viduals in the same supplemented group. Selenium supplementation increased the plasma glutathione peroxidase activity because the increase in the activity relative to presupplementation was apparent for nearly every supplemented individual. However, the increase at the lowest level tested (10 µg [0.13 µmol]/day) could not be statistically differentiated from the increase at the highest level tested (40 µg [0.51 µmol]/day). Thus, choosing to be conservative, an EAR of 38 µg (0.48 µmol) (28 µg [0.35 µmol]/day from food + 10 µg [0.13 µmol]/day from the lowest level supplemented) was selected.

Summary. Calculation of an EAR for selenium is based on the results of two intervention studies that were done in different countries but had similar designs. The Chinese study suggests that a plateau of plasma glutathione peroxidase activity was reached with a selenium intake of 41 µg (0.52 µmol)/day. With a weight adjustment for North American males, the selenium intake was 52 µg (0.66 µmol)/day. The New Zealand study can be interpreted to suggest an EAR in the vicinity of 38 µg (0.48 µmol)/day. The average of those studies, 45 µg (0.57 µmol), has been chosen as the EAR.

Based on the criterion of maximizing plasma glutathione peroxidase activity, the data described above support a selenium EAR of 45 µg/day for the age group 19 through 50 years based on the weights of North American men. Given the reported greater susceptibility of women to develop Keshan disease and the fact that the data used to set the EAR came largely from men, selenium requirements for both males and females are based on the higher reference weights for males.

The RDA for selenium 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 selenium; 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 (there-