L-Serine: A Comprehensive Encyclopedic Reference
1. Identity, Chemistry, and Natural Sources
Chemical Identity
L-serine (C₃H₇NO₃; 105.09 g/mol) is a naturally-occurring dietary amino acid, with the systematic synonym (S)-2-amino-3-hydroxypropanoic acid. Also known as 2-amino-3-hydroxypropanoic acid, it is a neutral aliphatic amino acid that contains a hydroxyl group. It is polar but uncharged and is abundant in silk fibroin and silk proteins. It is classified as a serine family amino acid, a proteinogenic amino acid, an L-alpha-amino acid, and a serine.
Serine is a chiral amino acid, existing in both L- and D-forms. Only the L-form is naturally occurring in proteins, while the D-form is synthesized from L-serine through the action of serine racemase. It is classified as a polar, uncharged (at physiological pH), aliphatic amino acid. Serine is found in a zwitterionic state at physiological pH (~7.4), where the side chain is uncharged and the amino group is protonated (-NH₃⁺) while the carboxyl group is deprotonated (-COO⁻). This structure adds to serine's significance in cellular operations by enabling it to take part in processes like phosphorylation and enzyme catalysis.
Historical Discovery
Serine was first obtained from silk protein, a particularly rich source, in 1865 by Emil Cramer. It was first isolated in 1865 from the sulfuric acid hydrolysis solution of silk. It was one of the last of the common proteinogenic amino acids to be isolated and characterized from natural materials.
Essential vs. Non-Essential Classification
In humans, serine is a nonessential amino acid that can be easily derived from glycine. A non-essential amino acid is an amino acid that can be synthesized from central metabolic pathway intermediates in humans and is not required in the diet. Like all the amino acid building blocks of protein and peptides, serine can become essential under certain conditions, and is thus important in maintaining health and preventing disease.
The classification of L-serine as a non-essential amino acid has come to be considered as conditional, since vertebrates such as humans cannot always synthesize optimal quantities over entire lifespans. Once considered a non-essential amino acid, L-serine is now recognized as conditionally essential in the brain, orchestrating a complex network of metabolic and signalling pathways. The brain is a serine-limited environment due to the low permeability of serine enantiomers (as well as glycine) across the blood-brain barrier; it is for this reason that L-serine is better considered a conditionally essential amino acid for CNS development and function.
Natural Dietary Sources
Serine can be obtained from various sources, including soybeans, brewing yeast, dairy products, eggs, fish, whey protein, legumes, meat, nuts, seafood, seeds, and whole grains. It is abundant in soy products, some edible seaweeds, sweet potatoes, eggs, and meat.
Endogenous Biosynthesis
L-serine may be derived from four possible sources: dietary intake; biosynthesis from the glycolytic intermediate 3-phosphoglycerate; from glycine; and by protein and phospholipid degradation. In the first biosynthetic step of serine biosynthesis, the NAD⁺-dependent enzyme 3-phosphoglycerate dehydrogenase (PHGDH) converts 3-phosphoglycerate into 3-phosphohydroxypyruvate, which in turn is converted to 3-phosphoserine by phosphoserine aminotransferase (PSAT). Then the phosphoserine phosphatase (PSPH) removes the phosphate group from phosphoserine to form L-serine. Since some L-serine is produced by astrocytes in the brain, it is considered by some authorities to be a non-essential amino acid, although certain genetic diseases indicate that L-serine is a constituent essential amino acid.
Common Forms and Preparations
Currently, the industrial production methods for serine typically include fermentation, protein hydrolysis extraction, chemical synthesis, and enzymatic processes. L-serine is considered as GRAS (generally recognized as safe) by the FDA and has been approved as a normal food additive under CFR 172.320. It is widely sold as a dietary supplement. In clinical research and therapeutic contexts, L-serine has been administered as an oral powder dissolved in liquid, in divided daily doses.
