Dietary Supplement For Bone and Immune HealthSunlight is the source of life on Earth, but we may not be away of all the ways it benefits us. Our bodies manufacture vitamin D-3 when the skin is exposed to UV radiation from sunlight, but the ability to do so decreases as we age. Vitamin D-3 helps maintain healthy calcium and phosphorus levels in the body for strong bones, it supports muscle strength in older adults and it also plays an active role in a healthy immune response. Vitamin D-3 (cholecalciferol) is the optimal form of vitamin D. It is the form of vitamin D that the body manufactures in sunlight, and the form most efficient for the body's needs.