Sleep Quality: A Nutrition and Natural-Health Reference
1. Definition and Conceptual Framework
Sleep quality is defined as an individual's self-satisfaction with all aspects of the sleep experience, and it encompasses four core attributes: sleep efficiency, sleep latency, sleep duration, and wake after sleep onset. The concept is multidimensional, and its measurement has been standardised through validated instruments. Sleep quality is most widely assessed using the Pittsburgh Sleep Quality Index (PSQI), which encompasses seven components of self-reported sleep quality, sleep latency, sleep duration, habitual sleep efficiency, sleep disturbances, use of sleeping medication, and daytime dysfunction.
Although sleep quality has been measured using different strategies, from physiological responses to a single-item self-report question, there is some consensus that it encompasses several complementary aspects such as sleep duration, latency, efficiency, degree of fragmentation, total wake time, sleep disruptive events and daytime dysfunction, among others.
Sleep quality has both a subjective and an objective dimension. The "quality of sleep" may be evaluated from an objective and a subjective point of view. Objective sleep quality refers to how difficult it is for a person to fall asleep and remain in a sleeping state, and how many times they wake up during a single night. Subjective sleep quality refers to a sense of being rested and regenerated after awaking from sleep. A preliminary definition of sleep quality should include reference to tiredness on waking and throughout the day, feeling rested and restored on waking, and the number of awakenings in the night.
2. Body Systems Involved
2.1 The Nervous System and Sleep Architecture
Healthy sleep is a fundamental pillar of various neurophysiological, emotional, and cognitive processes, including emotion regulation, memory consolidation, and brain waste clearance. Physiological sleep consists of two main phases—the REM (rapid eye movements) phase and the NREM (non-REM) phase—which are repeated during sleep. The REM phase is associated with the activation of the sympathetic nervous system, and it leads to an increase in temperature and blood pressure and to an accelerated heart rate. During the REM sleep phase, there is also a decrease in muscle tone and activation in the limbic regions, which suggests that REM plays a role in emotional regulation.
The most restful sleep occurs during stages 3 and 4 NREM sleep, and one indicator of sleep quality is the percentage of time a patient spends in these sleep stages. Neurotransmitters involved in promoting wakefulness include acetylcholine, dopamine, glutamate, histamine, norepinephrine, orexin, and serotonin. The inhibitory neurotransmitter GABA plays a contrasting, sleep-promoting role: GABA, the principal inhibitory neurotransmitter in the central nervous system, not only suppresses neuronal excitability to promote sleep but also interacts with circadian clock genes to modulate sleep–wake rhythms.
Adenosine is an endogenous sleep-producing substance. A breakdown product of adenosine triphosphate (ATP), adenosine is believed to be a homeostatic sleep factor that mediates the transition from prolonged wakefulness to NREM sleep. Adenosine mediates this transition by inhibiting arousal-promoting neurons of the basal forebrain.
2.2 The Circadian System
The regulation of sleep is processed by the homeostatic physiology of the circadian rhythm, the sleep/wake cycle. Circadian rhythm is the 24-hour internal clock in our brain that regulates cycles of alertness and sleepiness by responding to light changes in our environment. The regulation of sleep in humans is governed by processes influenced by hormonal and environmental factors, including a daily sleep-wake cycle influenced by a circadian rhythm tied to light-dark cycles controlled by a cluster of about 10,000 neurons located in the hypothalamus behind the eyes, called the suprachiasmatic nuclei (SCN).
Clock genes regulate neurotransmitter systems (e.g., melatonin, serotonin, GABA, dopamine), mitochondrial function, and neuroimmune crosstalk, offering a molecular framework to explain sleep fragmentation and impaired sleep quality. Sleep continuity or sleep consolidation is an important determinant of sleep quality. The circadian process has a strong impact on this characteristic of sleep, such that the duration of awakenings is much shorter during the biological night than during the biological day.
