O r i g i n a l A r tic le 266 I NTRO D U C TIO NBreast milk is the single best food source for infants. However, the breast milk of mothers on normal diets only contains 25-78 IU/L of vitamin D and is therefore insufficient as a source of vitamin D for infants.(1) The optimal blood level of 25-hydroxyvitamin D (25OHD) in newborns is as yet unknown.(1,2) However, it is generally accepted that a serum 25OHD level of 11 ng/mL in newborns is sufficient to prevent rickets (2,3) and that a serum 25OHD level of more than 30 ng/mL is necessary to control secondary hyperparathyroidism as well as increase calcium absorption. Serum 25OHD levels of more than 30 ng/mL are accepted as ideal, and 25OHD levels less than 20 ng/mL are considered deficient. [6][7][8][9][10] In view of such studies, we attempted to determine the time needed to attain sufficient levels of serum 25OHD in vitamin D-deficient newborns on two different vitamin D