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Folic acid, also called folate or vitamin B₉, is essential for cell formation and growth, particularly of blood cells. It is found in several foods (see box above). A well-balanced diet with a variety of healthful foods should supply all the folic acid your body needs. The recommended dietary allowance (RDA) of folic acid for adults over 50 is 400 micrograms per day for both men and women.

It is unlikely that you would have a diet-related folic acid deficiency. Rather, certain medical conditions or the long-term use of several drugs can lead to a folic acid deficiency. Alcoholism is perhaps the most common cause because alcoholics often eat an inadequate diet. Some diseases of the small intestine can also interfere with your body’s absorption of folic acid, resulting in less of it available for the body to use. Long-term treatment with drugs such as methotrexate, trimethoprim, triamterene, corticosteroids, certain painkillers, sulfasalazine and some anticonvulsants (phenobarbital, phenytoin, and primidone) can also cause a folic acid deficiency.

If you have to increase your intake of folic acid in order to prevent or treat a deficiency, eat folate-rich foods rather than taking a vitamin supplement. (See table above.) You should only take a supplement when you have a clear need for more folic acid and when you cannot get enough from your diet. You should not take a supplement until your doctor has made sure that you do not have pernicious anemia, a disease resulting in vitamin B₁₂ deficiency. Folic acid supplements can hide the easily detected symptoms of pernicious anemia while allowing irreversible nervous system damage to occur undetected.

Folic acid has been shown to prevent neural tube defects, a serious type of birth defect, and, as of January 1998, all grains sold in the United States contain 140 micrograms of folic acid per 100 grams (about 3 ounces). Even this amount, however, may be inadequate for prevention of neural tube defects, which occur early in pregnancy, before most women know that they are pregnant. The current recommendation is that women of childbearing age should also receive 400 micrograms of folic acid per day.[1]

“The main concern regarding ingestion of excess folic acid is the consequential masking of vitamin B₁₂ deficiency. A general consistency of data indicates that supplementation with 1 mg/day or less of folic acid does not mask vitamin B₁₂-associated anaemia in the majority of subjects, whereas supplementation with 5 mg/day or more of folic acid does. The effects of doses of between 1 and 5 mg/day are unclear. No other significant adverse effects have been associated with ingestion of folic acid. For guidance purposes only, in the general population a supplemental dose of 1 mg/day would not be expected to cause adverse effects. Assuming a maximum intake from food of approximately 0.49 mg/day, a total dose of 1.5 mg/day would not be expected to have any adverse effects.”[2]

A recent randomized trial sought to find out if folic acid supplements (0.5 milligrams per day) would decrease the rate of death and cardiovascular events in people with stable coronary artery disease. After two years of folic acid supplements, there was no improvement in outcomes in those who got folic acid compared to those randomized to get standard care. The authors concluded that “low-dose folic acid supplementation should be treated with reservation” and that “the study does not seem to support the routine use of folic acid in patients with stable CAD [coronary artery disease].”[3]

In addition, two studies posted on the web site of the New England Journal of Medicine on March 12, 2006, showed that vitamin supplementation with folic acid, vitamin B₆, and vitamin B₁₂ did not reduce the risk of major cardiovascular outcomes, such as heart attack or stroke, in patients with preexisting cardiovascular disease or after a heart attack.[4],[5]

A recent Journal of Parenteral and Enteral Nutrition (JPEN) systematic review revealed that, with a few possible exceptions, dietary supplements offer no benefits to well-nourished adults eating a Western diet and, in many cases, may be harmful. The results of this study reinforce Worst Pills, Best Pills News’s longstanding view that there is little evidence that dietary supplements are either safe or effective.

The study authors concluded that, with the possible exception of vitamin D in elderly patients and omega-3 fatty acids in patients with a history of cardiovascular disease, no data support the widespread use of dietary supplements in the U.S. and other Western countries. Indeed, the data suggest that certain commonly used dietary supplements, including beta-carotene, vitamin A and vitamin E, may be harmful. We agree.[6]

If you take folic acid without a doctor’s supervision, do not exceed the RDA.

The following information does not apply to the vitamin B₁₂ component. See the vitamin B12 [cyanocobalamin] profile for more information.

In 2023, Movement Disorders published an article which showed that taking Vitamin B₆ (pyridoxine), B₉ (folate) and B₁₂ (cobalamin) supplements for a long time and taking more than the daily recommended dose did not decrease the risk of Parkinson’s disease.[7]