Vitamin D, is also known as calciferol or cholecalciferol. When parents send their children out in the sun to play, they're not just trying to get them out of the house. They know that sunlight forms this vitamin in the skin (actually, it's ultraviolet radiation that does it). Indeed, most people can manufacture enough vitamin D in summer to last them through the winter and there's little danger of overdosing on sunlight vitamin D because the body limits the amount formed. Why is vitamin D important? It facilitates the absorption of calcium in the body, regulates calcium and phosphorus metabolism in the body and thus helps build strong bones and teeth. In the old days, children in cold climates with limited sunshine often suffered from rickets, an acute vitamin D deficiency most often manifested as bowlegs and deformed ribs