Effectiveness of selenium supplements in a low-selenium area of China

Background: Selenium is an essential micronutrient with a recommended dietary allowance for adults of 55 mu g/d. It functions as an essential constituent of selenoproteins. Although there is no evidence of selenium deficiency in the United States, people in many other areas of the world are selenium deficient, with the consequence that they are unable to express their selenoproteins fully. Objective: We carried out a supplementation trial in a selenium-deficient population in China to assess the requirement for selenium as selenite and as selenomethionine. Design: One hundred twenty subjects with an average selenium intake of 10 mu g/d were randomly assigned and administered tablets containing no selenium or amounts as high as 66 mu g Se/d for 20 wk. Plasma was sampled before supplementation and at 4-wk intervals during supplementation and was assayed for the 2 plasma selenoproteins, glutathione peroxidase and selenoprotein P. Results: Full expression of glutathione peroxidase was achieved with 37 mu g Se/d as selenomethionine and with 66 mu g/d as selenite. Full expression of selenoprotein P was not achieved at the highest doses of either form. Conclusions: Full expression of selenoprotein P requires a greater selenium intake than does full expression of plasma glutathione peroxidase. This suggests that selenoprotein P is a better indicator of selenium nutritional status than is glutathione peroxidase and that the recommended dietary allowance of selenium, which was set with the use of glutathione peroxidase as the index of selenium status, should be revised. Selenium as selenomethionine had nearly twice the bioavailability of selenium as selenite.