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Folic Acid (Vitamin B9)

Periconceptional folic acid is one of the few supplements with an unambiguous, large, replicated benefit: it prevents neural tube defects. Beyond pregnancy, it lowers homocysteine but delivers little to no cardiovascular benefit in folate-fortified populations.

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What the science says

  • Prevents neural tube defects Strong evidence

    A Cochrane review of five trials in over 6,100 women found periconceptional folic acid reduced neural tube defects by about 70% (RR ~0.31), including a 68% reduction in recurrence for women with a previously affected pregnancy. The effect is large, consistent, and is the basis for mandatory grain fortification in over 80 countries.

  • Reduces stroke risk in folate-unfortified populations Moderate evidence

    The CSPPT trial randomised 20,702 Chinese hypertensive adults in an unfortified setting to enalapril plus 0.8 mg folic acid versus enalapril alone and found a 21% reduction in first stroke over 4.5 years (2.7% vs 3.4%). Trials in fortified populations such as the US have generally been null, so the benefit appears confined to genuinely low-folate populations.

  • Prevents heart attacks or cardiovascular death Limited evidence

    Folic acid reliably lowers homocysteine by roughly 25%, but large meta-analyses of homocysteine-lowering trials show no reduction in myocardial infarction or cardiovascular mortality. This is a textbook case of a surrogate marker moving while hard outcomes do not.

  • Improves mood or cognition in the general population Limited evidence

    Trials of folic acid for depression prevention or cognitive decline in unselected adults have been largely negative. Any signal is confined to people with low folate status or those on antifolate drugs.

Dosage & safety

Studied doseRDA is 400 mcg DFE/day for adults. All women who could become pregnant should take 400-800 mcg/day of folic acid starting at least one month before conception and through the first trimester. Women with a previous NTD-affected pregnancy, or on antiepileptics, are usually advised 4-5 mg/day. CSPPT used 0.8 mg/day. Tolerable upper limit from supplements and fortified foods is 1,000 mcg/day of folic acid (the limit does not apply to food folate).
SafetyWell tolerated at standard doses. The key hazard is masking vitamin B12 deficiency: folic acid can correct the megaloblastic anaemia while the neurological damage of B12 deficiency progresses undetected — check B12 in older adults and anyone on metformin or a proton pump inhibitor before high-dose folate. Folic acid reduces the efficacy of methotrexate as a chemotherapy agent (though it is deliberately co-prescribed in rheumatology) and interacts with phenytoin, phenobarbital and pyrimethamine. Unmetabolised folic acid appears in serum at intakes above ~800 mcg/day; observational links to cancer promotion remain unproven but argue against megadosing. People with the MTHFR C677T variant still convert folic acid adequately in most cases — see L-methylfolate for the nuance.

How to take it

TimingTiming does not matter — consistency does.
With food?With or without food.
Worth knowingStart at least a month before trying to conceive: the neural tube closes by week four, often before a pregnancy test turns positive.

Interactions

With medications

  • methotrexate used as chemotherapy

    Folate directly opposes the drug's antitumour mechanism (though it is deliberately co-prescribed at low dose in rheumatology to reduce side effects). never add folate during cancer treatment without your oncologist's instruction

  • phenytoin, phenobarbital and carbamazepine

    These drugs lower folate, and folate supplementation can in turn lower drug levels and seizure control. women on antiepileptics planning pregnancy need 4-5 mg/day with neurology supervision and drug level monitoring

  • sulfasalazine

    Impairs folate absorption in the gut. routine folate supplementation is usually recommended alongside it

  • pyrimethamine and trimethoprim

    These are antifolate drugs; folic acid can reduce their antimicrobial effect. use folinic acid instead if rescue is needed, on medical advice

With other supplements

  • vitamin B12

    Folate corrects the anaemia of B12 deficiency while the neurological damage continues undetected. check B12 before taking high-dose folate, especially over 50 or on metformin or a PPI

Well-established interactions only — this is not a complete list. Always tell your doctor and pharmacist what you take.

Frequently asked questions

Why should you take folic acid before pregnancy?

Folic acid prevents neural tube defects — the evidence is strong, with a Cochrane review finding periconceptional folic acid cut them by about 70%. Start at least a month before conception, because the neural tube closes by week four.

How much folic acid per day when trying to conceive?

Most women need 400–800 mcg/day of folic acid from at least one month before conception through the first trimester. After a previous affected pregnancy or on antiepileptics, 4–5 mg/day of folic acid is usually advised under medical supervision.

Does folic acid prevent heart attacks?

No — the evidence is limited. Folic acid lowers homocysteine by roughly 25%, but large meta-analyses show no reduction in heart attacks or cardiovascular death; a stroke benefit appeared only in an unfortified population.

Can folic acid hide a B12 deficiency?

Yes. Folic acid can correct the anaemia of B12 deficiency while nerve damage continues unnoticed, so check B12 before high-dose folic acid, especially if you are older or take metformin or a PPI.

Scientific references

Where to buy

Vitamatic, Folic Acid, 400 mcg, 500 Tablets

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