Optimization of selenoprotein P and other plasma selenium biomarkers for the assessment of the selenium nutritional requirement: a placebo-controlled, double-blind study of selenomethionine supplementation in selenium-deficient Chinese subjects.

This was a placebo-controlled, double-blind, dose-ranging trial in healthy farmers aged 20-50 years from a selenium-deficient area of Mianning County, Sichuan Province, China. Ninety-eight participants were randomized across seven active dose groups, and 95 were analyzed after exclusions and loss to follow-up.

Healthy selenium-deficient adults were randomized to oral L-selenomethionine once daily for 40 weeks in seven dose groups: 0, 21, 35, 55, 79, 102, or 125 bcg Se/day. The regimen was delivered as 10 tablets per day, with tablet selenium content matching the assigned dose group.

Selenium supplementation increased plasma selenoprotein P and identified selenoprotein P as the best biomarker for selenium adequacy. Selenoprotein P was optimized by the 35-bcg Se/day dose, corresponding to a total daily selenium intake of about 49 bcg/d when dietary intake was estimated at 14 bcg/d. Glutathione peroxidase activity was optimized at the 21-bcg Se/day dose, or about 35 bcg/d total intake, while plasma selenium did not show a clear optimization pattern. No important adverse effects were detected.

The trial was conducted in a relatively small, single rural Chinese population with low baseline selenium intake, which limits generalizability. Outcomes were biomarker-based rather than clinical, and the study duration was 40 weeks with only 95 participants analyzed from 98 randomized. Dietary selenium intake was estimated indirectly, so some exposure misclassification is possible.