Folate (Vitamin B9)

What it does

Folate is the family name for vitamin B9. Food folate and the synthetic form folic acid must be converted, ultimately to 5-methyltetrahydrofolate (5-MTHF), to drive one-carbon metabolism: DNA synthesis and repair, red blood cell formation, and the conversion of homocysteine to methionine. L-methylfolate supplements supply 5-MTHF directly, bypassing the DHFR and MTHFR steps. The distinctions that matter are life stage (the neural tube closes by day 28 of pregnancy), baseline status, and which outcome you ask about: blood markers move easily, clinical events mostly have not.

What the research says

• Prevents neural tube defects (spina bifida, anencephaly) when taken before conception and in early pregnancy

  Evidence: strong. The MRC Vitamin Study (Lancet 1991), a randomized trial in 1,817 women at high risk of an NTD-affected pregnancy, found folic acid 4 mg/day cut recurrence by 72 percent (RR 0.28). The Hungarian trial of a folic-acid-containing multivitamin showed prevention of first occurrences, and mandatory fortification was followed by large population declines in NTDs. This is the strongest single supplement-prevention result in nutrition, and it is time-locked: the neural tube closes in the first 28 days, often before a pregnancy is recognized, which is why the recommendation targets everyone who could become pregnant.

• Lowers homocysteine, with a stroke reduction signal concentrated in low-folate, unfortified populations

  Evidence: moderate. Folic acid reliably lowers homocysteine about 20 to 25 percent. Events are another matter. CSPPT (Huo et al., JAMA 2015) randomized 20,702 Chinese hypertensive adults without folate fortification to enalapril plus folic acid 0.8 mg versus enalapril alone: first stroke fell from 3.4 to 2.7 percent (HR 0.79) over 4.5 years. In fortified or folate-replete settings the signal largely disappears: HOPE-2 (N Engl J Med 2006, n = 5,522) found no effect on the cardiovascular composite (RR 0.95) with a nominally lower stroke outcome (RR 0.75), and NORVIT raised early harm concerns after myocardial infarction. Read: a real effect where deficiency is common, not a general cardiovascular intervention.

• Improves cognition or prevents dementia in older adults

  Evidence: weak. FACIT (Durga et al., Lancet 2007) randomized 818 older adults with elevated homocysteine to folic acid 800 mcg/day for 3 years and found better memory and information-processing speed versus placebo, the best positive cognition result for folate alone. It has not been matched by event-level evidence: larger B-vitamin trials with folic acid plus B12 (B-PROOF) were null for cognitive decline, and no trial shows folate prevents dementia. A single positive trial on test scores in a high-homocysteine Dutch population is a hypothesis, not a recommendation engine.

Folate holds one of the few A-grade results in all of supplementation: periconceptional folic acid prevents neural tube defects, proven in randomized trials (MRC 1991, 72 percent reduction in recurrence) and confirmed at population scale by fortification. That result alone keeps folate out of the C band. The grade stops at B- because the benefit is confined to a narrow window and population, while the broader longevity pitch has repeatedly failed: homocysteine lowering is real, but HOPE-2 and NORVIT found no cardiovascular event benefit in folate-replete populations, the CSPPT stroke result comes from an unfortified, low-folate setting and may be a deficiency-correction effect, and cognition rests on one positive trial (FACIT) against null larger trials. Add two genuine cautions (masking of B12 deficiency, and unresolved questions about high folic acid intake and unmetabolized folic acid) and the honest summary is: essential for women who could become pregnant, reasonable insurance at RDA doses for others, unproven as a longevity or brain intervention.

What the experts say

Every position links to its source. We include skeptics alongside supporters.

• Bryan Johnson

  Source, 2026-09-10 Takes 200 mcg DFE/day of folate as calcium L-5-methyltetrahydrofolate in his Blueprint Essential Capsules, in the morning with food, per the published Blueprint protocol (compiled in our expert-stacks.json; the form detail comes from secondary listings reproducing the product label). Half the adult RDA from the pill: a top-up dose consistent with the insurance framing, not an intervention dose.

• Peter Attia

  Takes methylfolate (the 5-MTHF form) rather than folic acid: his own transcript confirms he takes methyl folate because of an MTHFR variant and to manage homocysteine. A secondary stack summary lists Jarrow methylfolate at 400 mcg/day; that dose is secondary-sourced, not primary-verified. Note the graded context: HOPE-2 and NORVIT found no cardiovascular event benefit from homocysteine lowering, so this is a practice preference, not an outcome-backed strategy.

Is it worth it?

Derived under the October 2026 worth-it model: B- evidence (2.7 points) at $3 to $8 a month scores 2.64, which bands to B+. The decisive use is preventing neural tube defects for anyone who could become pregnant, among the best-value purchases in the database; for everyone else it is an RDA-dose nutrient most diets and fortified foods already cover, and the B- evidence grade is what sets the score. An earlier stored grade of B was an editorial override and has been corrected to the derivation.

Frequently asked questions