2. Traditional and Historical Use
L-serine does not carry a documented tradition of use as an isolated ingredient in classical herbal or ethnomedicinal systems, because it was only identified as a distinct chemical entity in 1865 and its structural characterization and biosynthesis were elucidated over the subsequent century. As a ubiquitous component of dietary protein, it has been consumed throughout human history in protein-containing foods. L-serine has been used for the treatment of serine deficiency disorders and as a neuroprotective substance for decades. Its documented medicinal use as a supplement is entirely a modern clinical development, arising from biochemical and genetic research in the late 20th and early 21st centuries.
L-serine is currently prescribed, sometimes in combination with glycine, for the treatment of two different genetic neurological diseases that result in L-serine deficiency, e.g., 3-phosphoglycerate dehydrogenase deficiency and 3-phosphoserine phosphatase deficiency. The application of supplemental L-serine as a pharmacological agent for neurological conditions emerged primarily from research in the 1990s following the characterization of inborn errors of serine biosynthesis.
3. Key Constituents and Mechanisms of Action
Role in Protein Biosynthesis and Phosphorylation
L-serine has exceptional importance in metabolism of all nutrients and in a broad range of cellular functions. L-serine is a substrate for glucose and protein synthesis, and it is a building block of phospholipids, particularly phosphatidylserine (PS), and sphingolipids (SL), such as ceramides, phosphosphingolipids, and glycosphingolipids, which are highly concentrated in all cell membranes. L-serine residues in proteins serve, along with those of threonine, tyrosine, and histidine, as key sites for phosphorylation necessary for proper protein folding and functionality.
One-Carbon Metabolism, Folate, and Methylation
L-serine provides carbon units to the one-carbon metabolism, supporting nucleotide synthesis and methylation reactions, and serves as a precursor for phosphatidylserine and sphingolipids. L-serine plays crucial roles in glutathione and heme metabolism and interfaces with mitochondrial one-carbon pathways, thereby linking it to energy production, redox homeostasis, and epigenetic regulation. L-serine is important also in the synthesis of glycine and in folate and methionine cycles, in synthesis of sulphur-containing amino acids, and in neurotransmission.
Sphingolipid Biosynthesis and the Serine Palmitoyltransferase Pathway
Serine palmitoyltransferase (SPT) condenses L-serine with palmitoyl-CoA to synthesize sphingolipids including ceramides. This reaction is the rate-limiting and first committed step in the de novo synthesis of all sphingolipids. When L-serine is limiting, SPT can use alternative substrates, producing atypical and neurotoxic molecules. L-serine deficiency is associated with impaired function of the nervous system, primarily due to abnormal metabolism of phospholipids and sphingolipids, particularly increased synthesis of deoxysphingolipids.
D-Serine and NMDA Receptor Co-agonism
L-serine's conversion into glycine and D-serine further supports neurotransmission, synaptic plasticity, and cognitive functions. D-serine, synthesized from L-serine by the enzyme serine racemase, is an endogenous co-agonist at the glycine-binding site of N-methyl-D-aspartate (NMDA) receptors. Since some L-serine is produced by astrocytes in the brain, it is considered by some authorities to be a non-essential amino acid. The conversion of supplemental L-serine to D-serine in the brain has been proposed as one mechanism by which oral L-serine supplementation may influence NMDA receptor function.
Precursor for Cysteine, Choline, and Purines
L-serine serves as an important precursor for the synthesis of choline and cysteine in the body. L-serine is directly involved in the biosynthesis of purines, pyrimidines, and other amino acids.
Neuroprotective Mechanisms
Growing evidence has suggested that L-serine regulates the release of several cytokines in the brain under some neuropathological conditions to recover cognitive function, improve cerebral blood flow, inhibit inflammation, promote remyelination and exert other neuroprotective effects on neurological injury. Autophagy impairment or failure is characteristic of many neurodegenerative diseases; thus, activation of autophagic-lysosomal proteolysis may contribute to the neuroprotective effect of L-serine, which has been reported in cell culture and human clinical trials.
