Diabetes is one of the most common diseases affecting human health in the world, and insulin resistance has been recognized as an important contributor to the generation of type 2 diabetes, accounting for 90% of diabetes. Selenium, an essential trace element in human nutrition, is closely related to human health through incorporation into selenoproteins which have a wide range of important biological functions. In recent years the studies focusing on the relationship between selenium and diabetes have attracted much attention. Earlier studies showed that selenium has insulin-like effects, and thus may be promising in the prevention and treatment of diabetes. However, recent human trials and animal studies provided evidence that selenium plays a dual role in the initiation and development of diabetes, and long-term selenium supplementation unexpectedly increases the risk of insulin resistance and type 2 diabetes. Furthermore, the dual effect of selenium in the initiation and development of diabetes might be associated with a variety of selenoproteins, such as glutathione peroxidase 1 (GPx1), selenoprotein S (SelS) and selenoprotein P (SelP). This review summarizes the dual effect of selenium in diabetes, and the roles of selenoproteins in the initiation and development of diabetes. The prospect of this field is addressed as well.

Contents
1 Introduction
2 The insulin-like effects of selenium and the underlying mechanisms
3 Critical role of selenium in initiation and development of diabetes
4 Role of selenoproteins in initiation and development of diabetes and the underlying mechanisms
5 Conclusion and outlook