Folate and bioavailability
Recommended Dietary Allowances (RDA) for folate
Other key folate recommendations

Folate and bioavailability

Folate is a water-soluble B vitamin that functions as a coenzyme and participants in a variety of single-carbon transfer reactions in the body. Folate is necessary for DNA synthesis, purine synthesis, and amino acid interconversions.

Several terms are used to describe the different forms of this vitamin.

•  The term "folic acid" is used to denote the synthetic form of the vitamin used in vitamin supplements or fortified foods.

•  The terms "food folate", "naturally occurring folate", or "folate-rich foods" are used to denote the form of the vitamin found naturally in certain foods.

•  Many times, the generic term "folate" is used to describe both forms of the vitamin.  

Folic acid, the synthetic form of the vitamin, is more readily absorbed by the body compared to food folate, the natural form of the vitamin found in certain foods.

The body absorbs folic acid more readily than it does food folate. It is estimated that 50% of ingested food folate is absorbed. In contrast, approximately 85% of folic acid when consumed with food and 100% of folic acid when consumed as a supplement on an empty stomach is absorbed. Therefore, folic acid in food is 1.7 times (85 divided by 50) more bioavailable than food folate. A folic acid supplement taken on an empty stomach is 2 times (100 divided by 50) as bioavailable as food folate.

The Dietary Folate Equivalent (DFE), used to express the Recommended Dietary Allowances (RDA) for folate (see next section), takes into account the difference in bioavailability between folic acid and food folate. Despite the differences in absorption, once in the bloodstream, the biological function of both forms of the vitamin is the same.   

Recommended Dietary Allowances (RDA) for folate

The Institute of Medicine has established the following Recommended Dietary Allowances (RDA) for folate:

Source: Institute of Medicine, National Academy of Sciences. Dietary Reference Intakes for Thiamin, Riboflavin, Niacin, Vitamin B6, Folate, Vitamin B12, Pantothenic Acid, Biotin, and Choline. National Academy Press, Washington DC, 1998.

*   DFE = dietary folate equivalents.
**   Adequate Intake amount.
†  Women should continue to get 400 micrograms of folic acid from supplements or fortified foods until their pregnancy is confirmed and they begin prenatal care.

Other key folate recommendations

The U.S. Public Health Service and the Institute of Medicine recommend that all women of childbearing age consume 400 micrograms of folic acid every day, from a supplement or fortified foods, in addition to consuming food folate from a varied diet. This recommendation would also apply to teenage and younger girls who have reached menses. Click here for more information about folic acid and birth defects.

The U.S. Public Health Service recommends that women who have had a previous pregnancy affected by a neural tube defect should see their doctor because they may need a higher amount of folic acid (4.0 milligrams or 4000 micrograms) if planning another pregnancy. Women should not try to get extra folic acid by taking more than one multivitamin per day as this might lead to unhealthy intake levels of other vitamins such as vitamin A.