Folate, a B vitamin in leafy greens, beans and fortified grain. Folic acid is the usual supplement form. Most studied for preventing birth defects of the spine and brain.
Ask a doctor or pharmacist before taking folic acid if you:
Vitamin B9 is folate, a B vitamin that the body needs to make DNA and for cells to divide.[1] Food contains natural folates. Fortified foods and most supplements contain folic acid, and some supplements contain 5-MTHF, also called L-methylfolate.[1] Spinach, liver, asparagus and Brussels sprouts are among the richest foods.[1]
Mainly to prevent neural tube defects, birth defects of the spine and brain: in a Cochrane review, folic acid around conception lowered their risk by 69% (risk ratio 0.31).[4] A review of 21 trials found 10% fewer strokes, mainly where grain is not fortified.[5] B vitamins did not prevent heart attacks.[6] Most trials found no effect on memory.[1]
Folate from food has not been reported to cause harm.[1] For folic acid from supplements and fortified foods, the US and the EU set an upper limit of 1,000 µg a day for adults.[1][7] Large doses can hide a vitamin B12 deficiency, and folate interacts with methotrexate and some medicines for epilepsy.[1]
Vitamin B9, or folate, helps the body make DNA and turn the amino acid homocysteine into methionine. Food contains natural folates, and most supplements contain folic acid.[1]
In the gut, food folates are cut into a simpler form and taken up by the gut wall. The body absorbs about 85% of folic acid taken with food, but only about 50% of the folate in food.[1]
Before folate enters the blood, an enzyme called dihydrofolate reductase changes it into active forms. The main form in blood is 5-MTHF. When a dose is larger than this enzyme can handle, unchanged folic acid appears in the blood.[1]
Folate is needed to make one of the building blocks of DNA. Without enough folate, cells cannot divide normally, and this can lead to megaloblastic anemia, with large, abnormal red blood cells.[1]
The body needs 5-MTHF to turn homocysteine into methionine. When there is not enough 5-MTHF, this step slows and homocysteine in the blood rises.[1]
The body holds 15 to 30 mg of folate. About half of it is in the liver, and the rest is in the blood and other tissues.[1]
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The trials that prevented neural tube defects gave 400 µg (0.4 mg) of folic acid a day or more.[4] The daily need of adults is 400 µg DFE in the US and 330 µg DFE in the EU.[1][8]
Before and in early pregnancy, the US Preventive Services Task Force recommends 400 to 800 µg of folic acid a day, and WHO 400 µg a day.[9][3] After a pregnancy with a neural tube defect, WHO says women should be offered 5 mg a day.[3] A large stroke trial gave 0.8 mg a day with a blood pressure medicine.[10] For lowering homocysteine, 0.5 to 5 mg a day had a similar effect.[11]
In the US, the recommended amount (RDA) is 400 µg DFE a day for everyone from 14 years, 600 µg DFE in pregnancy and 500 µg DFE while breastfeeding. Children aged 1 to 13 need 150 to 300 µg DFE, depending on age.[1] EFSA sets 330 µg DFE a day for adults, 600 µg DFE in pregnancy and 500 µg DFE while breastfeeding.[8]
In the US, the upper limit for folic acid from supplements and fortified foods is 1,000 µg a day for adults, also in pregnancy. For children it is 300 to 800 µg, depending on age. There is no limit for folate from food.[1] EFSA keeps the same 1,000 µg a day for adults, and the limit includes the 5-MTHF forms.[7] Higher doses are taken only under medical care.[1]
Most studies gave 0.25 to 0.5 mg a day, for 1 to 3 months.
The counts are study groups. A study group is one set of people in a study who took the same dose. One study can have several groups. These are amounts from studies, not advice for you.
35 of 101 study groups took vitamin B9 with something else. This shows what studies gave together, not what works together.
What studies used when they gave vitamin B9 for one goal, or to a group of people.
Each protocol describes what studies used, for one goal or for one group of people. It is not advice for you: talk to a doctor before you start a supplement.
12 questions in 4 groups. Open one for the short answer; each has its own page with the full answer and sources.
