Calcium-regulating hormones and minerals from birth to 18 months of age: a cross-sectional study. I. Effects of sex, race, age, season, and diet on vitamin D status.

The influence of sex, race, age, season, and diet (cow's milk formula v human milk) on the vitamin D and vitamin D-binding protein status in infants less than 18 months of age was investigated in this cross-sectional, prospective study of 198 infants. No differences by sex were observed in serum 25-hydroxyvitamin D, 1,25-dihydroxyvitamin D, 24,25-dihydroxyvitamin D, or vitamin D-binding protein concentrations. By race, black infants had significantly elevated serum 1,25-dihydroxyvitamin D levels relative to white infants. By age, vitamin D-binding protein concentrations increased with increasing age. By season, serum 25-hydroxyvitamin D concentrations were low in winter, whereas 1,25-dihydroxyvitamin D and vitamin D-binding protein were high in winter compared with summer. By diet, formula-fed infants had higher serum concentrations of all measured vitamin D metabolites and vitamin D-binding protein than human milk-fed infants. Thus, race, age, season, and diet exert, individually or in combination, different and significant effects on vitamin D metabolites; these should be considered in assessing infant vitamin D status.