4. Scientific Evidence by Area of Use
4.1 Primary Serine Biosynthesis Defects (3-PGDH Deficiency and Related Disorders)
This area represents the most established clinical application of L-serine supplementation, where the evidence base is strongest.
3-phosphoglycerate dehydrogenase (PHGDH) deficiency is a disorder of L-serine biosynthesis that is characterized by congenital microcephaly, psychomotor retardation, and seizures. The landmark initial case series established both the diagnosis and the response to treatment. Treatment with oral serine in the youngest patient significantly increased cerebrospinal fluid serine and abolished the convulsions. Serine concentrations were markedly decreased in the cerebrospinal fluid of two brothers with congenital microcephaly, profound psychomotor retardation, hypertonia, epilepsy, growth retardation, and hypogonadism.
Treatment with oral L-serine abolished seizures and improved psychomotor development, hyperexcitability, head growth, cortical and subcortical hypotrophy, and hypomyelination of the brain on MRI scans in a patient with 3-PGDH deficiency presenting as West syndrome. Case reports have also described milder presentations: a very mild form of genetically confirmed 3-PGDH deficiency was reported in two siblings with juvenile onset of absence seizures and mild developmental delay. Amino acid analysis showed serine values in CSF and plasma identical to what is observed in the severe infantile form. Both patients responded favourably to relatively low dosages of serine supplementation with cessation of seizures, normalisation of their EEG abnormalities and improvement of well-being and behaviour.
Clinical experience with the treatment of 3-phosphoglycerate dehydrogenase deficiency, a rare inherited disorder of serine synthesis, is scarce. A favourable response to combined serine and glycine supplementation has been reported. However, high-dose serine therapy also carries specific risks in this population: in one patient, feeding difficulties prompted temporary treatment with high-dose serine (1400 mg/kg/day). An arrest of head growth then occurred but could be reversed by reducing the serine supply.
Evidence assessment: Robust for the specific indication of primary serine biosynthesis defects. The evidence is based on case series and case reports — the rarity of the disorders precludes large randomised trials — but mechanistic plausibility is very high and clinical responses are well-documented and reproducible across multiple reports.
4.2 Hereditary Sensory and Autonomic Neuropathy Type 1 (HSAN1)
Hereditary sensory and autonomic neuropathy type 1 (HSAN1) causes sensory loss that predominantly affects the lower limbs, often preceded by hyperpathia and spontaneous shooting or lancinating pain. It is caused by several missense mutations in the genes encoding 2 of the 3 subunits of the enzyme serine palmitoyltransferase (SPT). The mutant forms of the enzyme show a shift from their canonical substrate L-serine to the alternative substrate L-alanine. This shift leads to increased formation of neurotoxic deoxysphingolipids (dSLs).
An initial translational study demonstrated that in mice bearing a transgene expressing the C133W SPTLC1 mutant linked to HSAN1, a 10% L-serine-enriched diet reduced dSL levels. This was subsequently extended to a human pilot study. L-serine has been shown to reduce the production of neurotoxic deoxysphingolipids that are responsible for hereditary sensory autonomic neuropathy type 1, and has shown encouraging results in a pilot clinical trial.
A formal randomised trial then followed: in a randomized, placebo-controlled, parallel-group trial with open-label extension, patients aged 18–70 years with symptomatic HSAN1 were randomized to L-serine (400 mg/kg/day) or placebo for 1 year. All participants received L-serine during the second year. The primary outcome measure was the Charcot-Marie-Tooth Neuropathy Score version 2 (CMTNS). In this clinical trial, L-serine supplementation clearly reduced levels of the toxic deoxysphingoid bases in patients. L-serine helped with sensory symptoms, and appeared to increase arm and leg strength in people who took it.
