Washington: Vitamin D has been known to prevent rickets and promote healthy bones by regulating calcium levels in the body.

But it has been found to play a much broader role than thought previously, for example, in the proper functioning of the immune system and in development of the brain.

Evidence continues to pile suggesting that it also protects against autoimmune diseases, including multiple sclerosis and type I diabetes, as well as some forms of cancer, particularly colorectal and breast.

In fact, over 900 different genes are now known to be able to bind the vitamin D receptor, through which vitamin D mediates its effects.

In a definitive critical review, Joyce C. McCann, and Bruce N. Ames, of Children's Hospital Oakland Research Institute (CHORI) conclude that there is ample evidence to suggest an important role for vitamin D in brain development and function.

Vitamin D is present in only a few foods (e.g., fatty fish), and is also added to fortified milk, but our supply typically comes mostly from exposure to ultra-violet rays (UV) in sunlight.

UV from the sun converts a biochemical in the skin to vitamin D, which is then metabolised to calcitriol, its active form and an important hormone.

Formation of vitamin D by UV can be six times more efficient in light skin than dark skin, which is an important cause of the known widespread vitamin D deficiency among Afro-Americans living in northern latitudes.

Dark skin has been selected during evolution because it protects against the burning UV rays of the sun in the tropics. White skin has been selected for allowing as much UV exposure to make sufficient vitamin D in Northern (high) latitudes.

Thus, fair-skinned northerners are at risk in Australia or Arizona for sunburns and UV-induced cancer, while dark-skinned people in the Northern U.S. or European latitudes

These conclusions will appear on Tuesday in the Federation of American Societies for Experimental Biology Journal. IANS