What does Vitamin D do? The link between vitamin D and strong healthy bones was made many years ago when doctors realized that sunlight, which allows you to produce vitamin D, or taking cod liver oil, which contains vitamin D, helped to prevent rickets in children. Get the best vitamin D online at Lifestyle Markets. Today, vitamin D is seen as a vital part of good health and it’s important not just for the health of your bones. Recent research is now showing that vitamin D may be important in preventing and treating a number of serious long term health problems.