Vitamin B9 (L-Methylfolate / 5-MTHF)
Also known as: Folate, Folic Acid (as a general term for B9), 5-MTHF, L-5-Methyltetrahydrofolate, Metafolin, Deplin
L-Methylfolate is the principal circulating form of folate and the only form that can cross the blood-brain barrier. It plays a critical role as a coenzyme in one-carbon metabolism, particularly in the methylation cycle. Its direct bioavailability makes it a preferred supplemental form, especially when addressing folate deficiencies or supporting processes requiring efficient methylation, such as neurotransmitter synthesis and homocysteine regulation. Research indicates its efficacy in supporting mood, cardiovascular health, and cognitive function, particularly in populations with impaired folate metabolism.
Last reviewed: 2026-04-22 · 4 indexed studies
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Overview
L-Methylfolate (5-MTHF) is the biologically active, methylated form of folate (Vitamin B9). Unlike synthetic folic acid, 5-MTHF does not require enzymatic conversion by the dihydrofolate reductase (DHFR) enzyme, making it directly usable by the body. This is particularly relevant for individuals with genetic polymorphisms (e.g., MTHFR) that impair folic acid metabolism. Folate is essential for numerous physiological processes, including DNA synthesis and repair, methylation reactions, and the metabolism of homocysteine.
Mechanism & Function
L-5-Methylfolate · C₂₀H₂₅N₇O₆ — source: PubChem CID 444412
Pale cream crystalline active folate. Bypasses MTHFR conversion — preferred for variant carriers.
- Capsule
- Tablet
- Sublingual
Capsule is generally preferred for bioavailability or efficacy.
Mechanism of Action
L-Methylfolate acts as a methyl donor in various biochemical reactions, primarily by donating its methyl group to homocysteine to form methionine, a precursor to S-adenosylmethionine (SAMe). SAMe is a universal methyl donor involved in the synthesis of neurotransmitters (e.g., serotonin, dopamine, norepinephrine), phospholipids, and myelin. It's also crucial for DNA synthesis and repair, and cell division.
Physiological Role
Folate's primary physiological role is to act as a coenzyme in the transfer of one-carbon units in metabolic pathways. This includes participation in the synthesis of purines and pyrimidines (components of DNA and RNA), the interconversion of amino acids, and the methylation cycle pivotal for neurotransmitter synthesis and detoxification. Optimal folate status is crucial for erythropoiesis, neurological function, and fetal development.
Primary Pathways
Performance / Health Relevance
While not directly enhancing acute physical performance, L-Methylfolate supports overall physiological function that indirectly impacts performance. Its role in homocysteine metabolism can contribute to cardiovascular health, which is foundational for endurance. Furthermore, its involvement in neurotransmitter synthesis may support cognitive function and mood, which are critical for focus and mental resilience in demanding situations. For athletes, ensuring optimal folate status supports red blood cell production and cellular repair mechanisms.
Evidence Review
Compare Vitamin B9 (Folate) Forms
Full comparison2 vitamin b9 (folate) forms are indexed. Bioavailability, clinical evidence, and best-use cases differ meaningfully between them.
| Form | Evidence |
|---|---|
Vitamin B9 (L-Methylfolate / 5-MTHF)This page L-methylfolate is directly bioactive, bypassing the need for conversion. This provides superior bioavailability compared to synthetic folic acid for individuals with MTHFR polymorphisms. | 75/100 |
| Vitamin B9 (Folic Acid) Synthetic folic acid has nearly 100% bioavailability when consumed on an empty stomach, and about 85% with food. Natural food folates have about 50% bioavailability. | 65/100 |
Practical Use & Dosage
- Minimum Effective Dose
- 200 mcg DFE
- Optimal Range
- 400-800 mcg DFE daily (or 1000-5000 mcg for specific clinical applications under medical supervision)
- Upper / Caution Level
- No observed adverse effect level (NOAEL) for L-methylfolate itself; synthetic folic acid has a UL of 1000 mcg.
- Timing
- Can be taken any time of day, with or without food. Some prefer morning.
- Best Format
- Capsules or tablets. Oral drops for children or those with swallowing difficulties.
- Bioavailability
- L-methylfolate is directly bioactive, bypassing the need for conversion. This provides superior bioavailability compared to synthetic folic acid for individuals with MTHFR polymorphisms.
- Absorption Considerations
- Generally well-absorbed. Co-ingestion with B12 is often recommended as folate metabolism is intertwined with B12.
Safety & Interactions
Side Effects
- •Rarely, mild gastrointestinal upset
- •Insomnia or irritability (at high doses in sensitive individuals, often related to increased methylation)
Contraindications
- Undiagnosed pernicious anemia (due to masking B12 deficiency symptoms)
- Bipolar disorder (high doses may exacerbate symptoms in some individuals)
Drug Interactions
- •Methotrexate (folate antagonist)
- •Antiepileptic drugs (phenytoin, carbamazepine, valproate) - may reduce drug levels or increase seizure risk; close monitoring advised.
- •Pyrimethamine
- •Certain antibiotics (e.g., trimethoprim)
Who Should Avoid
- •Individuals with undiagnosed Vitamin B12 deficiency
- •Individuals with certain types of cancer (as folate supports cell division, though evidence is complex)
- •Individuals with known hypersensitivity to folate
Monitoring
In cases of high-dose supplementation, especially in individuals with MTHFR polymorphisms or mood disorders, monitoring of homocysteine levels and B12 status is advisable. Initial mood changes (e.g., anxiety) can occur, adjusting dose may be necessary.
