RESUMEN
Vitamin D and its metabolites were determined in cow's milk, infant formulas, and colostrum, transitional and mature breast milk by specific protein-binding assays following HPLC (high-pressure liquid chromatography). Cow's milk contains (mean +/- SEM) 50.4 +/- 4.1 pg/ml vitamin D (n = 10), 499 +/- 47 pg/ml 25-OH D (n = 10) and 9.7 +/- 1.0 pg/ml 1,25 (OH)2D (n = 3). 86.6% of the added vitamin D3 was recovered from infant formulas. The mean content (mean +/- SEM) of 25-OH D and 1,25(OH)2D of infant formulas are 299 +/- 35 pg/ml and 5.4 +/- 0.9 pg/ml (n = 9), respectively. Vitamin D concentration of colostrum and mature breast milk is 122 +/- 3.4 pg/ml (n = 7, mean +/- SEM) and 38 +/- 3.3 pg/ml (n = 9) respectively; the 25-OH D content increases from 294 +/- 50.6 pg/ml (n = 10) to 845 +/- 190 pg/ml (n = 14) during lactation. The increase of 1,25-(OH)2D from early to mature breast milk (3.2 +/- 0.6 pg/ml, n = 8 versus 5.3 +/- 0.7 pg/ml, n = 20) is still statistically significant.