Vitamin B9 (Folic Acid)
Also known as: Folate, Pteroylglutamic Acid, Folacin
Folic acid is the most stable form of Vitamin B9 used in supplements and fortified foods. It is a precursor to tetrahydrofolate (THF), the active form of folate in the body. THF acts as a coenzyme in single-carbon metabolism, crucial for the synthesis of purines and pyrimidines, DNA methylation, and conversion of homocysteine to methionine. Deficiency can lead to megaloblastic anemia, developmental abnormalities, and elevated homocysteine levels, which are associated with increased cardiovascular disease risk.
Last reviewed: 2026-04-22 · 4 indexed studies
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Overview
Vitamin B9, commonly known as folic acid in its synthetic form, is a water-soluble vitamin essential for numerous bodily functions. It plays a critical role in nucleotide synthesis (DNA and RNA), amino acid metabolism, and red blood cell formation. Folate is the naturally occurring form found in foods such as leafy green vegetables, fruits, and legumes, while folic acid is typically found in fortified foods and supplements.
Mechanism & Function
Folic acid · C₁₉H₁₉N₇O₆ — source: PubChem CID 6037
Yellow-orange crystalline synthetic folate. Requires hepatic conversion to active 5-MTHF.
- Tablet
- Capsule
- Liquid
Tablet is generally preferred for bioavailability or efficacy.
Mechanism of Action
Folic acid is reduced to dihydrofolate (DHF) and then to tetrahydrofolate (THF) by the enzyme dihydrofolate reductase. THF acts as a coenzyme, accepting and donating one-carbon units in various metabolic pathways. Key reactions include the methylation of deoxyuridylate to thymidylate for DNA synthesis, and the remethylation of homocysteine to methionine via methionine synthase. Adequate folate status is critical for cell division, growth, and repair.
Physiological Role
Folate is crucial for DNA and RNA synthesis and repair, cell division, and homocysteine metabolism. It is vital during periods of rapid cell growth, such as pregnancy and infancy, to prevent developmental abnormalities like neural tube defects. It also supports red blood cell production, helping to prevent megaloblastic anemia.
Primary Pathways
Performance / Health Relevance
While not directly enhancing athletic performance, adequate folate status is essential for overall health, red blood cell production, and neurological function. Athletes, especially those with high training loads, might have increased nutrient requirements. Maintaining healthy homocysteine levels could indirectly support cardiovascular health, which is beneficial for endurance. However, direct performance benefits beyond preventing deficiency are not well-established.
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 (Folic Acid)This page 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 |
| Vitamin B9 (L-Methylfolate / 5-MTHF) 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 |
Practical Use & Dosage
- Minimum Effective Dose
- 400 mcg DFE (Dietary Folate Equivalents) for general health.
- Optimal Range
- 400-800 mcg DFE daily. For pregnant women or those planning pregnancy: 600 mcg DFE.
- Upper / Caution Level
- 1000 mcg (1 mg) of synthetic folic acid daily from supplements for adults, due to concerns about masking B12 deficiency symptoms.
- Timing
- Can be taken at any time of day, with or without food.
- Best Format
- Tablets or capsules. Bioavailability from supplements and fortified foods is generally higher than from natural food sources.
- Bioavailability
- 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.
- Absorption Considerations
- Alcohol can interfere with folate absorption and metabolism. Certain medications (e.g., methotrexate, some anticonvulsants) can also impair folate status.
Safety & Interactions
Side Effects
- •Nausea
- •Bloating
- •Irritability
- •Sleep disturbances (rare at typical doses)
Contraindications
- Individuals with an undiagnosed Vitamin B12 deficiency, as high folic acid intake can mask symptoms of B12 deficiency.
Drug Interactions
- •Methotrexate (folate antagonist)
- •Anticonvulsants (e.g., phenytoin, valproate, carbamazepine)
- •Sulfasalazine
- •Pyrimethamine
- •Trimethoprim
- •Barbiturates
Who Should Avoid
- •Individuals on specific medications that interact with folate, or those with suspected but undiagnosed B12 deficiency.
Monitoring
In cases of long-term high-dose folic acid supplementation, monitoring of Vitamin B12 status is advisable, especially in the elderly.
Frequently Asked Questions
Auto-generated from indexed evidence — dosage, safety, interactions, and more.
When is Vitamin B9 (Folic Acid) typically used or indicated?
