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Folic Acid (Pteroylmonoglutamic Acid)
The synthetic, fully oxidised form of vitamin B9 — the compound the neural-tube-defect prevention trials and food fortification actually used. It is NOT methylfolate: it needs dihydrofolate reductase to become active.
What the evidence says
Folic Acid doesn't have enough studies with structured effect-size data yet to pool a verdict. Browse the studies below for individual findings.
Most evidence is from high-quality meta-analyses and randomised trials published 1991–2026.
Based on 22 studies · 7 meta-analyses · 6 RCTs
Confidence
High confidenceBy outcome
5 more outcomes with fewer studies not shown.
For ONE indication — periconceptional prevention of neural tube defects — the evidence is about as strong as nutrition evidence gets: a randomised trial, a Cochrane synthesis, a US Preventive Services Task Force recommendation and mandatory national food fortification. The score is held at 8 rather than higher because folic acid's other outcomes are not evidenced here.
580 trials ongoing or recruiting · NaN completed on ClinicalTrials.gov
353 of the completed trials have posted results
Registered trials show research momentum for Folic Acid, not proof of effect — a registration is a plan, and posted results are sponsor-reported, not peer-reviewed. They are never counted toward the evidence rating above.
Browse these trials on ClinicalTrials.govClinicalTrials.gov · as of Oct 2026
Under EU law (Reg. 1924/2006), EFSA reviews whether a specific health claim for Folic Acid meets the evidence standard. These are independent regulatory decisions on claims — not studies, and never counted toward the evidence score above.
Authorised claims
“Folate contributes to maternal tissue growth during pregnancy”
“Folate contributes to normal amino acid synthesis”
“Folate contributes to normal blood formation”
“Folate contributes to normal homocysteine metabolism”
“Folate contributes to normal psychological function”
“Folate contributes to the normal function of the immune system”
“Folate contributes to the reduction of tiredness and fatigue”
“Folate has a role in the process of cell division”
Not authorised by EFSA
“Folic Acid Positive affect for protection of the lens”
“Folic acid protects the eye Folic acid important for the eye”
“Folic Acid (Vitamin B9) Contributes to healthy arteries and vessels; Helps promote heart health”
“Folic Acid B-vitamins and vitamin C are essential for the energy metabolism / the transfomation of food into energy”
“Vitamin E Vitamin C, E, A, D, B6, B12 folic acid, Selenium, Zinc, Copper and Iron are important for the immune system/natural defences”
“Not authorised” means the specific claim wording did not meet the EU’s evidence standard — often a matter of dossier or phrasing, not proof of no effect. EFSA judges marketing claims and is kept separate from our study-based evidence score.
Source: EU Register of nutrition and health claims (European Commission / EFSA) · register snapshot Feb 2013
Folic acid (pteroylmonoglutamic acid, C19H19N7O6, PubChem CID 135398658) is the synthetic form of vitamin B9. It is fully oxidised and biologically inert as supplied: dihydrofolate reductase must reduce it to tetrahydrofolate before the body can use it (StatPearls, NCBI Bookshelf NBK554487).
That is the difference from L-methylfolate (5-MTHF), which is already the circulating, reduced form — the two are different compounds with different evidence bases, and folic acid is the one that public-health policy and the prevention trials are built on.
The Institute of Medicine sets the adult RDA at 400 mcg dietary folate equivalents per day, 600 mcg DFE in pregnancy and 500 mcg DFE in lactation, and advises that anyone capable of becoming pregnant take 400 mcg of folic acid daily from fortified food, supplements, or both, in addition to food folate (NCBI Bookshelf NBK114318).
The United States has required enriched cereal-grain products to be fortified with folic acid at 140 mcg per 100 g since 1 January 1998 (FDA final rule, 61 FR 8781, 5 March 1996).
Outside the periconceptional indication, no efficacy claim is made here: the cardiovascular, stroke and cognitive literature has not been transcribed here.
Folic acid is supplied fully oxidised and is not directly usable. Dihydrofolate reductase converts it to tetrahydrofolate, the active form (StatPearls, NCBI Bookshelf NBK554487). This step is what methotrexate blocks.
Tetrahydrofolate carries one-carbon units for purine and thymidylate synthesis, which is why folate status limits rapidly dividing tissue — including the closing neural tube and the erythron.
