Folate · Vitamin B9
Evidence Fact Sheet
Folic Acid · 5-MTHF
Folate (vitamin B9; folic acid / 5-MTHF) is a one-carbon metabolism cofactor for DNA synthesis and methylation. Randomized evidence supports periconceptional supplementation for neural tube defect risk reduction and homocysteine lowering; trials show null effects on cognitive decline and on overall cancer incidence. Authorized health claims in the US, EU, and Brazil.
Also known as: Folic acid · 5-methyltetrahydrofolate · 5-MTHF · Vitamin B9 · L-methylfolate calcium
Overview
Folate (vitamin B9) is a water-soluble essential vitamin available as folic acid or as the reduced form 5-methyltetrahydrofolate (5-MTHF). It acts as a one-carbon metabolism cofactor in DNA synthesis, methylation, and amino acid metabolism, works alongside vitamin B12 in the methionine synthase reaction, and is required for neural tube closure in early embryogenesis. Typical research and supplement doses range from 400 μg/day periconceptionally up to 4 mg/day for recurrence prevention in women with a prior neural tube defect pregnancy, against an adult RDA of 400 μg DFE; a tolerable upper limit of 1000 μg/day applies to folic acid from fortified food plus supplements. Folate supplementation can mask the haematological signs of B12 deficiency, so B12 status should be considered alongside. Regulatory status is well established: FDA GRAS with an authorized neural-tube-defect health claim (21 CFR 101.79), multiple EFSA authorized claims plus a Reg 1135/2014 disease-risk-reduction claim, and ANVISA and SAMR recognition.
Mechanism of Action
One-carbon metabolism cofactor (DNA synthesis, methylation, amino acid metabolism) · Co-cofactor with B12 in methionine synthase reaction · Required for neural tube closure in early embryogenesis (closure window day 21-28 post-conception)
Body systems: Blood & Hematopoiesis · REPRODUCTIVE · Cardiovascular
Evidence-Based Benefits
Each benefit below is anchored to a specific PubMed-indexed study. Effect sizes, sample sizes, and p-values are reported as published; no values are inferred. Honest negatives and null results are kept alongside the positive findings, and disease-research populations are described as such — Folate · Vitamin B9 is not characterized as a treatment for any disease.
Neural Tube Defect Prevention (Periconceptional)
Meta-analysis supported- RR 0.34NTD recurrence · 95% CI 0.18-0.64
- 4 studies1846 births
- 7391 women5 trials total
In this Cochrane systematic review of randomized trials, periconceptional folate supplementation had a significant protective effect against recurrence of neural tube defects in women with a prior affected pregnancy. The review concluded folic acid prevents NTDs but found no clear effect on other birth defects.
Reported effect: Folic acid had a significant protective effect for reoccurrence (RR 0.34, 95% CI 0.18 to 0.64); four studies; 1846 births. 5 trials; 7391 women.
“Folic acid had a significant protective effect for reoccurrence (RR 0.34, 95% CI 0.18 to 0.64); four studies; 1846 births”
Source: PMID 26662928 · De-Regil 2015 · Cochrane Database Syst Rev
Homocysteine Lowering
Meta-analysis supported- 25%homocysteine reduction · 95% CI 23-28%
This collaborative meta-analysis of randomized trials found that dietary folic acid reduced blood homocysteine concentrations by about a quarter in Western populations, with similar effects across the 0.5-5 mg/day dose range. This supports the EFSA authorized claim that folate contributes to normal homocysteine metabolism.
Reported effect: dietary folic acid reduced blood homocysteine concentrations by 25% (95% confidence interval 23% to 28%; P < 0.001)
“dietary folic acid reduced blood homocysteine concentrations by 25% (95% confidence interval 23% to 28%; P < 0.001)”
Source: PMID 9569395 · Homocysteine Lowering Trialists' Collaboration 1998 · BMJ
Stroke and Cardiovascular Outcomes
Meta-analysis supported- RR 0.90stroke · 95% CI 0.84-0.96
- RR 0.96overall CVD · 95% CI 0.92-0.99
In this meta-analysis of 30 randomized controlled trials, folic acid supplementation was associated with a modest reduction in stroke and overall cardiovascular disease versus controls. Notably, there was no significant effect on coronary heart disease (RR 1.04, 95% CI 0.99-1.09), so the cardiovascular benefit is partial rather than uniform.
Reported effect: The pooled relative risks of folic acid supplementation compared with controls were 0.90 (95% CI 0.84-0.96; P=0.002) for stroke, 1.04 (95% CI 0.99-1.09; P=0.16) for coronary heart disease, and 0.96 (95% CI 0.92-0.99; P=0.02) for overall CVD.
“The pooled relative risks of folic acid supplementation compared with controls were 0.90 (95% CI 0.84-0.96; P=0.002) for stroke ... 1.04 (95% CI 0.99-1.09; P=0.16) for coronary heart disease ... and 0.96 (95% CI 0.92-0.99; P=0.02) for overall CVD”
Source: PMID 27528407 · Li 2016 · J Am Heart Assoc
Cognitive Decline (Honest Negative)
Null / no benefit Meta-analysis supported- SMD 0.01cognition · 95% CI -0.08 to 0.10
This meta-analysis of 9 placebo-controlled randomized trials found no effect of folic acid, with or without other B vitamins, on cognitive function within roughly 3 years of starting treatment. The standardized mean difference was essentially zero, an honest null finding for cognition.
