observational studies link lower selenium status with cognitive decline and dementia risk, including Alzheimer's disease, supported by the brain's priority maintenance of selenium even during systemic deficiency. A systematic review and meta-analysis of 11 studies found some improvement in cognitive tests in MCI patients receiving selenium supplementation. However, the large PREADViSE RCT found no significant benefit of selenium supplementation for dementia prevention. Evidence remains inconsistent, with selenium status appearing relevant but supplementation not clearly beneficial in adequately nourished populations.

Multiple preclinical studies demonstrate that selenomethionine mitigates cognitive decline in Alzheimer's disease and aging animal models by reducing tau hyperphosphorylation, enhancing autophagic clearance of tau, reducing amyloid plaque burden, and improving hippocampal cholinergic function. Brain selenium levels decline with age and correlate with cognitive performance. Human clinical trial data remain limited, making this a well-mechanized but partially preclinical evidence base.

Sesamin protects neurons from oxidative injury via multiple mechanisms: scavenging H₂O₂-driven ROS, reversing BCL-2 decline, limiting caspase-mediated apoptosis in neuroblastoma cells, preserving mitochondrial Sirtuin 3, and reducing JNK-mediated neuroinflammation. Sesame's omega-6 fatty acids support neural membrane integrity. Evidence is primarily preclinical/mechanistic; limited human clinical data specifically for cognitive outcomes.

Silicon may reduce cognitive decline risk via its antagonism of aluminum neurotoxicity: OSA reduces gastrointestinal aluminum absorption and increases urinary aluminum excretion. A pilot clinical study in Alzheimer's patients found that 12 weeks of silicon-rich mineral water reduced body aluminum burden and produced clinically relevant cognitive improvements in a subset of participants. Evidence remains preliminary.

Silymarin has documented neuroprotective effects in Alzheimer's disease and cognitive impairment models, reducing amyloid-beta deposition and neuroinflammation. Multiple review papers in peer-reviewed journals have catalogued its evidence base for cognitive protection. Evidence is predominantly preclinical (animal and cell models); controlled human trials for cognitive outcomes are very limited.

S. japonica is linked to cognitive benefits and longevity in traditional Korean and Chinese medicine texts. A registered randomized double-blind placebo-controlled trial (100 participants aged 40–70) is currently evaluating S. japonica extract for subjective memory complaints. Quercetin and rutin from the plant demonstrate neuroprotective properties in preclinical models.

Epidemiological studies in East Asia associate high soy isoflavone intake with lower risk of cognitive decline and dementia. The gut microbial metabolite S-equol is inversely associated with arterial stiffness and white matter lesions—key vascular contributors to cognitive impairment. RCTs in Western populations show inconsistent cognitive effects, partly attributed to lower equol-producer rates.

Clinical evidence from multiple RCTs and a meta-analysis of 16 trials suggests soy isoflavones can modestly slow or attenuate cognitive decline in older adults, with benefits in memory and overall cognitive function. Evidence is heterogeneous and equol-producer status may be a key moderator.

Soy isoflavones are investigated for potential protection against age-related cognitive decline and dementia via estrogenic and antioxidant mechanisms in the brain. Epidemiological studies in East Asian populations with high soy consumption show inverse associations between isoflavone intake and cognitive decline. RCTs in Western populations have not consistently replicated cognitive benefits, with the discrepancy attributed to gut microbiota-dependent equol production differences between populations.

Higher green leafy vegetable consumption, explicitly including spinach, is associated with significantly slower cognitive decline in a large prospective cohort study (n=960, ~5-year follow-up, Rush Memory and Aging Project). Participants consuming ~1.3 servings/day showed cognitive function equivalent to being 11 years younger than those consuming little or no greens.

A 2021 scoping review (PMC) of experimental and clinical evidence found preliminary clinical studies suggest spirulina can reduce mental fatigue, protect brain vessel endothelium from damage, and regulate internal pressure, potentially contributing to cerebrovascular health. Use of spirulina in malnourished children has been shown to ameliorate motor, language, and cognitive skills. Robust human RCT data specifically targeting cognitive decline in aging adults are limited; preclinical and mechanistic evidence is more extensive.

SPM levels are reduced in postmortem Alzheimer's disease brain tissue (hippocampus, entorhinal cortex) and in CSF of AD patients. Maresin 1 improved cognitive performance in AD mouse models. SPM receptor expression is altered in human AD brain, and SPM deficiency contributes to persistent neuroinflammation.

