Vitamin D is a vitamin that helps to maintain bone structure and regulate calcium levels in the body. Vitamin D formation is assisted through exposure to sunlight. For these reasons it may be used in patients, in supplement form, to treat conditions such as osteoporosis. Vitamin D may also be found in foods such as dairy products.Vitamin D is a nutrient that aids that absorption of important minerals from the body. These minerals include iron, calcium, zinc, magnesium, and phosphate. Many of these minerals are, in turn, vital for the integrity of bone. A deficiency in vitamin D, therefore, is associated with conditions such as osteoporosis, Paget's disease of bone, and rickets. Vitamin D is available as a supplement to counteract the effects of deficiency. Patients may also be advised to increase their exposure to sunlight, as sunlight assists the conversion of steroids beneath the skin into vitamin D forms. There are five different sub-types of vitamin D: D1, D2, D3, D4, and D5 - each of which plays a complementary role in the maintenance of bone health, among other factors.