The RDA for folate is set by assuming a coefficient of variation (CV) of 10 percent (see Chapter 1) because information is not available on the standard deviation of the requirement for folate; the RDA is defined as equal to the EAR plus twice the CV to cover the needs of 97 to 98 percent of the individuals in the group (therefore, for folate the RDA is 120 percent of the EAR).

Intakes higher than the RDA may be needed by women who are pregnant with more than one fetus, mothers nursing more than one infant, individuals with chronic heavy intake of alcohol, and individuals on chronic anticonvulsant or methotrexate therapy. Folate from supplements or fortified foods in addition to dietary folate is recommended for women capable of becoming pregnant.

Neural tube defects (NTDs) constitute an important public health problem in terms of mortality, morbidity, social cost, and human suffering. Many studies have been conducted regarding the association between folate intake and the occurrence of NTDs. The aim of this section is to review the evidence linking folate with the etiology and occurrence of NTDs in humans, estimate the risk of NTDs according to various levels of folate intake in the U.S. and Canadian populations, and develop a folate recommendation for women capable of becoming pregnant. Survey data indicate that fewer than half of U.S. females aged 15 to 44 years are at any appreciable risk of conceiving (Abma et al., 1997). Approximately 22 percent of them are permanently sterile (most often as a result of a specific