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

Randomized placebo-controlled study in healthy adult men and women aged 18 years or older living in a selenium-deficient area of Mianning County, Sichuan Province, China. Each active selenium dose group was assigned 10 participants, and tablets were administered under supervision each morning for 20 weeks.

This was a dose-ranging oral selenium tablet trial with two active forms: L-selenomethionine and sodium selenite. Each active group took one supervised tablet each morning for 20 weeks; measured tablet selenium contents ranged from 13 to 61 micrograms Se/day for selenomethionine and 15 to 66 micrograms Se/day for selenite, compared with placebo.

Supplementation improved selenium biomarkers, but L-selenomethionine was more bioavailable and required a lower dose than sodium selenite to maximize glutathione peroxidase. Full expression of glutathione peroxidase was achieved with 37 micrograms Se/day as selenomethionine and with 66 micrograms Se/day as selenite, while selenoprotein P never reached full expression at the highest dose of either form. The highest average plasma selenium concentration reached 88 micrograms Se/L with selenomethionine versus 52 micrograms Se/L with selenite, and the highest average selenoprotein P concentration was only 75% of the US standard. The authors concluded that selenoprotein P may be a better biomarker of selenium status than glutathione peroxidase and that selenium from organic sources has substantially higher bioavailability.

Small dose-group size, with 10 participants assigned to each active selenium group, limits precision. Some selenite dose groups were combined because they were indistinguishable, no arm-specific analyzed Ns were reported for the active groups, and effect sizes, confidence intervals, and adverse events were not reported. Follow-up was only 20 weeks and the outcomes were biochemical biomarkers rather than clinical endpoints.