L-serine has also been investigated in HSAN1C (caused by SPTLC2 mutations). Hereditary sensory neuropathy type 1 (HSAN1) may be the first genetic neuropathy amenable to a specific mechanism-based treatment, as L-serine supplementation can be used to lower the neurotoxic levels of 1-deoxysphingolipids (1-deoxySL) that cause the neurodegeneration. One patient underwent a 52-week treatment in which the L-serine dose was titrated up to 400 mg/kg/day. She was followed up by repeated clinical examination, nerve conduction testing, and skin biopsies to document effects on small nerve fibers.
Evidence assessment: Moderately strong for the specific biomarker outcome (reduction of 1-deoxysphingolipids), supported by a randomised controlled trial in a rare disease. Clinical functional outcomes showed trends but sample sizes were small. The mechanism is well-characterised, making this one of the better-supported applications of L-serine supplementation.
4.3 Amyotrophic Lateral Sclerosis (ALS)
Interest in L-serine for ALS was triggered by the observation that the neurotoxin β-methylamino-L-alanine (L-BMAA), produced by cyanobacteria and bioaccumulated in some food chains, may be a risk factor for ALS and other neurodegenerative diseases. L-serine has been reported to function as a competitive inhibitor of L-BMAA toxicity in cell cultures.
A phase I human clinical trial for safety of L-serine in ALS patients was completed and published in 2016 (NCT01835782, Levine et al. 2016). Patients (n=20) with an ALSFRS-R score >25 and a FVC score ≥60% predicted were randomly assigned to four different oral twice-daily dose regimens (0.5, 2.5, 7.5, or 15 g/dose) for six months. Two of the patients withdrew with gastrointestinal problems, but otherwise L-serine was well tolerated. No other adverse effects were noted among the remaining study participants, and no changes were seen throughout the trial in routine blood studies.
Analysis of the ALSFRS-R slopes indicated that ALS patients taking L-serine had a reduction in rate of functional loss compared to historical ALS control patients. Sample sizes within a dose group are small, and so a Phase II trial of L-serine for 66 ALS patients was planned to see if this preliminary indication of efficacy can be replicated in a larger group. What can be concluded from the Phase I data is that L-serine at doses up to 30 g/day is safe for ALS patients.
Evidence assessment: Preliminary only. The Phase I trial established safety up to 30 g/day and generated a preliminary, exploratory signal of potential benefit. It was not powered to demonstrate efficacy, and comparison to historical controls is methodologically limited. Larger placebo-controlled Phase II/III trials are required before conclusions on efficacy can be drawn.
4.4 GRIN-Related Neurodevelopmental Disorders
A chronic L-serine dietary supplement of 500 mg/kg/per day in a 5-year-old GRIN2B patient was described, with notable improvements in motor and cognitive performance and communication after 11 and 17 months of L-serine dietary supplementation. These data suggest that L-serine supplementation might ameliorate GRIN2B-related severe encephalopathy and other neurological conditions caused by glutamatergic signaling deficiency.
Dietary supplementation of L-serine results in increased D-serine plasma levels and potentiates NMDA receptors, leading to NMDA receptor functionality increase and hypofunctionality rescue, as shown in a pilot study. Oral L-serine supplementation has been associated with clinical improvement in small case series and early-phase clinical studies involving individuals with GRIN-related neurodevelopmental disorders due to loss-of-function variants. However, systematic evidence from randomised, blinded studies remains limited, particularly given the rarity and phenotypic heterogeneity of these disorders.
A study was designed to evaluate the clinical effect and safety of L-serine supplementation using an aggregated series of randomised, double-blind, placebo-controlled n-of-1 trials. The n-of-1 approach allows each participant to serve as their own control and is well suited to rare diseases with substantial inter-individual variability. By aggregating data from multiple single-patient trials using Bayesian hierarchical models, the study aims to provide both individual-level and population-level estimates of treatment effect.