Vitamin B9 (Folic Acid) is most commonly used for: Red blood cell formation, DNA synthesis and repair, Neural tube defect prevention, Homocysteine reduction. Folate is crucial for DNA and RNA synthesis and repair, cell division, and homocysteine metabolism. It is vital during periods of rapid cell growth, such as pregnancy and infancy, to prevent developmental abnormalities like neural tube defects. It also supports red blood cell production, helping to prevent megaloblastic anemia.
How does Vitamin B9 (Folic Acid) work?
Folic acid is reduced to dihydrofolate (DHF) and then to tetrahydrofolate (THF) by the enzyme dihydrofolate reductase. THF acts as a coenzyme, accepting and donating one-carbon units in various metabolic pathways. Key reactions include the methylation of deoxyuridylate to thymidylate for DNA synthesis, and the remethylation of homocysteine to methionine via methionine synthase. Adequate folate status is critical for cell division, growth, and repair.
What is the recommended dose of Vitamin B9 (Folic Acid)?
The optimal range is 400-800 mcg DFE daily. For pregnant women or those planning pregnancy: 600 mcg DFE.. with a minimum effective dose of 400 mcg DFE (Dietary Folate Equivalents) for general health.. Best taken: Can be taken at any time of day, with or without food.. Upper / caution level: 1000 mcg (1 mg) of synthetic folic acid daily from supplements for adults, due to concerns about masking B12 deficiency symptoms..
What are the side effects of Vitamin B9 (Folic Acid)?
Reported side effects include: Nausea; Bloating; Irritability; and Sleep disturbances (rare at typical doses). Monitoring: In cases of long-term high-dose folic acid supplementation, monitoring of Vitamin B12 status is advisable, especially in the elderly.
Does Vitamin B9 (Folic Acid) interact with medications?
Known or theoretical interactions: Methotrexate (folate antagonist); Anticonvulsants (e.g., phenytoin, valproate, carbamazepine); Sulfasalazine; Pyrimethamine; Trimethoprim; and Barbiturates. Always check with a clinician before combining with prescription medication.
Who should avoid Vitamin B9 (Folic Acid)?
Vitamin B9 (Folic Acid) is generally not recommended for: Individuals on specific medications that interact with folate, or those with suspected but undiagnosed B12 deficiency.; and Individuals with an undiagnosed Vitamin B12 deficiency, as high folic acid intake can mask symptoms of B12 deficiency..
How strong is the evidence for Vitamin B9 (Folic Acid)?
Evidence level: Moderate (overall score 65/100), based on 4 indexed studies on SuppIndex.
Research & References (4)
Folic acid and prevention of neural tube defects
This seminal randomized controlled trial demonstrated the efficacy of periconceptional folic acid supplementation in preventing neural tube defects (NTDs). Women who received folic acid had a significantly lower risk of NTD-affected pregnancies.
Folic acid supplementation for the prevention of cardiovascular disease
This meta-analysis assessed the effect of folic acid supplementation on cardiovascular disease risk. It found that folic acid supplementation effectively lowered homocysteine levels but did not consistently translate to a significant reduction in major cardiovascular events in trials without specific indication for baseline high homocysteine.
Folic acid and vitamin B12 supplementation and the risk of cancer: a systematic review and meta-analysis
This systematic review and meta-analysis investigated whether folic acid and vitamin B12 supplementation affected cancer incidence. It found no clear evidence that these supplements increase the risk of cancer at typical doses used for fortification and supplementation.
Folate supplementation and cognitive function: A systematic review and meta-analysis of randomized controlled trials
This meta-analysis synthesized evidence from RCTs to evaluate the effect of folate supplementation on cognitive function in adults. It found that folate supplementation may modestly improve some domains of cognitive function, particularly in populations with existing cognitive decline or elevated homocysteine, but not consistently in healthy individuals.
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Vitamin B9 (L-Methylfolate / 5-MTHF)
75/100L-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.
Research Overview
Moderate EvidenceCite this ingredient
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Stable URL
https://thesuppindex.com/ingredients/vitamin-b9-folic-acid
SuppIndex. (2026). Vitamin B9 (Folic Acid): Evidence summary, dosage and clinical studies. Retrieved October 23, 2026, from https://thesuppindex.com/ingredients/vitamin-b9-folic-acid
Based on 4 indexed studies · Evidence level: Moderate.
Goal Ratings
Stack Compatibility
Generally safe to stack with most vitamins and minerals. Often combined with B12, B6, and iron for synergistic effects on red blood cell health and homocysteine metabolism.