Frequently Asked Questions
Auto-generated from indexed evidence — dosage, safety, interactions, and more.
When is Vitamin B9 (L-Methylfolate / 5-MTHF) typically used or indicated?
Vitamin B9 (L-Methylfolate / 5-MTHF) is most commonly used for: Mood support, Cardiovascular health, Cognitive function, Pregnancy (neural tube defect prevention), Homocysteine reduction. Folate's primary physiological role is to act as a coenzyme in the transfer of one-carbon units in metabolic pathways. This includes participation in the synthesis of purines and pyrimidines (components of DNA and RNA), the interconversion of amino acids, and the methylation cycle pivotal for neurotransmitter synthesis and detoxification. Optimal folate status is crucial for erythropoiesis, neurological function, and fetal development.
How does Vitamin B9 (L-Methylfolate / 5-MTHF) work?
L-Methylfolate acts as a methyl donor in various biochemical reactions, primarily by donating its methyl group to homocysteine to form methionine, a precursor to S-adenosylmethionine (SAMe). SAMe is a universal methyl donor involved in the synthesis of neurotransmitters (e.g., serotonin, dopamine, norepinephrine), phospholipids, and myelin. It's also crucial for DNA synthesis and repair, and cell division.
What is the recommended dose of Vitamin B9 (L-Methylfolate / 5-MTHF)?
The optimal range is 400-800 mcg DFE daily (or 1000-5000 mcg for specific clinical applications under medical supervision). with a minimum effective dose of 200 mcg DFE. Best taken: Can be taken any time of day, with or without food. Some prefer morning.. Upper / caution level: No observed adverse effect level (NOAEL) for L-methylfolate itself; synthetic folic acid has a UL of 1000 mcg..
What are the side effects of Vitamin B9 (L-Methylfolate / 5-MTHF)?
Reported side effects include: Rarely, mild gastrointestinal upset; and Insomnia or irritability (at high doses in sensitive individuals, often related to increased methylation). Monitoring: In cases of high-dose supplementation, especially in individuals with MTHFR polymorphisms or mood disorders, monitoring of homocysteine levels and B12 status is advisable. Initial mood changes (e.g., anxiety) can occur, adjusting dose may be necessary.
Does Vitamin B9 (L-Methylfolate / 5-MTHF) interact with medications?
Known or theoretical interactions: Methotrexate (folate antagonist); Antiepileptic drugs (phenytoin, carbamazepine, valproate) - may reduce drug levels or increase seizure risk; close monitoring advised.; Pyrimethamine; and Certain antibiotics (e.g., trimethoprim). Always check with a clinician before combining with prescription medication.
Who should avoid Vitamin B9 (L-Methylfolate / 5-MTHF)?
Vitamin B9 (L-Methylfolate / 5-MTHF) is generally not recommended for: Individuals with undiagnosed Vitamin B12 deficiency; Individuals with certain types of cancer (as folate supports cell division, though evidence is complex); Individuals with known hypersensitivity to folate; Undiagnosed pernicious anemia (due to masking B12 deficiency symptoms); and Bipolar disorder (high doses may exacerbate symptoms in some individuals).
How strong is the evidence for Vitamin B9 (L-Methylfolate / 5-MTHF)?
Evidence level: Strong (overall score 75/100), based on 4 indexed studies on SuppIndex.
Research & References (4)
L-methylfolate as an adjunct to antidepressants in the treatment of major depressive disorder: a literature review
This review evaluated the efficacy of L-methylfolate as an adjunctive treatment for major depressive disorder (MDD). It synthesized findings from several studies, noting that L-methylfolate, particularly at higher doses, showed benefit in improving antidepressant response, especially in patients with low folate levels or MTHFR gene polymorphisms. The mechanism is linked to its role in neurotransmitter synthesis.
The effect of L-methylfolate on homocysteine levels and endothelial function in patients with coronary artery disease: A randomized, placebo-controlled trial
This study investigated the effects of L-methylfolate on homocysteine levels and endothelial function in patients with stable coronary artery disease. Elevated homocysteine is a known risk factor for cardiovascular disease. The study aimed to see if direct folate supplementation could improve these markers.
Meta-analysis of folic acid and risk of neural tube defects
While this meta-analysis focuses on folic acid, its findings are highly relevant to L-methylfolate due to the latter's superior bioavailability. It reviewed numerous studies on the efficacy of periconceptional folic acid supplementation in preventing neural tube defects (NTDs).
Folate and MTHFR gene polymorphism: an integral role in neurocognitive function and mental health
This review explores the intricate relationship between folate, the MTHFR gene polymorphism, and their impact on various aspects of neurocognitive function and mental health. It synthesizes evidence concerning the role of folate in brain health and how genetic variations affect this.
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Research Overview
Strong EvidenceCite this ingredient
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Stable URL
https://thesuppindex.com/ingredients/vitamin-b9-l-methylfolate-5-mthf
SuppIndex. (2026). Vitamin B9 (L-Methylfolate / 5-MTHF): Evidence summary, dosage and clinical studies. Retrieved October 23, 2026, from https://thesuppindex.com/ingredients/vitamin-b9-l-methylfolate-5-mthf
Based on 4 indexed studies · Evidence level: Strong.
Goal Ratings
Stack Compatibility
Highly compatible with B vitamins, especially B12 and B6, which are synergistic in the methylation cycle. Also compatible with omega-3 fatty acids, magnesium, and other nutrients supporting neurological health.