2.3 The Endocrine and Immune Systems
During sleep, most of the body's systems are in an anabolic state, helping to restore the immune, nervous, skeletal, and muscular systems; which are vital processes that maintain mood, memory, and cognitive function and play a large role in the function of the endocrine and immune systems. During sleep, there is a decrease in the release of cortisol, norepinephrine, and adrenaline. The concentration of hormones that affect cell growth, such as growth hormones, melatonin, and prolactin, increases. Prolactin and growth hormone influence the differentiation and formation of new T cells and stimulate the function of type 1 cytokines that control the antigenic response of lymphocytes.
Two effector systems are responsible for regulating the immune response—the sympathetic nervous system and the hypothalamic–pituitary–adrenal axis—which are both influenced by sleep. When you sleep too little, the immune system produces a reduced number of antibodies, which are involved in the body's defensive reactions.
Cortisol shows a clear circadian pattern, with the peak occurring just before waking in diurnal animals such as humans. Circadian rhythms and sleep are fundamental biological processes integral to human health, and their disruption is associated with detrimental physiological consequences, including cognitive, metabolic, cardiovascular, and immunological dysfunctions.
3. Contributing and Associated Factors
3.1 Physiological Factors
Antecedents to sleep quality include physiological factors such as age, circadian rhythm, body mass index, NREM, and REM; psychological factors such as stress, anxiety, and depression; and environmental factors such as room temperature, television/device use, and family/social commitments.
Disruption of circadian rhythms and sleep is associated with detrimental physiological consequences, including cognitive, metabolic, cardiovascular, and immunological dysfunctions. Poor sleep health is a growing public health concern given that both short and poor sleep are consistently linked with heightened risk for cardiometabolic diseases, including obesity, type 2 diabetes, and cardiovascular disease.
3.2 Psychological and Environmental Factors
Stress, anxiety, and depression are among the most documented psychological antecedents to poor sleep quality. Physiological conditions associated with sleep quality may be organised into conditions of the cardiovascular, respiratory, muscle, and nervous systems, and conditions relating to blood chemistry. Environmental conditions may be broadly defined to include the environmental surroundings affecting the patient, such as ambient light, temperature, humidity, air pollution, noise, and barometric pressure.
3.3 Genetic Factors
Given the moderate heritability of circadian and sleep traits, genetics offers an opportunity that complements insights from model organism studies to advance fundamental molecular understanding of human circadian and sleep physiology and linked chronic disease biology.
4. Nutrients Studied in Relation to Sleep Quality
4.1 Tryptophan
Tryptophan is an essential amino acid that serves as the dietary precursor to serotonin and, downstream, to melatonin. Tryptophan, specifically its ratio relative to large neutral amino acids (LNAA) in the blood, appears to be a potential mediator of diet's effect on sleep. Tryptophan is a precursor of the synthesis of the serotonin neurotransmitter and melatonin hormone, which are both integral to sleep-wake regulation. Researchers have proposed that diets that increase the Trp:LNAA ratio allow for greater synthesis of these sleep-promoting factors. When Trp levels are increased, the amino acid can surpass other LNAA for transport across the blood-brain barrier. Once across, Trp is converted to serotonin, which in turn regulates sleep-wake.
Tryptophan is necessary for serotonin synthesis, and tryptophan depletion leads to sleep disturbances through the serotonergic pathway. Significant decreases in total sleep time, longer sleep onset latency, and reduced sleep efficiency occur after tryptophan restriction. Tryptophan deficiency is also associated with increased wake periods. Hence, consumption of tryptophan-rich food items like cereals and high-protein diets containing tryptophan can assist in improving sleep outcomes.
Evidence strength: A meta-analysis of 28 RCTs found that tryptophan, vitamin D, omega-3, zinc, and antioxidants may enhance sleep quality by decreasing sleep latency and wake after sleep onset, increasing sleep efficiency, and extending total sleep time. Evidence is primarily mechanistic and observational; well-powered, dedicated tryptophan supplementation trials in sleep-disordered populations are limited.
4.2 Melatonin
Melatonin is both a hormone synthesized endogenously in the pineal gland and a compound found in small amounts in various foods. Melatonin is a physiological indoleamine involved in circadian rhythm regulation and is currently used for secondary sleep disorders supported by empirical evidence.
