Bioavailability of selenium to Finnish men as assessed by platelet glutathione peroxidase activity and other blood parameters.

Three groups of 10 men of low selenium status were given 200 micrograms Se/day as Serich wheat, Se-rich yeast, or sodium selenate for 11 wk. Twenty unsupplemented subjects served as controls. Plasma Se levels increased steadily in the wheat and yeast groups for 11 wk without plateauing, whereas in the selenate group, plasma Se plateaued around 110 ng/ml after 4 wk. Platelet glutathione peroxidase (GSH-Px) activities increased rapidly in the wheat and selenate groups for 4 wk and then plateaued. Platelet GSH-Px increased more slowly in the yeast group. Ten weeks after the supplements were discontinued, platelet GSH-Px was higher in the wheat and yeast groups than in the selenate group. Assessment of Se bioavailability requires a short-term platelet GSH-Px measurement to determine immediate availability, a medium-term plasma Se measurement to estimate retention, and a long-term platelet GSH-Px measurement after supplements are discontinued to determine the covertibility of tissue Se stores to biologically active Se.