Stigmasterol protects neuronal cells from oxidative stress-induced death, attenuates Alzheimer's pathology in transgenic mice, and improves cognitive performance in neurotoxin-induced impairment models. Proposed mechanisms include AChE inhibition, antioxidant enzyme activation, and neuroinflammation suppression.

Strawberry intake is associated with reduced Alzheimer's dementia risk and less neuropathology (amyloid-β and tau tangles) in large cohort and autopsy-based studies at Rush University. A double-blind RCT found daily freeze-dried strawberry powder improved cognitive processing speed in older adults. The anthocyanidin pelargonidin, found predominantly in strawberries, is identified as the key bioactive.

Sulforaphane shows neuroprotective effects against age-related cognitive decline by increasing brain glutathione, reducing neuroinflammation, supporting BDNF-driven neuroplasticity, and protecting against amyloid-β and tau pathology. Human RCTs in older adults and schizophrenia demonstrate cognitive benefits.

A. calamus extracts show AChE inhibitory activity relevant to Alzheimer's pathology, neuroprotective effects in ischemia models, and antioxidant activity that may combat age-related neurodegeneration. Traditional use as a brain rejuvenator (medhya rasayana) spans millennia. No human RCTs targeting cognitive decline have been completed.

CX rhizome extract mitigated vascular dementia-like cognitive impairment in mice with bilateral carotid artery stenosis via inhibition of astrocyte and microglia activation. CX extract reduced β-amyloid aggregation and extended lifespan in C. elegans models. TMP and ligustilide have been shown to improve learning and memory in animal models of aging and ischemia.

Lower circulating taurine correlates with higher dementia risk in observational data. Taurine supports hippocampal neurogenesis, inhibits amyloid-beta-related toxicity in animal models, and improves cognitive measures in animal aging studies. A 2024 systematic review found compelling preclinical evidence for taurine's role in Alzheimer's disease, though human RCT data for cognitive outcomes are limited.

T. chebula is used in Ayurveda as a Rasayana for brain health and longevity. A proof-of-concept RCT demonstrated cognitive improvements in aging adults with memory complaints. Preclinical evidence supports neuroprotective mechanisms including BDNF upregulation, antioxidant protection of neural tissue, and anti-neuroinflammatory effects.

MgT (with threonic acid as active ligand) has been tested specifically for age-related cognitive decline in multiple RCTs. The key 2016 RCT in older adults with mild cognitive impairment showed a ~9-year cognitive age reversal. A 2026 RCT showed a 7.5-year reduction in brain cognitive age. An open-label trial in Alzheimer's patients showed improved regional cerebral metabolism.

Elevated homocysteine is consistently associated with cognitive impairment and Alzheimer's disease risk, and TMG reliably lowers homocysteine. A 24-week DB-RCT in 195 older adults found plasma betaine positively associated with construction, sensorimotor speed, and executive function at baseline; participants with the largest betaine increases showed borderline-significant memory improvement. Animal models demonstrate betaine attenuates homocysteine-induced cognitive impairment via NLRP3 inflammasome suppression.

A 2-year RCT demonstrated tocotrienol supplementation significantly attenuated progression of brain white matter lesions compared to placebo in humans—the first supplement to demonstrate structural neuroprotection in a blinded human trial. Epidemiological studies also associate higher plasma tocotrienol levels with better cognitive outcomes and reduced Alzheimer's disease risk.

Trans-pterostilbene (PTE), a dimethylated stilbene found naturally in blueberries and grapes, has substantial preclinical evidence supporting neuroprotective and anti-aging effects relevant to cognitive decline. It crosses the blood-brain barrier, modulates oxidative stress, neuroinflammation, synaptic plasticity, and sirtuin/SIRT1 pathways. However, as of late 2023–2024, no clinical trials have confirmed cognitive benefits specifically in humans with age-related cognitive decline or dementia, making the evidence base preclinical rather than clinically validated for this indication. One small human RCT (n=32) in ALS patients tested a PTE+nicotinamide riboside combination with positive functional outcomes, but this does not directly address cognitive aging.

Multiple clinical trials and systematic reviews demonstrate curcumin improves cognitive function in older adults, particularly working memory and cognitive speed. A meta-analysis of 6 RCTs (289 subjects) found significant cognitive improvement in older adults (SMD=0.33, p=0.02). Mechanisms include anti-neuroinflammatory, BDNF-upregulating, and amyloid-modulating properties relevant to Alzheimer's disease risk.

