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The following HTML text is provided to enhance online readability. Many aspects of typography translate only awkwardly to HTML. Please use the page image as the authoritative form to ensure accuracy. folate, but ancillary data on plasma homocysteine and plasma folate concentrations were also considered. Vitamin B12 functions as a coenzyme in the metabolism of fatty acids of odd-chain length and in methyl transfer. To estimate the requirement, the primary focus was on the amount of B12 needed for the maintenance of hematological status and serum B12 values. Pantothenic acid functions as a component of coenzyme A and phosphopantetheine, which are involved in fatty acid metabolism. The AI is based on data on pantothenic acid intake sufficient to replace urinary excretion. Biotin functions as a coenzyme in bicarbonate-dependent carboxylations. The AI is based on limited intake data. Choline functions as a precursor for acetylcholine, phospholipids, and the methyl donor betaine. The AI is based on the intake required to maintain liver function as assessed by measuring serum alanine aminotransferase levels. Although AIs have been set for choline, there are few data to assess whether a dietary supply of choline is needed at all stages of the life cycle, and it may be that the choline requirement can be met by endogenous synthesis at some of these stages. Consideration of the Risk of Developmental Abnormalities and Chronic Degenerative DiseaseClose attention was given to evidence relating intake of B vitamins and choline to reduction of the risk of developmental disability and chronic disease. Conclusions on four of these relationships follow. Neural Tube DefectsBecause pregnancy affected by a neural tube defect (NTD) occurs in only a very small fraction of the population of women in their childbearing years, reduction of the risk of NTDs is not considered compatible with the setting of the RDA for folate. That is, by definition, the EAR would need to prevent fetal NTD in 50 percent of all women in the age group and the RDA would need to prevent it in 97 to 98 percent of the women, but NTD occurrence is already much lower than this—less than 1 percent of all pregnancies. The RDA for folate recommended in this report for women ages 19 through 50 years (400 µg/day of dietary folate equivalents) is consistent with some recommendations for the prevention of NTDs. However, the amount and form of folate demonstrated in currently available studies to minimize NTD risk is 400 µg/day of folic acid in
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