Scientific evidence: A systematic review and meta-analysis was conducted to review the effect of melatonin on sleep quality as assessed by the Pittsburgh Sleep Quality Index (PSQI) in adults with various diseases, summarizing evidence from randomized clinical trials. Of 2,642 papers screened, 23 RCTs met inclusion criteria. Results indicated that melatonin had a significant effect on sleep quality as assessed by the PSQI (WMD: −1.24; 95% CI −1.77 to −0.71; p = 0.000).
A meta-analysis including a total of 34 RCTs (21 in children/adolescents: N = 984; 13 in adults: N = 1,014) found evidence that melatonin significantly improved sleep onset latency and total sleep time, but not sleep awakenings, in children and adolescents with a variety of neurodevelopmental disorders, and sleep onset latency as well as total sleep time in adults with delayed sleep phase disorder.
Pooled data demonstrate that exogenous melatonin lowers sleep onset latency and increases total sleep time, whereas it has little if any effect on sleep efficiency. A large scoping review of systematic reviews found that despite heterogeneity in review methods and outcome definitions, the direction of evidence consistently favored melatonin over placebo. According to GRADE methodology, weak recommendations were made for preventing phase shifts from jet lag, for improving insomnia in both healthy volunteers and individuals with a history of insomnia, and for initiating sleep and/or improving sleep efficacy.
4.3 Magnesium
Magnesium is an essential mineral involved in hundreds of enzymatic reactions and is of particular interest in sleep research because of its role in GABA receptor function and regulation of the HPA axis.
Scientific evidence: A study using 500 mg of daily magnesium supplementation showed improvements in sleep efficiency, sleep duration, sleep onset latency, and early-morning awakening frequency compared to placebo. A recent systematic review, encompassing 7,582 participants from 9 published cross-sectional, cohort, and randomized controlled studies, identified an association between magnesium status and sleep quality. The findings demonstrated that in healthy adults, higher magnesium intake was correlated with various sleep quality parameters, including daytime sleepiness, drowsiness, snoring, and sleep duration. Randomized controlled trials recorded positive impacts of magnesium supplementation on PSQI scores, sleep efficiency, and sleep duration.
A recent well-powered RCT found that a randomized, double-blind, placebo-controlled trial enrolled 155 adults aged 18–65 years with self-reported poor sleep quality. Participants were assigned to either magnesium bisglycinate (250 mg elemental magnesium daily) or placebo. The magnesium bisglycinate group showed a significantly greater reduction in Insomnia Severity Index (ISI) scores compared to the placebo group from baseline to week 4 (−3.9 vs −2.3; p = 0.049).
A recent systematic review concluded that while observational studies suggest an association between magnesium status and sleep quality, interventional trials have yielded inconsistent results, highlighting the need for well-designed studies with larger sample sizes and longer durations. However, growing evidence supports the role of magnesium supplementation in improving sleep outcomes. Magnesium has been implicated to benefit sleep, although clinical evidence varied based on the magnesium source used. Magnesium L-threonate is a promising form due to its brain bioavailability and effects on cognition, memory, and mood. Evidence strength: Preliminary to moderate; results are promising but heterogeneous across form, dose, and population.
4.4 Vitamin D
Clinical implications suggest that vitamin D supplementation may be a valuable adjunctive approach to managing sleep disorders. A dose of 50,000 IU bi-weekly for eight weeks proved effective in one study, though individual variations and underlying health conditions should be considered. Given the prevalence of vitamin D deficiency in various populations, optimizing vitamin D status could be a simple and cost-effective strategy to improve sleep quality. Evidence strength: Limited; further well-controlled studies are required.
4.5 Omega-3 Fatty Acids
Total sleep time as measured by actigraphy was negatively associated with intake of total fat and saturated fat. From limited studies, it seems that the consumption of saturated fatty acids deteriorates sleeping wellness. Conversely, omega-3 polyunsaturated fatty acids (PUFAs) have been associated with improved sleep. A high intake of fish and vegetables has a positive effect on sleep, and fatty fish is rich in vitamin D and omega-3 fatty acids.
The current body of literature converges to suggest that omega-3 fatty acids subjectively and objectively improve several sleep-related parameters and outcomes in young, older, and clinical cohorts. Evidence strength: Modest, primarily from observational studies; clinical trial data are limited but directionally positive.
