VITAMIN-D AND MINERAL METABOLISM IN THE VERY-LOW-BIRTH-WEIGHT INFANT RECEIVING 400-IU OF VITAMIN-D

To examine (1) the effect of vitamin D intake (380 to 480 IU daily) on plasma 25-hydroxyvitamin D (25-OHD) and 1,25-dihydroxyvitamin D (1,25-(OH)2D) concentrations and (2) the relationship of 1,25-(OH)2D to calcium and phosphorus absorption and retention in the very low birth weight infant receiving a preterm infant formula. Subjects: Eleven "well" infants with a birth weight and gestational age (mean ± SD) of 1078±128 gm and 29±1.9 weeks, respectively, were studied for a 3-week period. Weight and postnatal age (mean ± SD) at the beginning of the study were 1132±56 gm and 16±6 days, respectively. All infants were fed a preterm infant formula and tolerated a full enteral intake (120 kcal/kg/day) for the duration of the study. Interventions: Plasma 25-OHD and 1,25-(OH)2D concentrations were measured at the beginning of the study and at the beginning of each 48-hour balance period. Calcium and phosphorus balance studies (n=33) were performed weekly. Main results: Plasma 25-OHD (30±10 ng/ml) and 1,25-(OH)2D (54±14 pg/ml) concentrations were normal at the beginning of the study. Plasma 25-OHD values did not change, but 1,25-(OH)2D values increased (p<0.001) throughout the study. Plasma 1,25-(OH)2D concentrations were not related to calcium or phosphorus absorption and retention, but were a linear function of postconceptional age. Conclusions: Normal vitamin D status and activity are maintained in the very low birth weight infant fed a high calcium formula (380 to 480 IU of vitamin D daily). Plasma 1,25-(OH)2D concentrations are not related to calcium absorption but are linearly related to maturity. © 1990 The C.V. Mosby Company.