CoQ10/ubiquinol has been investigated for cognitive decline given its roles in mitochondrial energy production, antioxidant defense, and vascular function—all implicated in age-related cognitive impairment. A 90-day RCT specifically testing 200 mg/day ubiquinol for cognitive outcomes in healthy elderly adults (≥60 years) has been registered and conducted. A 2025 PMC review confirms CoQ10 as a promising intervention for cognitive aging.

Uridine is a pyrimidine nucleoside that serves as a key precursor for membrane phospholipid (phosphatidylcholine) synthesis, directly supporting synapse formation and neuronal membrane integrity. Blood levels of uridine are measurably lower in patients with Alzheimer's disease and mild cognitive impairment (MCI), framing it as a conditionally essential nutrient in these populations. The strongest clinical evidence comes not from uridine alone, but from its use as a core component of the multinutrient formula Souvenaid (containing uridine monophosphate, choline, and DHA), which in the LipiDiDiet RCT in prodromal AD showed stabilization of cognition, slowing of hippocampal atrophy, and significant benefits on disease progression at 36 months. Single-agent uridine supplementation trials in humans remain sparse and have not independently demonstrated robust cognitive benefits.

UA is increasingly studied for cognitive aging due to its BBB permeability, mitophagy-activating mechanism in neurons, and anti-neuroinflammatory effects. Preclinical studies show benefits in Alzheimer's and aging-related cognitive models. Human data from adjacent trials show systemic healthy-aging biomarker improvements; dedicated cognitive aging RCTs are underway.

Vinpocetine is a synthetic derivative of the Vinca minor alkaloid vincamine, studied clinically for cognitive impairment and age-related cerebrovascular decline. Its primary mechanism involves inhibition of phosphodiesterase type 1 (PDE1), which elevates cAMP/cGMP, improves cerebral blood flow, and supports neuronal plasticity. A Cochrane review of three randomized controlled trials (583 patients) found signals of benefit at 30–60 mg/day but concluded the evidence is inconclusive due to small sample sizes, short duration, and inconsistent adverse-effect reporting. Vinpocetine has not been approved by any regulatory body for treating cognitive impairment.

Thiamine-dependent enzyme activity is reduced in Alzheimer's disease brains, and thiamine deficiency in animal models recapitulates core AD pathology including tau hyperphosphorylation and amyloid deposition. A 12-month benfotiamine RCT in mild AD slowed cognitive decline significantly. A cross-sectional study found a J-shaped association between dietary thiamine intake and cognitive performance in older adults.

Vitamin B12 has substantial clinical and observational evidence linking its status to cognitive decline in aging adults, primarily through the homocysteine-lowering and myelin-maintenance mechanisms. Low or suboptimal B12 levels are associated with accelerated cognitive decline, brain atrophy, and increased dementia risk. Intervention benefits appear most pronounced in individuals with pre-existing deficiency or elevated homocysteine, and in those with mild cognitive impairment rather than established dementia. Evidence from supplementation trials is mixed overall, but long-duration RCTs (>12 months) show statistically significant slowing of decline.

Dietary niacin intake has been associated with reduced risk of Alzheimer's disease and cognitive decline in observational studies (Journal of Neurology, Neurosurgery & Psychiatry). NAD+ levels decline with age, and niacin/nicotinamide precursors are being investigated in clinical trials for Alzheimer's disease and age-related cognitive impairment. Preclinical models showed cognitive protection; human RCTs remain preliminary.

Multiple prospective observational studies link low vitamin B6 status (measured as plasma pyridoxal-5-phosphate, PLP) with significantly accelerated cognitive decline in older adults. The primary proposed mechanisms are homocysteine regulation and neurotransmitter biosynthesis. However, randomized controlled trials of B6 supplementation—often in combination with B12 and folate—have yielded inconsistent results, and a systematic review of 14 RCTs found insufficient evidence of benefit on cognitive function from supplementation alone.

Substantial epidemiological and clinical evidence links folate (vitamin B9) status to cognitive aging outcomes. Low serum folate and elevated homocysteine are consistently associated with greater cognitive decline and increased Alzheimer's disease risk. Intervention trials show benefit primarily in older adults with mild cognitive impairment and elevated homocysteine at baseline, though results in generally healthy or folate-replete populations are mixed.

There is a substantial body of human and clinical evidence linking vitamin C status to cognitive health in aging. Observational studies consistently show higher plasma vitamin C concentrations in cognitively intact older adults compared to cognitively impaired groups. However, intervention trials using vitamin C supplementation alone have not yet demonstrated conclusive benefits, and evidence remains equivocal. Correcting deficiency appears more important than high-dose supplementation.