Adequate folate around the time of conception lowers the risk of neural tube defects; the neural tube closes in the first weeks of pregnancy, which is why supplementation should start before conception, and if pregnancy has already begun it should be started promptly (USPSTF evidence review, NCBI Bookshelf NBK593617).
Actively recommended in pregnancy, rather than merely permitted. The IOM RDA in pregnancy is 600 mcg DFE/day (NCBI Bookshelf NBK114318), and the USPSTF advises 400-800 mcg of folic acid daily for anyone planning or capable of pregnancy, starting at least 1 month before conception (NCBI Bookshelf NBK593617).
The IOM RDA in lactation is 500 mcg DFE/day (NCBI Bookshelf NBK114318) and StatPearls states folic acid may be used as a supplement during breastfeeding (NBK554487).
The IOM sets lower upper limits for synthetic folic acid by age: 300 mcg/day at 1-3 years, 400 mcg/day at 4-8, 600 mcg/day at 9-13 and 800 mcg/day at 14-18 (NCBI Bookshelf NBK114318). A 400 mcg adult tablet already exceeds the limit for a child under 9.
No age-specific upper limit is set — the adult limit of 1,000 mcg/day applies (NCBI Bookshelf NBK114318). The reason to be careful is not the number: vitamin B12 deficiency is what the limit protects against, and folic acid can correct its anaemia while the neurological damage progresses (StatPearls NBK554487), so establish B12 status first.
Both interact with folate metabolism and both are prescribed alongside deliberate folate decisions. Take the dose your prescriber sets rather than adding a supplement independently.
Methotrexate works by inhibiting dihydrofolate reductase, the enzyme that converts folic acid to its active form (StatPearls, NCBI Bookshelf NBK556114). Folate supplementation alongside methotrexate is routinely prescribed for exactly this reason, but the dose and schedule are the prescriber's decision, not a self-selected one.
Deficient folate levels have been detected in up to 16% of patients taking antiepileptic drugs, including gabapentin, phenytoin, carbamazepine, valproate and primidone (StatPearls, NCBI Bookshelf NBK554487). Folate status is worth checking with the prescriber rather than self-corrected, because the interaction runs in both directions.
Folic Acid has an evidence score of 8/10 — strong evidence based on 22 indexed studies, including 1 meta-analysis. The synthetic, fully oxidised form of vitamin B9 — the compound the neural-tube-defect prevention trials and food fortification actually used. It is NOT methylfolate: it needs dihydrofolate reductase to become active. Representative study: PMID 26662928.
The commonly studied dose of Folic Acid is 400 mcg/day for anyone planning or capable of pregnancy (USPSTF: 400-800 mcg); adult RDA 400 mcg DFE/day, 600 mcg DFE in pregnancy, 500 mcg DFE in lactation (IOM). Individual needs vary — start at the lower end of the range and adjust based on how you respond.
Timing is flexible for Folic Acid — consistent daily use matters more than the time of day. Absorption is somewhat higher without food: the IOM's dietary folate equivalent factors are 0.5 mcg of a supplement taken on an empty stomach versus 0.6 mcg taken with a meal per 1 mcg DFE (NCBI Bookshelf NBK114318).
Folic Acid has a safety rating of "moderate". That is a category, not a measure of individual risk, and there are precautions worth knowing. Use caution if any of these apply to you: Untreated or undiagnosed vitamin B12 deficiency — rule B12 deficiency out before treating an apparent folate-deficiency anaemia with folic acid (StatPearls, NCBI Bookshelf NBK554487).
Vitamin B12
Likely helpsDrives nerve myelination, red blood cell formation, and DNA synthesis — deficiency is common in vegans, vegetarians, and older adults.
Vitamin D3
Probably helpsHormone-like vitamin that regulates 1,000+ genes — deficiency is widespread and linked to poor immunity, depression, and bone loss.
Prenatal Multivitamin
Too few graded studiesFolic acid has strong evidence for preventing neural tube defects when it is started before conception and continued through early pregnancy. The need for each other ingredient depends on diet, medical history and local guidance.
Vitamin B6
Too few graded studiesCofactor in 100+ enzyme reactions including serotonin, dopamine, and GABA synthesis — also lowers homocysteine levels.
Explore: Best supplements for Women's Health
Reviewed by Dr. Baher Al Hakim · Last reviewed September 2026 · evidence from 22 studies · how we score · editorial policy
This information is for educational purposes only. It is not a substitute for professional medical advice. Always consult a qualified healthcare provider before starting, stopping, or changing any supplement or medication.