Vitamin D is required for your body to absorb calcium and stimulate bone formation. Vitamin D deficiency causes soft bones in youngsters (rickets) and brittle, deformed bones in adults (osteomalacia). Vitamin D is also required for several vital biological activities. Your body can make some vitamin D if you are exposed to sunlight or wear certain clothes (eg, no sunscreen, no dark clothing). Your body absorbs vitamin D when it interacts with the fat in your skin. The amount that you absorb depends on how much fat there is on the surface of your skin. Skin that is very oily will allow more vitamin D to be absorbed than skin that is dry. Dark-skinned individuals require more sun exposure than light-skinned people to make adequate amounts of vitamin D. Individuals with chronic liver disease may need a supplement if they do not get enough from their diet. People who work at desks all day without leaving their offices may be at risk for vitamin D deficiency. Those who work behind computer screens may be limited to making only if they expose themselves to sunlight for half days during the summer months. The best source of vitamin D is sunshine! However, because most people are not getting enough sun, supplements are needed to meet their needs.