Folate

How much you need

The official Recommended Dietary Allowance for adults, per day:

Amounts are in dietary folate equivalents (DFE), which allow for folic acid being better absorbed than the folate in food — 1 mcg DFE is 1 mcg of food folate, 0.6 mcg of folic acid from fortified foods or from supplements taken with food, or 0.5 mcg of folic acid from a supplement taken on an empty stomach. Separately, the Food and Nutrition Board advises everyone who could become pregnant to get 400 mcg of folic acid a day from supplements, fortified foods or both, on top of the folate in a varied diet.

People aged 18 fall in the official 14–18 group, which has the same values — 400 mcg DFE a day, 600 mcg DFE in pregnancy and 500 mcg DFE when breastfeeding. Its upper limit is lower, at 800 mcg of folic acid from supplements and fortified foods. Pregnancy and breastfeeding change what you need — confirm yours with your midwife, obstetrician or doctor.

Upper limit

This limit applies only to folic acid and other synthetic forms of folate from supplements and fortified foods — not to folate found naturally in food.

The limit is the most folic acid from supplements and fortified foods a day that is unlikely to cause harm, not a target. It is in plain mcg, not mcg DFE like the recommended amount — 1,000 mcg of folic acid equals 1,667 mcg DFE. It was set because of the way folate interacts with vitamin B12; no limit was set for folate from food, because high intakes from food have not been reported to cause harm. It does not apply to people taking high doses under medical supervision.

What it does

Folate, sometimes called vitamin B9, is a water-soluble B vitamin ^[1]. It works as a coenzyme in making DNA and RNA and in the metabolism of amino acids, including the conversion of homocysteine to methionine ^[1]. One folate-dependent step in making DNA is required for proper cell division; when it fails, the result can be megaloblastic anemia, a hallmark of folate deficiency ^[1]. The body holds about 15 to 30 mg of folate, about half of it in the liver ^[1].

Forms

Folate is the general term for the folates found naturally in food and the forms in supplements and fortified foods ^[1]. Folic acid is the form used in fortified foods and most supplements; some supplements contain 5-MTHF (also sold as L-methylfolate) instead ^[1]. At least 85% of folic acid is absorbed when taken with food, and nearly 100% on an empty stomach, against about 50% of the folate naturally present in food ^[1]. 5-MTHF is absorbed as well as folic acid or better, but no official factor for converting it to DFE has been set ^[1]. Common supplement amounts for adults are 680 to 1,360 mcg DFE (400 to 800 mcg folic acid) ^[1].

Where it comes from

1. Beef liver, braised3 ounces215 mcg DFE
2. Spinach, boiled½ cup131 mcg DFE
3. Black-eyed peas (cowpeas), boiled½ cup105 mcg DFE
4. Breakfast cereals, fortified with 25% of the Daily Valuefortified1 serving100 mcg DFE
5. Rice, white, medium grain, cookedfortified½ cup90 mcg DFE

How these five were chosen: The five foods with the most folate per serving in the NIH fact sheet's food table. Fortified foods are marked.

In the United States

Most Americans get enough folate: in national survey data from 2013–2014, average intake from food was 602 mcg DFE a day for men aged 20 and older and 455 mcg DFE for women ^[1]. Some groups still fall short — even counting supplements, 17% of women aged 19 to 30 and 23% of non-Hispanic black women do not meet the average requirement ^[1]. Since 1998 the FDA has required folic acid to be added to enriched breads, cereals, flours, corn meals, pastas, rice and other grain products, which raised average folic acid intake by about 190 mcg a day ^[1]. About 35% of adults take a supplement containing folic acid, and about 5% of adults aged 51 to 70 and of men 71 and older take in more than the upper limit, mainly from supplements ^[1].

Who is most likely to run low

• People with alcohol use disorder — diets are often poor, and alcohol interferes with folate absorption and speeds its breakdown and excretion ^[1]
• Women who could become pregnant — some get too little even when they take supplements ^[1]
• Pregnant women, whose recommended amount rises from 400 to 600 mcg DFE, which can be hard to reach through diet alone ^[1]
• People with malabsorptive disorders such as tropical sprue, celiac disease and inflammatory bowel disease, or with reduced stomach acid ^[1]
• People with the 677C>T variant of the MTHFR gene, who convert folate to its active form less efficiently — about 25% of Hispanics, 10% of Caucasians and Asians, and 1% of African Americans carry two copies ^[1]

What deficiency looks like

Isolated folate deficiency is uncommon; it usually comes with other deficiencies, because it is closely linked with poor diet, alcohol use disorder and malabsorption ^[1]. Its main sign is megaloblastic anemia, with weakness, fatigue, difficulty concentrating, irritability, headache, heart palpitations and shortness of breath ^[1]. It can also cause soreness and shallow ulcers on the tongue and inside the mouth; changes in skin, hair or fingernail colour; digestive symptoms; and raised blood homocysteine ^[1]. Women with too little folate are at greater risk of having a baby with a neural tube defect ^[1]. A serum folate above 3 ng/mL, or a red blood cell folate above 140 ng/mL, indicates adequate status ^[1].

