Current Insights and Research Gaps in Selenium Supplementation for Metabolic Health: A Scoping Review

Selenium plays a crucial role in maintaining metabolic health, providing antioxidant protection, and modulating inflammation. Further clarification of the physiological functions and pathological relevance of selenium is necessary to increase understanding of its therapeutic potential through supplementation and to determine the most effective strategies across different populations and metabolic conditions. We sought to systematically map and synthesize existing evidence on the effects of selenium supplementation on inflammation, oxidative stress, and glucose-lipid metabolism in adult populations, and to identify knowledge gaps that hinder the establishment of safe and effective selenium dosing guidelines. A scoping review was conducted based on the Preferred Reporting Items for Systematic reviews and Meta-Analyses Extension for Scoping Reviews (PRISMA-ScR) guidelines, in which we searched for the major electronic databases to identify clinical trials that evaluated the effects of selenium supplementation on standard features of metabolic disease among diverse adult population groups. Improvements in metabolic markers were observed, particularly in studies addressing diabetes and insulin resistance (up to a 26% reduction in Homeostatic Model Assessment of Insulin Resistance [HOMA-IR])), and inflammation (with up to a 62.4% reduction in high-sensitivity C-reactive protein [hs-CRP]). The benefits were seen in reported studies with intervention durations of 12 weeks or longer. In limited studies, selenium had neutral effects in a trial of polycystic ovary syndrome (PCOS) and an adverse effect in 1 postmenopausal trial, indicating that results in these groups remain inconclusive. Co-supplementation with probiotics or antioxidants had beneficial effects in some studies. Selenium supplementation has been observed to improve insulin sensitivity, lower hs-CRP, and enhance antioxidant defenses, particularly in adults with diabetes or insulin resistance, while effects in PCOS and postmenopausal women remain equivocal. Because both deficiency and excess of selenium can be harmful, dosing must be guided by baseline selenium status. Harnessing this narrow therapeutic window could enhance metabolic care, but long-term, well-controlled trials are still needed to define optimal regimens and clarify who stands to benefit most.