Vitamin D3 or cholecalciferol is a secosteroid and is structurally similar to steroids, such as testosterone and cholesterol. Depending upon its biochemistry and physiology, it has both inactive ( unhydroxylated cholecalciferol ) and active ( hydroxylated cholecalciferol at 1 and 25 position)forms in the body. The active form is actually a hormone and thus has profound effects on the body. It maintains the proper functioning of several body organs but its major function is to increase the blood calcium and phosphorus level by promoting their absorption from the intestines and then later to promote the reabsorption of calcium form the glomerular filtrate in the kidneys. In this way it has profound effects on the health of the bones by not only supporting the remodeling process but also proper bone mineralization.