Evidence assessment: Currently preliminary and based on case reports/series. Mechanistic rationale is plausible, but confirmatory randomised controlled trials are ongoing or planned and results are not yet available at scale.
4.5 Diabetic Neuropathy and Diabetes Mellitus
L-serine is classified as a non-essential amino acid; however, L-serine is indispensable having a central role in a broad range of cellular processes. Growing evidence suggests a role for L-serine in the development of diabetes mellitus and its related complications, with L-serine being positively correlated to insulin secretion and sensitivity. L-serine metabolism is altered in type 1, type 2, and gestational diabetes, and L-serine supplementations improve glucose homeostasis and mitochondrial function, and reduce neuronal death.
It is supposed that altered synthesis of sphingolipids plays a key role, especially through increased levels of neurotoxic deoxysphingolipids (DSLs). In addition to the role in pathogenesis of neuropathy, it has been shown that DSLs are cytotoxic for pancreatic β-cells, suggesting that their increased levels may contribute to impaired glucose homeostasis and pathogenesis of diabetes itself. Recently, DSLs have been suggested as a predictive biomarker for type 2 diabetes mellitus.
There are several studies reporting that L-serine supplementation reduces DSL concentration and improves glucose homeostasis and signs of neuropathy in diabetes. However, long-term animal data present a nuanced picture: functional neuropathy and sensory modalities were significantly improved in L-serine-treated diabetic mice well into advanced stages of disease. However, structural assessments revealed prominent axonal degeneration, apoptosis and Schwann cell pathology, suggesting that neuropathy was ongoing. Hyperglycemia and dyslipidemia persisted during the study. Results demonstrate that despite significant functional improvements, L-serine does not prevent chronic degenerative changes specifically at the structural level, pointing to other processes such as oxidative damage and hyperglycemia that persist despite 1-deoxySL reduction.
Researchers have noted it is premature to advise people with diabetes to take serine supplements to prevent neuropathy. "You would likely need to take a lot to make a difference, and not everyone needs extra serine." More time is needed to understand serine physiology in humans and explore potential downsides to supplementation.
Evidence assessment: Largely preclinical (cell culture and animal models), with indirect support from mechanistic human studies on sphingolipid biochemistry. No dedicated large-scale randomised clinical trial in diabetic neuropathy has been completed. Evidence is currently insufficient to support clinical recommendations.
4.6 Alzheimer's Disease and Other Neurodegenerative Conditions
L-serine is a naturally occurring dietary amino acid that has recently received renewed attention as a potential therapy for the treatment of amyotrophic lateral sclerosis (ALS), Alzheimer's disease (AD), hereditary sensory autonomic neuropathy type I (HSAN1), and sleep induction and maintenance. Dietary supplementation with L-serine restores both deficits of L-serine and D-serine in the AD mouse model. Serine is currently being tested in clinical trials for its safety and efficacy in treating macular telangiectasia and Alzheimer's disease.
L-serine has also been investigated for use in treating epilepsy, schizophrenia, psychosis, and Alzheimer's disease as well as other neurological diseases. Much of this evidence, however, remains at the preclinical or very early clinical stage.
Evidence assessment: Highly preliminary for Alzheimer's disease and other neurodegenerative conditions outside of the established genetic indications. Existing human evidence is limited to Phase I safety data and animal model studies. Clinical phase II trials are reportedly in progress.
4.7 Hyperhomocysteinemia
Therapeutic benefits of L-serine have been reported in primary disorders of serine metabolism, diabetic neuropathy, hyperhomocysteinemia, and amyotrophic lateral sclerosis. The metabolic rationale relates to L-serine's role in the methionine-folate cycle: when L-serine is deficient, homocysteine may not be efficiently re-methylated or transsulfurated, leading to accumulation. Decreased L-serine levels may also play a role in elevated homocysteine levels, routinely observed in diabetic patients.
