Vitamin D is an important vitamin and helps build and maintain strong bones, teeth, and muscles. It also contributes to the normal function of the immune system. Vitamin D is produced in the body when ultraviolet B (UVB) rays from sunlight hit the skin. You also get vitamin D directly from foods, but it is generally difficult to obtain adequate levels from foods alone. During winter, in combination with today’s typically indoor lifestyles, deficiencies of vitamin D may occur. Vitamin D supplementation can be an effective way to fill this gap and give your body the vitamin D it needs.