Vitamin D is inadequate in many individuals and daily need appears to be higher than previously thought. The role of vitamin D in calcium metabolism and bone health is well known. However, it has many other important physiologic roles that are not as well appreciated. Vitamin D receptors are widely distributed in the body, including colon, prostate, breast and ovary, where it acts to inhibit the excessive growth of body cells and tissues and helps cells mature normally. Adequate amounts of vitamin D, an essential, fat-soluble vitamin, come from consistent exposure to sunshine and are difficult to obtain from dietary sources. Postmenopausal women, older individuals, and those with malabsorption, limited sun exposure, or certain illnesses may need higher intakes of vitamin D. Vitamin D3, the naturally occurring form, is supplied in high-potency amounts for those needing to conveniently augment dietary intake.