Health effects of selenium supplementation: Chemical form and dose hold the key

Selenium (Se) has emerged as an essential micronutrient but its role in cancer prevention, immunomodulation, thyroid functioning and viral inhibition continues to remain inconclusive. The aim of this review is to dwell upon various factors responsible for mixed results arising out of Se supplementation trials. Some researchers have used inorganic form of Se, sodium selenite, which is less bioavailable and may be toxic if used for prolonged period, while others have opted for organic form, selenomethionine, which may incorporate non-specifically into proteins. In recent times, other organic forms, methylselenocysteine and selenocysteine, being less toxic, more bioavailable and endowed with greater therapeutic value against cancer have attracted the attention of research community. Moreover, appropriate dose (upto 200µg Se per day) may hold the key to bring perceptible beneficial health effects. Further, subjects used in trials should have low plasma Se levels for if they are already having its adequate level then supplementation is likely to be less effective. We conclude that the health effects of Se may largely depend upon its chemical form, dosage and Se-status of population being supplemented. Hence, these factors need to be taken in to account for future studies, trials of disease prevention and treatment by Se supplementation.