Evidence assessment: Mechanistically plausible. The evidence for benefit from supplemental L-serine in hyperhomocysteinemia is largely indirect and biochemical. No large randomised trials specifically targeting this indication with L-serine have been identified in the peer-reviewed literature.
5. Body Systems and Health Areas Associated with L-Serine
- Central Nervous System: L-serine's conversion into glycine and D-serine supports neurotransmission, synaptic plasticity, and cognitive functions. Throughout the lifespan, L-serine and its derivatives contribute to maintaining neuronal and glial homeostasis.
- Peripheral Nervous System: L-serine supplementation can be used to lower the neurotoxic levels of 1-deoxysphingolipids that cause neurodegeneration in hereditary sensory neuropathies.
- Metabolic System: Growing evidence suggests a role for L-serine in the development of diabetes mellitus and its related complications, with L-serine being positively correlated to insulin secretion and sensitivity. L-serine metabolism is altered in type 1, type 2, and gestational diabetes.
- Cell Membrane Integrity: L-serine serves as a precursor for phospholipids (e.g., phosphatidylserine) and sphingolipids (e.g., ceramides, sphingomyelin, and glycosphingolipids), which are integral components of cell membranes.
- Redox and Antioxidant Systems: L-serine plays crucial roles in glutathione and heme metabolism and interfaces with mitochondrial one-carbon pathways, thereby linking it to energy production, redox homeostasis, and epigenetic regulation.
- Renal System (as a site of metabolism): The kidney is a significant site of serine catabolism and interconversion with glycine; use of L-serine and its metabolic products has been investigated for the therapy of renal diseases, central nervous system injury, and in a wide range of neurological and psychiatric disorders.
- Immune and Inflammatory Pathways: L-serine has been shown to attenuate the inflammatory response, which is usually associated with oxidative stress during aging. The concentrations of inflammatory cytokines and the expression of NFκB decreased in animal hypothalami after L-serine administration, indicating that the NFκB pathway plays an important role in mediating the preventive effects of L-serine against increased inflammation.
6. Dosage Forms and Dosages Reported in Studies
L-serine is administered as an oral supplement, typically as a crystalline amino acid powder dissolved in water or other liquids. The following dosages have been specifically reported in published clinical and research contexts:
- Typical dietary intake: The typical diet provides about 3.5–8 grams daily.
- Phase I ALS trial (Levine et al., 2016/2017): A randomized, double-blind phase I clinical trial for six months on the effects of oral L-serine was conducted in patients with ALS with a diagnosis of probable or definite ALS, age 18–85 years, disease duration of less than three years and forced vital capacity (FVC) ≥60%. Patients were randomly assigned to four different oral twice-daily dose regimens (0.5, 2.5, 7.5, or 15 g/dose), corresponding to total daily doses of 1, 5, 15, and 30 g/day.
- HSAN1 randomised trial (Fridman et al., 2019): Patients aged 18–70 years with symptomatic HSAN1 were randomized to L-serine (400 mg/kg/day) or placebo for 1 year.
- HSAN1C case study: A patient underwent a 52-week treatment in which the L-serine dose was titrated up to 400 mg/kg/day.
- GRIN2B encephalopathy case: A chronic L-serine dietary supplement of 500 mg/kg/per day was used in a 5-year-old GRIN2B patient.
- 3-PGDH deficiency (high-dose case observation): A patient was temporarily treated with high-dose serine (1400 mg/kg/day), during which an arrest of head growth occurred but was reversed by reducing the serine supply. This case illustrates risks at very high doses in paediatric patients.
- Subchronic preclinical reference dose: A subchronic oral toxicity study was conducted in Sprague-Dawley rats administered L-serine once daily by gavage at dose levels of 0, 500, 1500, and 3000 mg/kg body weight/day for 13 weeks. Daily clinical signs, body weight, and food consumption were not affected. There were no treatment-related adverse effects on urinalysis, hematology, serum biochemistry, organ weights, or gross and histopathological examination. The no-observed-effect level (NOEL) for L-serine was 3000 mg/kg bw/day for both genders.
