Folate (vitamin B9) is a B vitamin the body needs to make DNA and divide cells. Folic acid is the form in most supplements and fortified foods; some supplements use 5-MTHF (methylfolate). It is used to prevent deficiency and, before and during early pregnancy, to lower the risk of neural tube defects.
Also known as: folic acid, methylfolate, 5-MTHF, vitamin B9.
ODS lists a Recommended Dietary Allowance of 400 mcg DFE (dietary folate equivalents) a day for adults, 600 mcg DFE in pregnancy and 500 mcg DFE while breastfeeding. The Tolerable Upper Intake Level for adults is 1,000 mcg a day of folic acid from supplements and fortified foods (not from food folate). Adult supplements commonly contain 400 to 800 mcg of folic acid (680 to 1,360 mcg DFE).
It is sold in the US as a dietary supplement. Under the 1994 dietary supplement law (DSHEA), FDA does not approve dietary supplements before they are marketed, and the maker, not FDA, is responsible for safety and labeling.
ODS explains the units: 1 mcg DFE equals 1 mcg of food folate, 0.6 mcg of folic acid taken with food, or 0.5 mcg on an empty stomach. Conversion factors for 5-MTHF have not been formally set. People with the MTHFR 677C>T variant convert folate to 5-MTHF less well; ODS says research on supplements for them is inconclusive and that the CDC still recommends 400 mcg a day of folic acid for anyone who could become pregnant.
The main caution: large amounts of folate can correct the anemia of vitamin B12 deficiency but not its nerve damage, so they can hide or worsen low B12. Methotrexate is a folate antagonist (people taking it for cancer should ask their oncologist first), antiepileptic drugs such as phenytoin, carbamazepine and valproate lower folate and folate may lower their levels, and sulfasalazine reduces folate absorption (ODS).
We could not find a single published half-life or time to peak for folate that applies to a supplement dose, so we do not list one. ODS notes that single doses of 300 to 400 mcg of folic acid leave detectable unmetabolized folic acid in blood, while 100 to 200 mcg do not.
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