What the evidence supports, and what it doesn't

Established. Neural tube defects. Trial evidence shows that enough folic acid around conception prevents a substantial share of neural tube defects, and since mandatory fortification began in 1998, U.S. rates have fallen by 28% ^[1]. Folate is also essential for making DNA, which is why the recommended amount rises in pregnancy ^[1].

Not supported by trials. Heart disease: folic acid lowers homocysteine but does not reduce the risk of heart attacks or other cardiovascular outcomes apart from stroke — in one trial, 5,442 U.S. women aged 42 or older at high risk of cardiovascular disease who took 2,500 mcg folic acid with vitamins B12 and B6 a day for 7.3 years had no fewer major cardiovascular events ^[1]. Cognition: most trials find no effect on cognitive function or dementia even as homocysteine falls; a meta-analysis of 11 trials in more than 20,000 older adults found no effect on cognitive ageing ^[1]. Cancer prevention: a 2015 expert panel convened by the National Toxicology Program and the NIH Office of Dietary Supplements concluded that folic acid supplements do not reduce cancer risk in people whose folate status is already adequate ^[1].

Mixed. Stroke: folic acid, alone or with other B vitamins, reduces stroke risk, especially where folate status is low. In a trial in 20,702 adults with high blood pressure in regions of China without fortification, 800 mcg a day with the blood pressure drug enalapril for a median of 4.5 years cut strokes by 21% compared with enalapril alone; the fact sheet suggests the benefit is mainly for people with too little folate, which is less common in fortified countries such as the United States ^[1]. Cancer risk at high doses: some trials have found more cancers with folic acid — a meta-analysis of six trials in 25,738 men found 24% more prostate cancer — and the fact sheet calls its effect on cancer unclear ^[1]. Autism: observational studies suggest a possible link between folic acid around conception and lower risk, but confounding prevents firm conclusions ^[1]. Depression: results are mixed, and many doses studied exceed the upper limit and should be taken only under medical supervision ^[1].

Where official guidance disagrees

For anyone who could become pregnant, the Food and Nutrition Board advises 400 mcg of folic acid a day from supplements, fortified foods or both ^[1]. The U.S. Preventive Services Task Force recommends a daily supplement of 400 to 800 mcg folic acid, starting at least 1 month before conception and continuing through the first 2 to 3 months of pregnancy ^[1]. The CDC recommends folic acid rather than 5-MTHF, even for people with the MTHFR variant ^[1]. The Food and Nutrition Board has made no recommendation for women who have had a pregnancy affected by a neural tube defect; other experts recommend 4,000 to 5,000 mcg a day, which exceeds the upper limit and should be taken only under medical supervision ^[1].

Too much

Large amounts of folate can correct the anemia caused by vitamin B12 deficiency but not its nerve damage, so high intakes from supplements might hide a B12 deficiency until the damage is irreversible; concern has since shifted to the possibility that large amounts worsen the anemia and cognitive symptoms of B12 deficiency ^[1]. High folic acid intakes might speed the progression of precancerous lesions, raising the risk of colorectal and possibly other cancers in some people ^[1]. Intakes of 1,000 mcg or more a day from supplements around conception have been linked to lower scores on tests of cognitive development in children at age 4 to 5 ^[1]. Folic acid beyond what the body can process circulates unmetabolised; single doses of 300 or 400 mcg produce detectable levels, and what that means for health is not well understood ^[1]. Folate from food has not been reported to cause harm ^[1].

Medicines that interact

Methotrexate, used to treat cancer and autoimmune diseases, works against folate: people taking it for cancer should consult their oncologist before taking folate supplements, although supplements might reduce the digestive side effects of low-dose methotrexate for rheumatoid arthritis or psoriasis ^[1]. Antiepileptic drugs such as phenytoin (Dilantin), carbamazepine and valproate can lower blood folate, and folate supplements might lower blood levels of these drugs ^[1]. Sulfasalazine (Azulfidine), used mainly for ulcerative colitis, blocks folate absorption and can cause deficiency ^[1]. If you take any of these regularly, talk to your doctor or pharmacist before taking a folate supplement.