Methods of assessment of selenium status in humans: a systematic review.

Systematic review of human supplementation studies assessing biomarkers of selenium status. Evidence came from 18 studies in mostly healthy adults, with participants drawn from low-selenium and other diverse settings; some studies enrolled women with unexplained infertility, smokers, people with muscular complaints, or populations with low baseline selenium status.

Active interventions were selenium supplementation regimens used to probe biomarker responsiveness, most commonly selenomethionine or selenium-enriched/high-selenium yeast. Doses ranged from 10 to 703 μg selenium/day, with most studies lasting about 4 to 32 weeks; one study used a step-up regimen of 100 μg/day for 1 month then 200 μg/day for 1 month.

Selenium supplementation consistently changed several biomarkers, supporting plasma selenium, erythrocyte selenium, whole-blood selenium, plasma selenoprotein P, and plasma, platelet, and whole-blood glutathione peroxidase activity as useful indicators of selenium status. Plasma selenium increased with supplementation (WMD: 0.90 lmol/L; 95% CI: 0.67, 1.14; 14 studies, 512 participants), and similar pooled increases were seen for erythrocyte selenium, whole-blood selenium, urinary selenium, GPx activity, and plasma selenoprotein P. Evidence was insufficient for urinary selenium, plasma T3:T4 ratio, thyroxine, total homocysteine, hair/toenail selenium, and erythrocyte or muscle GPx activity. The authors concluded that more standardized, high-quality randomized trials are needed to define biomarker performance across populations, baseline status, doses, duration, and genotype.

The evidence base was heterogeneous, with widely varying selenium forms, doses, populations, and intervention durations. Many outcomes were informed by small studies or limited datasets, and several pooled analyses showed very high heterogeneity. Reporting of adverse events and some biomarker details was limited, and the review noted a need for standardized units and larger high-quality randomized trials.