Clinical trials, future perspectives, and challenges of selenium supplementation and therapy

Selenium (Se) is a trace element with a complex and intriguing relation with human health. It is ubiquitous in the environment, and it occurs in both organic and inorganic compounds. Despite the involvement of selenoproteins in redox reactions and some potential for beneficial effects, experimental studies in humans and specifically randomized controlled trials have failed to demonstrate a preventive role of Se supplementation on cancer and other chronic diseases. Conversely, the occurrence of adverse effects such as increased risk of type 2 diabetes, endocrine and cardiometabolic disorders has raised concerns about the safety of this element. This study aims to provide an overview of the effects of Se supplementation in humans, with reference to immunological and metabolic endpoints, and chronic disease risk and the relevance of the chemical form of the element in determining both its toxicological and nutritional properties.