food sources is similar to that of selenium (J. Holden, Agricultural Research Service, U.S. Department of Agriculture, personal communication, April 13, 1999).
Infant formulas are often fortified with selenium, and selenium supplements for adults (usually inorganic selenium salts) are becoming more common. The bioavailability of selenate and selenite, the two inorganic forms of selenium commonly used for supplementation, is roughly equivalent and generally exceeds 50 percent (Thomson and Robinson, 1986). Selenium found naturally in foods is primarily in the forms of selenomethionine and selenocysteine, which are organic selenium compounds. The bioavailability of selenium in the form of selenomethionine is greater than 90 percent (Thomson and Robinson, 1986). The selenium in selenocysteine is also highly bioavailable (Swanson et al., 1991). Thus selenium supplements with yeast as the selenium source have higher bioavailability than inorganic supplements. In general, food composition tables do not distinguish these sources. Estimated intakes through self-selected diets are shown in Appendix Table C-6, and total intakes (food and supplements) according to NHANES III are shown in Appendix Table C-7.
The contribution of water to selenium intakes is generally trivial in comparison to food selenium (NRC, 1980) and does not have to be added to intake assessments, unless water from an area known to be high in selenium is consumed.
The UL for adults for selenium is 400 µg/day. Individuals who regularly consume more than 400 µg/day may be at risk of adverse effects that include brittle nails and hair loss.
With careful consideration to the points mentioned above, the various Dietary Reference Intakes (DRIs) may be used to assess as well as to plan nutrient intakes. Box 9-1 summarizes the appropriate uses of the DRIs for individuals and groups.
AIN (American Institute of Nutrition). 1990. Nomenclature policy: Generic d scriptors and trivial names for vitamins and related compounds. J Nutr 120:12–19.
Briefel RR, Sempos CT, McDowell MA, Chien S, Alaimo K. 1997. Dietary methods research in the third National Health and Nutrition Examination Survey: Underreporting of energy intake. Am J Clin Nutr 65:1203S–1209S.