4.6 L-Theanine
L-theanine, an amino acid primarily found in green tea, has gained attention for its potential impact on sleep due to its calming properties. The proposed mechanism for L-theanine's influence on sleep lies in its ability to modulate neurotransmitters. L-theanine readily crosses the blood-brain barrier and is known to increase the production of GABA.
In study outcomes, administration of L-theanine resulted in substantial decreases in stress-related symptoms and notable enhancements in cognitive function compared to placebo. L-theanine seems to present promising sleep-promoting properties. Evidence strength: Preliminary; current human trial data are limited in number and scale.
4.7 Glycine
Glycine seems to present promising sleep-promoting properties. Glycine is a non-essential amino acid proposed to improve sleep quality through peripheral vasodilatory effects that facilitate core body temperature reduction, a physiological precondition for sleep onset. Evidence strength: Very preliminary; trial data are limited to small studies, and larger well-controlled trials are needed.
5. Herbs and Natural Ingredients: Traditional Use and Scientific Evidence
5.1 Valerian Root (Valeriana officinalis L.)
Traditional Use
Over centuries, valerian root has been utilized to alleviate insomnia, nervousness, and restlessness, and it remains one of the most widely used herbal sleep aids in modern phytotherapy. Historically recommended as a sedative since the second century, valerian has gained popularity as a natural remedy in both Europe and the United States. The root of the valerian plant is the part used for medicinal purposes, commonly consumed as dried herb, extract, or in tea form.
Proposed Mechanisms
Pharmacological studies suggest that valerian may exert its effects through multiple neuromodulatory pathways, including interactions with the adenosine, serotonin, and GABAergic systems. Valerian roots and rhizomes contain a complex mixture of bioactive compounds such as monoterpenes, sesquiterpenes, flavonoids, caffeic acids, and lignans. Collectively, these compounds contribute to the multifaceted pharmacological effects of valerian, supporting its traditional use in alleviating sleep disorders. Research suggests that valerian might influence GABA levels, akin to conventional tranquilizers, yet the exact mechanisms remain unclear.
Scientific Evidence
PubMed, ScienceDirect, and Cochrane Library were searched in a systematic review and meta-analysis. A total of 60 studies (n = 6,894) were included, and meta-analyses were performed to evaluate the effectiveness to improve subjective sleep quality (10 studies, n = 1,065) and to reduce anxiety (8 studies, n = 535). Valerian is a popular herbal medicine used as a sleep aid; however, the outcomes of previous clinical studies are inconsistent.
Evidence from clinical studies of the efficacy of valerian in treating sleep disorders such as insomnia is inconclusive. Constituents of valerian have been shown to have sedative effects in animals, but there is no scientific agreement on valerian's mechanisms of action. A systematic review concluded that, although valerian is a safe herb, evidence did not support the clinical efficacy of valerian as a sleep aid for insomnia. Popular herbal remedies with a long-standing history of traditional medicinal use, namely valerian root extracts, lack adequate support to justify their use in individuals experiencing sleep disorders.
Evidence strength: Overall weak and inconsistent in human trials; animal and in vitro studies suggest sedative activity but human RCT findings remain mixed. The NIH Office of Dietary Supplements characterises the clinical evidence as inconclusive.
5.2 Ashwagandha (Withania somnifera L.)
Traditional Use
Ashwagandha (Withania somnifera), an essential medicine in Ayurveda, is reportedly beneficial in reducing stress and improving memory. In classical Ayurvedic texts, the root was used as a rasayana (rejuvenating tonic) to improve energy, vitality, and sleep quality in the elderly, and was traditionally prepared as a milk decoction.
Scientific Evidence
A double-blind, randomized, placebo-controlled clinical study evaluated the effect of ashwagandha root extract (300 mg sustained-release capsule) on cognitive functions, stress levels, sleep quality, and overall well-being in 130 healthy, cognitively sound stressed adults aged 20–55 years, who took one capsule daily for 90 consecutive days. Treatment improved memory and focus, psychological well-being, and sleep quality, reduced stress levels, and was safe and well-tolerated.
