Vitamin D: can an upper limit be defined?

Vitamin D ingested in excess results in hypercalcemia, which is caused by excessive absorption of massive quantities of calcium by the intestine and enhanced bone resorption. The symptoms of this intoxication include feeding difficulties, polydypsia, polyuria, irritability, lassitude and poor weight gain. Because daily intakes of 400 IU (10 microg) of vitamin D2 or D3 are completely safe, and because as low as 100 IU (2.5 microg) daily may prevent rickets, it is difficult to justify recent studies that attempt to firmly establish an upper limit of daily vitamin D intake in the normal neonate. Thus, despite efforts to better understand the upper limits of daily vitamin D intake, a concentration of 100 IU (2.5 g) of vitamin D per 100 kcal ingested, as is currently recommended by the Committee on Nutrition of the American Academy of Pediatrics, seems entirely appropriate.