1983). Tap water is routinely used throughout the United States and Canada to raise selenium-deficient experimental animals. This is evidence that it contains very little selenium. In specific locales, however, water wells have been shown to supply much greater amounts of selenium. This is thought to result from irrigation practices, mining, or the presence of selenium-containing rocks (Valentine et al., 1978). Such high-selenium water supplies appear to be very limited and do not contribute to the selenium intake of large numbers of people (NRC, 1976).

Information from NHANES III on serum selenium concentrations in a free-living population is given in Appendix Table F-3. Serum or plasma selenium concentrations greater than the 0.8 to 1.1 µmol/L (7 to 9 µg/dL) plateau concentration are associated with maximization of plasma selenoproteins (Hill et al., 1996). The NHANES III median serum selenium concentration was 1.4 µmol/L (12.4 µg/dL) for 17,630 subjects aged 9 to more than 70 years. The first percentile was 1.1 µmol/L (9.5 µg/dL) and the ninety-ninth percentile was 1.9 µmol/L (16.3 µg/dL). This shows that at least 99 percent of these subjects should have had maximal concentrations of plasma selenoproteins. Thus, the NHANES III serum data and dietary intake data (based on food tables) collected from 1988 to 1992 indicate that the selenium requirement of its participants was being met.

In the United States or Canada, food is generally not fortified with selenium. An exception is proprietary infant formula that is designed to be the sole source of nutrients for the infant. Commercial formula manufacturers typically add selenium to ensure that infants consuming them will have an adequate selenium intake. Total selenium intakes from food plus supplements reported in NHANES III are found in Appendix Table C-7.

Selenium supplements of many strengths and types are available for purchase, and some popular multivitamin preparations contain selenium. However, according to NHANES III, selenium intake from both food (Appendix Table C-6) and food plus supplements (Appendix Table C-7) is above the EAR for most age groups in the United States. In the 1986 National Health Interview Survey, 9 per-