Natural Factors SunVitamin D3 - 1000 IU - Essential in the absorption of Calcium and Phosphorus, maintaining proper levels of Vitamin D in the body is critical for the development and maintenance of strong bones and teeth - particularly in growing children. Also important in later life for the prevention of osteoporosis and hypocalcemia, and as an immune booster and thyroid regulator, adequate quantities of this important vitamin should be part of everyone's diet.