In 1998, the National Academy of Sciences Institute of Medicine issued the following Recommended Dietary Allowances (RDA) for folate for different groups in the population.
Group Folate RDA
0-6 months 65 mcg
6-12 months 80 mcg
1-3 years 150 mcg
4-8 years 200 mcg
9-13 years 300 mcg
14+ years 400 mcg
Pregnant females 600 mcg
Lactating females 500 mcg
The RDA set by the Institute of Medicine was increased in 1998 from 180 to 400 mcg (or ug) and to 600 mcg (or ug) during pregnancy. The new values are described as “dietary folate equivalents” and are designed to account for the fact that food folate has an average of about 50% less bioavailability than synthetic folic acid. One DFE of folate is equal to 1 ug of food folate, which is also equivalent to 0.6 ug of folic acid consumed with food or 0.5 ug of synthetic folic acid taken as a supplement on an empty stomach.
The Institute of Medicine also recommends that all women of childbearing age consume 400 ug of folic acid daily from fortified food products and/or supplements in addition to eating a varied diet containing foods that are naturally rich in folate.
The Tolerable Upper Limit (UL) for folic acid set by the Institute of Medicine in 1998 is 1,000 mcg for adults 19 years and over. This level applies only to synthetic folate; the form obtained from supplements or fortified foods. There is no evidence of any risk to health of a high intake of folate occurring in food naturally.
Folate status can be measured in three ways: concentrations in the plasma, serum, or red blood cells. Serum and plasma levels are based on recent dietary intake, with a serum concentration of less than three ug/L typically suggesting deficiency. However, red blood cell (RBC) folate concentrations provide a more reliable measure of folate tissue status. RBC concentrations of less than .140 ng/mL suggest folate deficiency, although a vitamin B 12 deficiency can produce similar results. Likewise, a deficiency of either vitamin can cause elevated concentrations of homocysteine.