promotes the normal functioning of the immune system helps to maintain bone in the normal state contributes to normal muscle function contributes to normal absorption/the absorption of calcium and phosphorus helps normalize the level of calcium in the blood helps maintain teeth in normal condition participates in cell division Vitamin D, also called cholecalciferol, can be formed by the human body on its own. The condition for this is getting enough UV light on the skin. Therefore, vitamin D is often referred to simply as “solar vitamin”. So, for a sufficient supply of vitamin D in the body, you need sunlight. The ultraviolet spectrum of sunlight provides the conversion of provitamin to its active form.