Beef liver has 215 µg DFE in 3 ounces, boiled spinach 131 µg in half a cup, and black-eyed peas 105 µg in half a cup.[1] Asparagus, Brussels sprouts, avocado and broccoli are good sources too. In the US, folic acid must be added to enriched bread, flour, pasta and rice, and in Canada to enriched flour, pasta and corn meal.[1]
A clear folate deficiency is rare in the US.[1] The groups most at risk are people with alcohol use disorder, women who could become pregnant, and pregnant women. People with celiac disease, inflammatory bowel disease or other conditions that lower absorption are also at risk. About 20% to 60% of people with inflammatory bowel disease are low in folate.[1]
Weeks to months. In a 24-week trial in 144 young women, folate in plasma, the liquid part of the blood, stopped rising after 12 weeks. Folate in red blood cells was still rising at 24 weeks.[12] A calculation from two trials in young women puts the time to a stable red blood cell level at about 40 weeks.[13] The authors suggest starting more than 4 weeks before pregnancy.[12]
Yes, for neural tube defects such as spina bifida. A 2015 Cochrane review of 5 trials found that folic acid around conception lowered their risk by 69% (risk ratio 0.31), with high-quality evidence.[4] It had no clear effect on other birth defects.[4] The US Preventive Services Task Force recommends 400 to 800 µg a day for everyone who could become pregnant.[9]
A little, mainly where grain is not fortified with folic acid. A 2024 review of 21 trials with 115,559 people found 10% fewer strokes (risk ratio 0.90). In areas without fortified grain or with only partly fortified grain the risk ratio was 0.83, and in areas with fortified grain 1.04.[5] In a trial of 20,702 Chinese adults with high blood pressure, 0.8 mg of folic acid with a blood pressure medicine lowered first strokes from 3.4% to 2.7% over 4.5 years.[10] B vitamins that lower homocysteine did not prevent heart attacks.[6]
Probably not for most people. Most trials found no effect on memory or dementia, even when folic acid lowered homocysteine.[1] In a Dutch trial of 818 people aged 50 to 70 with high homocysteine, 800 µg a day for 3 years: memory changed for the better compared with placebo.[14] A 2022 review found that B vitamins changed a memory and thinking test score by only 0.14 points.[15]
There is no evidence for folate on its own: no trial in a 2018 review compared folate alone with placebo. Added to an antidepressant, folic acid below 5 mg a day or L-methylfolate at 15 mg a day showed a benefit, with low-quality evidence.[16] In a UK trial of 475 adults, 5,000 µg of folic acid added to antidepressants did not help. Doses this high are taken only under medical care.[1]
The evidence is about anemia, not about energy in healthy people. A lack of folate causes megaloblastic anemia, with weakness, tiredness and shortness of breath.[1] In 371 pregnant women with iron deficiency anemia, iron with folinic acid, a form of folate, raised hemoglobin more than iron alone. The trial measured hemoglobin, not tiredness.[17]
Trials found no clear effect overall. A 2013 analysis of 13 trials with 49,621 people found no change in cancer over about 5 years (rate ratio 1.06).[18] Some single trials found more cancers, including prostate cancer, and the effect in people who have had colorectal polyps or cancer is unclear.[1]
For rheumatoid arthritis, trials gave folic acid with low-dose methotrexate. A 2013 Cochrane review of 6 trials with 624 patients found 26% fewer stomach and gut side effects and 77% fewer abnormal liver tests, and methotrexate worked as well.[2] For cancer treatment it is different: folate could interfere with the drug, so the oncologist should be asked first.[1]
Folate is the name for all forms of vitamin B9. Folic acid is the synthetic form in fortified foods and most supplements.[1] The body absorbs about 85% of folic acid taken with food and about 50% of the folate in food. This is why labels use dietary folate equivalents (DFE): 1 µg DFE is 1 µg of food folate or 0.6 µg of folic acid taken with food.[1]
Not proven. 5-MTHF (methylfolate) is absorbed as well as folic acid or better, and in one trial it raised red blood cell folate more.[1][12] But the trials that prevented neural tube defects used folic acid.[4] The US CDC recommends folic acid for everyone who could become pregnant, even with the MTHFR gene variant.[1]
