Standards and Requirements
One USP unit of vitamin D is taken as the activity of 0.025 Ilg of pure crystalline vitamin Ds' This is equal to the IV Other units have largely been dropped. The human requirements have not been established with accuracy. I his is not surprising, since the requirements are subject to so many variables. However, a number of clinical studies with infants and children have led to a fair understanding of the intake required to obviate symptoms and signs of suboptimal growth and bone development. The Food and Nutrition Board, National Research Council, sets the recommended intake at 400 IV per day for infants and at 400 IV daily during childhood. The allowance is set at 400 IU during pregnancy and lactation also.
Adults apparently have little or no need for the vitamin. Under certain dietary conditions,a vitamin requirement may be demonstrated. In many diseases of calcium and phosphorus metabolism the vitamin is beneficial. But under ordinary dietary conditions normal adults appear to maintain normal calcium and phosphorus metabolism without benefit of extra vitamin D.
