Define Functions of selenium in humans?

Until recently, the only known metabolic role of selenium in humans was as a component of glutathione peroxidase which along with vitamin E and superoxide dismutase forms a part of the and-oxidant defense system. However, more selenoproteins are being discovered and currently it is estimated that 50-100 selenoproteins are present in animals. Selenoproteins in animals and humans are involved in protection from oxidative damage, maintaining adequate thyroid hormone status and protection from injury by a heavy metal like mercury. Three major enzyme systems in which selenium plays an important role have been identified in humans.

These include:

a) Glutathione peroxidases,

b) Iodothyronine deiodonases, and

C) Selenoproteins P and W