Vitamin D, is a lipid- soluble vitamin obtained from both exogenous and endogenous sources. Vitamin D3 is found naturally contains vitamin D, but other dietary sources of Vitamin D are from the fortified foods, like milk and cereals, or from nutritional supplements. In recent years, rickets and Osteomalacia are reappearing, not only in temperate zones with limited sunshine but also in sunnier climates such as Australia, the USA, Ethiopia, Lebanon and Saudi Arabia. Research results strongly suggested that 1,25-(OH)2D3 may have a direct action through its receptor in the parathyroid glands, The presence of receptor has led to a study of the possible function of vitamin D in these organs. A good example of a new function described for 1,25-dihydroxyvitamin D3 is that found in the parathyroid gland, this is also true for the role of vitamin D hormone in skin, the immune system, a possible role in the pancreas, i.e., in the islet cells, and a possible role in female reproduction. Many studies have examined the relationship between Vitamin D levels and cardiovascular disease, metabolic, immune system and cancer risk. With the reemergence of hypovitaminosis D among adults and elderly age group, questions regarding the most appropriate treatment regimen require clarifications. Multiple treatment regimens have been proposed to treat hypo-vitaminosis D in young children and adults, including the daily or weekly, yearly orally and parental routes. New megadoses therapies have been used recently. We would like to highlight the recent evidence regarding their uses and safety.