Vitamin D, calciferol, is a fat-soluble vitamin. It is known as the “sunshine” vitamin because it is formed in the body by the action of the sun’s ultraviolet rays on the skin. Vitamin D is converted in the kidneys to the hormone calcitrol, which is actually the most active form of vitamin D. The effects of this hormone are targeted at the intestines and bones.
Vitamin D requirements increase with age, while the ability of skin to convert sunlight into Vitamin D decreases. In addition the ability of the kidneys to convert calcidiol to its active form also decreases with age, prompting the need for increased Vitamin D supplementation in elderly individuals. One billion people in the world are currently Vitamin D deficient.
The major biologic function of vitamin D is to maintain normal blood levels of calcium and phosphorus. Vitamin D aids in the absorption of calcium, thereby helping to form and maintain strong bones. It promotes bone mineralisation in conjunction with a number of other vitamins, minerals, and hormones. Without vitamin D, bones can become thin, brittle, soft, or misshapen. Vitamin D prevents rickets in children and osteomalacia in adults, which are skeletal diseases that result in defects that weaken bones.