In a study of elderly participants, statistically significant improvement was observed in the ashwagandha treatment group compared to placebo, and a significant increase in the quality of sleep (p < 0.0001) and mental alertness (p < 0.034) was observed compared to the placebo group.
Ashwagandha may be considered a subsidiary sleep aid by working in synergy with other soporific nutrients or by addressing concomitant physiological mechanisms that may disrupt healthy sleep–wake patterns by indirect routes. Evidence strength: Preliminary to moderate; studies are limited in number and mostly use proprietary extracts; beneficial effects appear linked to stress reduction rather than direct hypnotic activity.
5.3 Chamomile (Matricaria chamomilla) and Apigenin
Chamomile (Matricaria chamomilla and Chamaemelum nobile) has been used in European and Middle Eastern traditions for centuries as an infusion to relieve nervousness and promote sleep. The primary bioactive flavone is apigenin, which is proposed to act as a partial agonist at benzodiazepine receptors. The current body of literature converges to suggest that apigenin-containing chamomile subjectively and objectively improves several sleep-related parameters and outcomes in young, older, and clinical cohorts. Evidence strength: Preliminary to modest; small RCT data are positive but large-scale trials are lacking.
5.4 Tart Cherry (Prunus cerasus)
Tart cherry is not a traditional herbal medicine in the classical sense, but it has emerged as a food-based source of phytochemicals with sleep-relevant activity, including melatonin and anthocyanins.
Scientific evidence: A pilot study investigated the effects of tart cherry juice on sleep quality and insomnia severity in 15 older adults with chronic insomnia. The participants consumed tart cherry juice for 2 weeks. The study reported significant improvements in sleep quality, sleep latency, and insomnia severity in the tart cherry group compared to baseline. The authors suggested that the high melatonin content of tart cherries may be responsible for their sleep-promoting effects. In a 2025 systematic review of seven interventional studies, three reported significant improvements in sleep indicators such as sleep duration, sleep efficiency, or sleep onset time, and three also reported an increase in melatonin levels after tart cherry consumption. However, there were large differences in dose, duration of intervention, and characteristics of the participating populations. Although tart cherry consumption may be effective in improving sleep quality, reducing inflammation, and increasing antioxidant capacity, the available evidence is still limited and heterogeneous.
Evidence strength: Preliminary; supportive but small trials; high-quality large RCTs are needed to confirm efficacy and clarify dose-response.
5.5 Kiwifruit (Actinidia deliciosa)
Kiwifruit has received research interest because of its serotonin precursor content, antioxidant profile, and folate content. The current body of literature converges to suggest that kiwifruit subjectively and objectively improves several sleep-related parameters and outcomes in young, older, and clinical cohorts. Published human studies have been small; evidence is preliminary.
6. Dietary and Macronutrient Factors
6.1 Overall Diet Quality
Proper nutrition involves providing all of the necessary nutrients in order to maintain health and wellbeing. The foods that people consume can not only influence their wakefulness during the day, but also their quality of sleep. Sleep is not only influenced by the energy efficiency of the diet, but also by the content of macronutrients. Experimental data indicate that provision of specific foods rich in tryptophan or melatonin can improve sleep quality. Whole diets rich in fruits, vegetables, legumes, and other sources of dietary tryptophan and melatonin have been shown to predict favorable sleep outcomes.
Key focus areas in nutritional research include sleep-supportive nutrients, dietary patterns such as the Mediterranean, ketogenic, and plant-based diets, chrononutrition, and gut-brain axis modulation. Evidence supports the role of specific nutrients such as magnesium, tryptophan, and omega-3 fatty acids, as well as dietary patterns rich in anti-inflammatory and antioxidant compounds, in improving sleep outcomes.
6.2 Tryptophan-Rich Foods
Strategic dietary intake of tryptophan-rich foods such as milk, eggs, cheese, poultry, and fish will enhance serum tryptophan availability, thereby potentiating melatonin biosynthesis and subsequent sleep optimization. Milk is widely considered a sleep-promoting food in many cultures worldwide. Children are often given milk with turmeric before bedtime in certain Eastern cultures. Cow milk has high levels of tryptophan and is conducive to sleep.
