Compound or practice · Supplement
Folate (B9)
Prevents neural-tube defects — the one supplement with an unambiguous public-health mandate before and in early pregnancy.
- Overall grade
- Grade A
- Last revised
- 3
- graded outcomes
- 0
- references listed
A structured monograph in Prometheus's bundled library. Its grades are the monograph's own reading of the evidence, not a peer-reviewed review.
2 at grade A · 1 at grade D — 3 graded rows
What is known
Each outcome with its grade (how strong the evidence is, A to D), the size of the effect where the entry records one, and how often studies agree.
- Neural-tube defect preventionEvidence grade A
Periconceptional; population + RCT
Largehigh
- Homocysteine loweringEvidence grade A
Reliable biomarker effect
Moderatehigh
- Cardiovascular eventsEvidence grade D
Homocysteine lowering did not cut events
Trivialhigh
What is uncertain
Read off the same rows as above. Nothing here is added that the entry does not itself record.
- Thin evidence: Cardiovascular events (grade D).
- Caution with Vitamin B12: Folate can mask B12-deficiency anemia; assess B12 alongside.
- Watch with Vitamin B12: Folate can mask B12-deficiency anemia; assess B12 alongside.
Interactions
Documented pairings with supplements and medicines. A medicine on this list is a conversation for whoever prescribes it.
Vitamin B12Caution
Folate can mask B12-deficiency anemia; assess B12 alongside.
The evidence in words
What it is
Folate is the B-vitamin required for DNA synthesis and one-carbon metabolism. 'Folate' is the natural food form; 'folic acid' is the synthetic form used in fortification and most supplements. It is most consequential in the weeks around conception and early pregnancy.
How it works
Folate carries one-carbon units for the synthesis of purines, thymidine, and methionine, making it essential for rapidly dividing cells — including the neural tube that closes in the first month of gestation. It works in tight partnership with B12 in the methylation cycle.
What the evidence shows
Grade A, and rare among supplements in having randomized-trial-and-population evidence that periconceptional folic acid substantially reduces neural-tube defects — the basis for mandatory flour fortification in many countries. Beyond pregnancy, folate lowers homocysteine reliably, but lowering homocysteine has not translated into fewer cardiovascular events in trials. Claims beyond deficiency and pregnancy are weak.
How to use it
400 µg/day for anyone who could become pregnant, started before conception; higher doses are used under medical guidance for prior affected pregnancies. General supplementation of 400 µg is reasonable where diets are low in leafy greens and legumes.
Safety & interactions
Safe at typical doses. The main caution is masking B12 deficiency (see B12). Very high folic-acid intakes and unmetabolized folic acid are debated but not clearly harmful at supplemental doses. Vitamin B12 — Folate can mask B12-deficiency anemia; assess B12 alongside.
Bottom line
If pregnancy is possible, 400 µg folic acid daily, starting before conception, is one of the best-evidenced supplements in existence. Outside that context it mainly corrects a dietary gap.
How it is used
As the entry records it, from the studies it summarises. Not a recommendation for you — doses that suit a trial population may not suit you.
- Periconceptional
- 400 µg folic acid daily, before and through early pregnancy.
- General
- 400 µg/day if leafy-green and legume intake is low.
Related reading
Entries that share this one's tags or conditions.
- Folate (B9) for Cardiovascular eventsEvidence grade D — Homocysteine lowering did not cut eventsEvidence grade D
- Folate (B9) for Homocysteine loweringEvidence grade A — Reliable biomarker effectEvidence grade A
- Folate (B9) for Neural-tube defect preventionEvidence grade A — Periconceptional; population + RCTEvidence grade A
- Folate (B9): dosage and how to take it400 µg folic acid daily, before and through early pregnancy.Evidence grade A
Sources
This entry lists no references of its own.
Last revised . A grade is this entry's reading of the evidence, not medical advice.