7. Safety Considerations and Interactions
Regulatory Safety Status
L-serine is considered GRAS (generally recognized as safe) by the FDA and has been approved as a normal food additive under CFR 172.320. It is widely sold as a dietary supplement. No adverse incidents have been recorded by the FDA from its use.
Tolerability in Human Clinical Trials
In the Phase I ALS trial, patients were given either 1, 5, 15, or 30 g/day for six months. Very few side-effects were reported (bloating, nausea, and loss of appetite). Unlike D-serine, L-serine represents a more favorable therapeutic option because it is considered to be safe by the Food and Drug Administration. L-serine has also been approved as a routine food additive, it is widely sold as a dietary supplement, and is well-tolerated, even at high doses.
D-Serine and Nephrotoxicity (Species-Specific Distinction)
The nephrotoxicity concern is primarily associated with D-serine, not L-serine. When D-serine doses >500 mg/kg are used in rats, nephrotoxicity, manifesting as an acute tubular necrosis syndrome seen within hours of administration, is highly common. In other species, however, D-serine induced nephrotoxicity has not been reported, even in other rodent species such as mice and rabbits. Even in rats, D-serine-related toxicity is dose dependent and reversible. Historical animal studies involving the racemic D,L-serine mixture should be interpreted with caution when extrapolating to the L-enantiomer. Slow and weak diffusion through the blood-brain barrier and potential nephrotoxicity have limited the clinical use of D-serine.
Subchronic Preclinical Safety
A subchronic oral toxicity study in Sprague-Dawley rats found no treatment-related adverse effects on urinalysis, hematology, serum biochemistry, organ weights, gross and histopathological examination at any tested dose. The no-observed-effect level (NOEL) for L-serine was 3000 mg/kg bw/day for both genders.
Risks in Paediatric Serine Biosynthesis Disorders at Very High Doses
In a patient with 3-PGDH deficiency, temporary treatment with high-dose serine (1400 mg/kg/day) was associated with an arrest of head growth, which was reversed by reducing the serine supply. In both children undergoing serine therapy, treatment was associated with decreased concentrations of methionine and isoleucine, indicating that supra-physiological doses of L-serine may competitively alter the plasma concentrations of other amino acids.
Effect on Other Amino Acid Levels
Some essential and nonessential amino acids, including glycine, L-cysteine, L-alanine, and L-threonine, share structural similarities with L-serine. Prolonged aberrant amino acid homeostasis may therefore lead to differential substrate usage owing to minor differences in their chemical potential. High-dose supplementation carries a theoretical risk of displacing or altering the plasma balance of structurally similar amino acids.
Conditional Essentiality and Deficiency Risk
Circulating L-serine and glycine levels, their turnover, and their biomarkers vary in the context of disease states and across the human population. Low L-serine levels drive specific disease comorbidities through their impact on different cell types and biochemical pathways. Whether L-serine may sometimes be considered a conditionally essential amino acid is potentially true in selected cases or patients. However, by and large, most people take in and retain adequate L-serine for survival.
Interactions
L-serine is important in the synthesis of glycine and in folate and methionine cycles, in synthesis of sulphur-containing amino acids, and in neurotransmission. Because of its involvement in the methionine-folate one-carbon cycle, very high supplemental doses could theoretically interact with folate, vitamin B12, vitamin B6, and methionine metabolism. No specific drug-supplement interactions for L-serine have been formally documented in the peer-reviewed clinical literature. Decreased L-serine levels may also play a role in elevated homocysteine levels routinely observed in diabetic patients, suggesting an interplay between L-serine status and homocysteine-related cardiovascular risk.
Safety of L-serine has been demonstrated in an FDA-approved human Phase I clinical trial with ALS patients (ClinicalTrials.gov identifier: NCT01835782), but treatment of ALS symptoms has yet to be definitively shown.
References
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