6.3 Saturated Fat and Dietary Fat Composition
Total sleep time as measured by actigraphy was negatively associated with intake of total fat and saturated fat. From limited studies, consumption of saturated fatty acids appears to deteriorate sleeping wellness. This is also true if diabetes is induced due to the long-term consumption of saturated fatty acids, as diabetes is often associated with sleeping problems.
7. Stimulants and Other Dietary Factors
7.1 Caffeine
Caffeine has long been associated with sleep disorders. Evidence has grown indicating the stimulating effect of caffeine, and the extent to which regular users may merely be restoring normal functioning after abstinence from caffeine. Caffeine interrupts sleep, with sleep hygiene instructions calling for stopping caffeine consumption before bed. However, caffeine response at bedtime is variable, and withdrawal may confuse studies.
7.2 Alcohol
Alcohol misuse impairs sleep quality and circadian rhythms. Substances such as alcohol, nicotine, excess caffeine, and cannabis negatively affect the quality of sleep. They cause, among other things, an increase in the waking time after falling asleep. While alcohol is commonly believed to act as a sedative, research indicates it disrupts sleep architecture, particularly suppressing REM sleep in the second half of the night.
7.3 General Dietary Pattern Considerations
Proper nutrition that is rich in tryptophan, vitamin D, and gamma-aminobutyric acid can improve the quality of sleep. By using foods that are rich in these substances, the effectiveness and the actual sleep time are improved. Both the quantity and the quality of sleep can be largely improved with relatively straightforward practices dictated by good sleep hygiene; emerging research suggests that dietary and supplementation protocols focused on certain foods, nutrients, and biochemical compounds with sleep-promoting properties can act as subsidiary sleep aids in complementing these behavioral changes.
8. Physical Activity and Lifestyle Factors
Regular physical activity has several health benefits, including improved sleep quality and symptoms of sleep disorders. Moderate-intensity exercise can improve sleep quality in insomnia patients. Patients with insomnia who exercised for 30 minutes three times per week for eight weeks experienced improved sleep quality. Additionally, moderate-intensity aerobic exercise improves sleep among patients with insomnia.
A systematic review revealed that evening exercise may positively affect sleep, but vigorous exercise might impair sleep-onset latency and total sleep time. The relationship between physical activity intensity and sleep quality is therefore nuanced and warrants context-specific consideration.
Sleep reduces energy consumption, as the basic metabolic rate decreases, partly because it reduces body temperature. Light exposure, consistent sleep-wake schedules, management of psychological stress, and minimization of artificial light at night are also recognised as important lifestyle modulators of sleep quality in the literature, operating primarily through the circadian system.
9. Evidence Summary
- Melatonin: Most consistent evidence base among natural sleep-related compounds; multiple meta-analyses of RCTs support reductions in sleep onset latency and improvements in total sleep time, particularly for circadian disruption and secondary sleep disorders. GRADE-rated evidence is characterised as weak to moderate.
- Magnesium: Growing evidence from observational studies and RCTs supporting associations with sleep quality; clinical trial data are promising but heterogeneous. Evidence is characterised as preliminary to moderate.
- Tryptophan/dietary precursors: Mechanistic and epidemiological evidence is strong; dedicated supplementation trial evidence is more limited but directionally positive.
- Omega-3 fatty acids: Observational and some interventional evidence is supportive; clinical trial data are still limited.
- Valerian root: Long traditional history; multiple systematic reviews conclude clinical evidence is inconclusive and inconsistent. The NIH ODS characterises the evidence as inconclusive.
- Ashwagandha: Preliminary positive RCT data, primarily through stress and cortisol pathways; further independent replication is needed.
- Tart cherry, kiwifruit, chamomile/apigenin: Early-stage evidence is supportive but limited in scope and scale; larger trials are required.
- L-theanine, glycine: Promising mechanistic rationale and preliminary human data; evidence base is nascent.
- Caffeine and alcohol: Consistent evidence of detrimental effects on sleep architecture; widely replicated across multiple study designs.
- Physical activity: Moderate-intensity exercise has a well-supported, positive association with sleep quality across multiple systematic reviews.
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