Substantial observational and epidemiological evidence links low vitamin D3 status to increased risk of cognitive decline and dementia in older adults, supported by plausible neurobiological mechanisms. However, randomized controlled trials have produced largely null or mixed results, meaning supplementation has not been conclusively proven to prevent or slow cognitive decline in vitamin D-sufficient populations. The overall picture is one of an active, contested scientific relationship with promising signals but insufficient interventional proof.

Vitamin E, primarily as alpha-tocopherol, has been extensively studied in relation to cognitive decline and healthy aging due to its role as the brain's principal lipid-soluble antioxidant. Epidemiological studies and some prospective cohorts associate higher dietary vitamin E intake with reduced risk of dementia and slower cognitive decline. However, four Cochrane systematic reviews have consistently found insufficient evidence that alpha-tocopherol supplementation prevents progression from mild cognitive impairment (MCI) to Alzheimer's disease (AD) or meaningfully improves cognition in AD patients. The overall evidence base is mixed: dietary intake shows more promise than isolated high-dose supplementation.

A double-blind RCT in healthy adults 60+ showed 12 weeks of 6-MSITC supplementation significantly improved episodic memory. Preclinical research shows 6-MSITC protects dopaminergic neurons and reduces neuroinflammation, offering relevance to Alzheimer's and Parkinson's prevention. Nrf2 pathway activation in neurons underpins the neuroprotective mechanism.

Multiple RCTs in older adults show Bacopa monnieri slows age-related cognitive decline and enhances cognitive performance. The Calabrese et al. trial provided evidence that Bacopa safely enhances cognitive performance in aging. Preclinical mechanisms include β-amyloid reduction and neuroprotection, though human data for Alzheimer's disease specifically remain inconclusive.

Wheat germ-derived spermidine has been investigated in human RCTs for cognitive protection in older adults with subjective cognitive decline. The SmartAge trial (n=100, 12 months) used a spermidine-rich wheat germ extract but did not show significant improvement on the primary memory outcome. A prior phase II pilot confirmed safety. Mechanistic evidence in animal models supports spermidine's neuroprotective effects via autophagy.

A 2025 pilot human study found an association between habitual yerba mate consumption and reduced risk of cognitive impairment in adults over 50. Preclinical evidence shows YM reduces acetylcholinesterase activity and amyloid-beta expression. The neuroprotective evidence base remains at an early stage.

Multiple RCTs and meta-analyses support a link between lutein/zeaxanthin supplementation and slowed cognitive decline in older adults. An fMRI-based RCT (n=44, mean age 72) found that 12 mg/day L+Z for one year buffered verbal learning decline (Cohen's d=0.84) and enhanced cerebral perfusion in prefrontal regions. Epidemiological data consistently associate higher circulating zeaxanthin with better cognitive function and lower dementia incidence.

There is human and clinical evidence linking zinc status to cognitive health in aging. Zinc deficiency has been associated with increased dementia risk and poorer cognitive performance in observational and cohort studies, while a randomized controlled trial in older adults found modest benefits on spatial working memory with supplementation. The relationship is bidirectional and complex—both deficiency and dysregulated excess can impair brain function—and current evidence does not yet support supplementation as a treatment for established cognitive decline.

Amla is traditionally classified as a rejuvenating 'rasayana' herb in Ayurveda, used across millennia to slow cognitive aging. Mechanistic research supports neuroprotective and antioxidant effects, but dedicated human RCTs on cognitive decline are absent.

Paeoniflorin exerts neuroprotective effects in multiple animal models of cognitive impairment, including Alzheimer's-like models, via inhibition of amyloidogenesis, reduction of neuroinflammation, and upregulation of BDNF. Human clinical evidence for cognitive outcomes is absent.

Multiple preclinical studies show baicalin and baicalein protect hippocampal neurons, reduce neuroinflammation, and improve cognitive performance in animal models of Alzheimer's, Parkinson's, and cerebral hypoperfusion. EBSCO and Drugs.com note skullcap is investigated for Alzheimer's and Parkinson's neuroprotection, but clinical trials in humans are lacking.

Triphala is classified as a Rasayana (rejuvenative) in Ayurveda with traditional use for cognitive preservation and neuroprotection. Preclinical evidence supports antioxidant protection of neuronal tissue and prevention of immunosenescence. Dedicated human RCTs for cognitive outcomes are absent.