MuscleRulz Vitamin D-3 is an essential vitamin for many metabolic processes. Vitamin D-3 helps to regulate the absorption of calcium and phosphorous, and supports normal immune system function. It Supports Healthy Bones, Teeth and Immunity. Without Vitamin D-3, you may be missing out on the benefits of the calcium in your diet, and most people start taking Vitamin D-3 after they experience signs of deficiency. However, it is not abundant in food. As more people avoid sun exposure, Vitamin D-3 supplementation becomes even more necessary to ensure that your body receives an adequate supply. Supports Healthy Bones, Teeth and Immunity Regulate the absorption of calcium and phosphorous Supports normal immune system function Essential vitamin for many metabolic processes