Selenium Intake And Status In Health & Disease

Abstract

Selenium (Se) is an essential trace element that is incorporated into selenoproteins with a wide range of health effects1. Low selenium status has been associated with Keshan and Kaschin-Beck diseases, viral virulence, higher risk of mortality, prostate cancer, autoimmune thyroid disease and cognitive decline, poorer immune function and reproductive success. Higher Se status or Se supplementation has been shown to have anti-viral effects, to be essential for successful male and female reproduction and to reduce thyroid autoimmunity. In a large observational Chinese study, we recently found a significantly higher prevalence of thyroid disease in low-Se counties of Shaanxi Province than in moderate-Se counties in that same province2. Prospective studies have generally shown some benefit of higher Se status on the risk of prostate, lung, colorectal, and bladder cancers but trials have had mixed findings, likely highlighting the fact that supplementation will only confer benefit if intake of a nutrient is inadequate. Supplementation of people who already have adequate intake with additional Se has been shown to increase the risk of alopecia, dermatitis, non-melanoma skin cancer, prostate cancer, type-2 diabetes and mortality. Our recent randomised controlled trial in Denmark, a country of low-moderate Se status, showed significantly increased mortality with a Se dose of 300 µg/d after five years of treatment and a further ten years of follow-up. Long-term supplementation with a dose of 200 µg/d in a country of higher Se status, such as the US, might have a similar adverse effect. The crucial factor that needs to be emphasized with regard to the health effects of Se is the inextricable U-shaped link with status: while additional Se intake may well benefit people with low status, those of adequate-to-high status may be affected adversely and should not take selenium supplements.