BEIJING, CHINA. Deficiency of the micronutrient selenium is common in many developing countries. Selenium is of fundamental importance to human health, as it is an essential component of several major metabolic pathways, including thyroid hormone metabolism, antioxidant defence systems, and immune function. An intake consistently below the recommended dietary allowance (RDA) for adults of 55 micrograms per day could therefore have several potential public health implications.
Researchers from the Chinese Academy of Preventive Medicine measured the effects of selenium
supplementation in two forms: selenite, an inorganic salt, and selenomethionine, an organic form of
selenium. Selenomethionine is the major form of selenium found in food. They recruited 120 men and
women in China who were deficient in selenium, and monitored their selenium status by measuring plasma
levels of glutathione peroxidase and selenoprotein P. Before the study, the participants had an average
selenium intake of 10 mcg per day. They were randomized and given supplements for 20 weeks at various
doses from zero to 66 mcg per day, or placebo. Results showed that optimum levels of glutathione
peroxidase were reached with 37 mcg when given as selenomethionine, and with 66 mcg as selenite.
However, optimum levels of selenoprotein P were not reached at all, leading the researchers to conclude
that this is a better indicator of selenium nutritional status. Optimization of selenoprotein P would require
either a longer period of supplementation or higher doses, they suggest. They also point out that the RDA
was set based on studies using glutathione peroxidase, so propose that the recommendation should be
revised on the basis of selenoprotein P. Regarding the form of supplementation, the study demonstrates that
selenomethionine has nearly double the bioavailability of selenite and is thus superior for increasing
selenium status. This work supports previous studies which have demonstrated superior absorption rates
with selenomethionine as compared to selenite.