Reported effect: The standardized mean difference in cognitive function test scores was 0.01 (95% confidence interval [95% CI], -0.08 to 0.10).
“The standardized mean difference in cognitive function test scores was 0.01 (95% confidence interval [95% CI], -0.08 to 0.10) ... Randomized trials show no effect of folic acid, with or without other B vitamins, on cognitive function within 3 years of the start of treatment.”
Source: PMID 20569758 · Wald 2010 · Am J Med
Cancer Incidence and Safety (Honest Null)
Null / no benefit Meta-analysis supported- RR 1.06overall cancer · 95% CI 0.99-1.13
- 13 trials49621 individuals
In this meta-analysis of 13 randomized trials, folic acid supplementation had no significant effect on overall cancer incidence and no significant effect on cancer of the large intestine, prostate, lung, breast, or any other specific site during the trials. This is a key safety reassurance: supplementation did not substantially raise cancer risk over the trial periods.
Reported effect: allocation to folic acid ... had no significant effect on overall cancer incidence (1904 cancers in the folic acid groups vs 1809 cancers in the placebo groups, RR 1.06, 95% CI 0.99-1.13, p=0.10)
“allocation to folic acid...had no significant effect on overall cancer incidence (1904 cancers in the folic acid groups vs 1809 cancers in the placebo groups, RR 1·06, 95% CI 0·99–1·13, p=0·10)”
Source: PMID 23352552 · Vollset 2013 · Lancet
Dosage (research context · not a recommendation)
400 μg/day periconceptional for first-occurrence NTD prevention (Czeizel 1992 PMID 1307234 NEJM RCT n = 4,156 multivitamin + 0.8 mg folic acid vs trace-element · 0 NTD vs 6 NTD); 4 mg/day for recurrence prevention in women with a prior NTD pregnancy (MRC Vitamin Study 1991 PMID 1677062 Lancet n = 1,195 completed pregnancies · 72% protective effect, RR 0.28, 95% CI 0.12-0.71); RDA 400 μg DFE for adults
Regulatory Status · 4 Markets
- US · FDA
- GRAS · DSHEA dietary supplement · 21 CFR 101.79 authorized health claim: folate + neural tube defect risk reduction (food + supplement label); 21 CFR 184.1492 folic acid food additive
- EU · EFSA
- Authorized claims Reg 432/2012 (blood formation, homocysteine, maternal tissue growth, etc.) + Commission Reg 1135/2014 implementing Reg 1924/2006 Article 14(1)(a) reduction of disease risk claim for periconceptional 400 µg folic acid lowering NTD risk; NRV 200 μg
- CN · China
- Folate is listed in the Health-Food Raw-Material Catalogue (Nutrient Supplements) under the filing/notification route; the 5-MTHF calcium salt (calcium 6S-5-methyltetrahydrofolate) holds a New Food Ingredient approval. SAMR recognized.
- BR · ANVISA
- RDC 243/2018 dietary supplement · IN 28/2018 Anexo V alegação funcional verbatim: "O ácido fólico auxilia na formação das células vermelhas do sangue." + additional homocysteine / cell division claims available when nutrient threshold met
Authorized Claims
FDA — “Healthful diets with adequate folate may reduce a woman's risk of having a child with a brain or spinal cord birth defect.” (21 CFR 101.79(d)(1)(i))
Safety
Folate supplementation can mask the haematological signs of B12 deficiency while neuropathy progresses — measure or supplement B12 alongside folate in adults > 50 or with malabsorption risk; upper limit 1000 μg/day folic acid from fortified food + supplement (excluding food folate)
Related
Goals: reproductive-health · cognitive-support · longevity-stack
Lifestyles: pregnancy · plant-based
References
PubMed-indexed citations anchoring the benefit findings above. Effect sizes are reported as published.
- PMID 26662928 · De-Regil 2015 · Cochrane Database Syst Rev — Neural Tube Defect Prevention (Periconceptional)
- PMID 9569395 · Homocysteine Lowering Trialists' Collaboration 1998 · BMJ — Homocysteine Lowering
- PMID 27528407 · Li 2016 · J Am Heart Assoc — Stroke and Cardiovascular Outcomes
- PMID 20569758 · Wald 2010 · Am J Med — Cognitive Decline (Honest Negative)
- PMID 23352552 · Vollset 2013 · Lancet — Cancer Incidence and Safety (Honest Null)
Frequently Asked Questions
1. What is the strongest evidence for folate supplementation?
The strongest randomized evidence is for periconceptional neural tube defect prevention. A Cochrane systematic review of trials in 7391 women found folic acid had a significant protective effect against NTD recurrence (RR 0.34, 95% CI 0.18-0.64). This underpins the authorized health claims for folate and neural tube defect risk reduction in the US, EU, and Brazil.
2. Does folic acid supplementation increase cancer risk?
In the largest randomized meta-analysis (13 trials, 49,621 individuals), folic acid had no significant effect on overall cancer incidence (RR 1.06, 95% CI 0.99-1.13) and no significant effect on large intestine, prostate, lung, breast, or any other specific cancer during the trials. Separately, note that folate can mask the haematological signs of B12 deficiency, so B12 status warrants attention.
Last evidence review: 2026-06-04