Folate (folic acid)

What it is

Folate is the natural B9 vitamin found in leafy greens, legumes, asparagus, citrus fruit and fortified cereals. Folic acid is the synthetic form used in supplements and food fortification. Methylfolate (5-MTHF) is the active form your body uses.

Its best-known use is in pregnancy: UK advice is that anyone trying to conceive should take folic acid daily until the 12th week of pregnancy, because it lowers the chance of neural tube defects such as spina bifida.

Adults not planning pregnancy mostly get enough from food, though some medicines and conditions raise needs.

How it works

Folate is needed to make DNA and red blood cells and to process the amino acid homocysteine. Folic acid is converted to the active form in the liver; some people convert it more slowly because of gene variants, which is the basis of the methylfolate marketing.

What the evidence says

• Strong Reducing neural tube defect risk in early pregnancy
  One of the best-established supplement benefits; should start before conception.
• Strong Correcting folate-deficiency anaemia
  Works when low folate is the cause.
• Strong Lowering homocysteine
  It reliably lowers this blood marker, but that has not translated into clear heart attack or stroke reduction.
• Limited Mood, as an add-on in depression
  Some trials of methylfolate with antidepressants show benefit in selected people; not an alternative to treatment.
• Limited Cognition in older adults
  Mixed results, mostly in combination with B12.

Evidence ratings are our plain-English summary of how much good human research exists, not a promise of results. How we rate evidence.

Dosage and timing

• UK advice for people trying to conceive: 400 micrograms (0.4 mg) of folic acid daily from before conception until week 12 of pregnancy.
• A higher dose of 5 mg is prescribed for some groups (for example a past neural tube pregnancy, diabetes, epilepsy medicines, obesity); this is on prescription, so speak to your GP or midwife.
• For general health, the adult reference intake is about 200 micrograms from diet; check current guidance.
• The UK is moving towards fortifying flour with folic acid, so check current advice.

Forms and what to look for

• Folic acid is the studied form for pregnancy and is cheap.
• L-methylfolate (5-MTHF) is marketed for people with MTHFR variants; for pregnancy, the evidence base is for folic acid, so ask your midwife or doctor before swapping.
• Folinic acid (leucovorin) is a prescription medicine used for specific purposes.
• Prenatal multivitamins contain folic acid, often with vitamin D.

What to expect, and when

• For pregnancy, take it at least a month before conception ideally, and keep going until week 12.
• Anaemia from deficiency usually improves over weeks.
• You will not feel anything in normal circumstances.

Side effects

• Usually very well tolerated at normal doses.
• Nausea, bloating or loss of appetite occasionally.
• Sleep disturbance or vivid dreams in some.
• High-dose methylfolate can cause irritability, anxiety or agitation in some people.

Interactions

• Methotrexate works by blocking folate pathways; do not add folic acid unless your specialist directs it.
• Phenytoin and other anti-seizure medicines can have levels altered.
• Sulfasalazine and trimethoprim can reduce folate.
• Folic acid can hide B12 deficiency, so levels of both matter.

Who should avoid it

• Anyone on methotrexate or anti-seizure medicines without medical advice.
• People with untreated B12 deficiency.
• People with a history of certain cancers should speak to a clinician before taking high doses.
• Do not self-start 5 mg doses; they need a prescription.

Risks and safety

• Doses above 1 mg a day of folic acid may mask B12 deficiency (UK advisory upper limit for supplements is generally 1 mg a day; check current guidance).
• Not banned in sport.
• Unmetabolised folic acid in blood is debated; the long-term significance is unclear.
• Products labelled with "DFE" (dietary folate equivalents) can confuse dose comparisons.

Buying well: quality and testing

• Check whether the label uses micrograms of folic acid or DFE.
• For pregnancy, choose a product designed for it, or plain 400 microgram folic acid.
• Third-party seals (NSF, USP) add confidence.
• Be wary of extreme-dose methylfolate products.

Bottom line

Folic acid before and in early pregnancy is among the strongest supplement recommendations there is, and it is cheap. Outside pregnancy or deficiency, the benefits are smaller; speak to your GP or midwife about your personal dose.