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EFFECT OF SEASON AND VITAMIN D SUPPLEMENTATION ON PLASMA CONCENTRATIONS OF 25‐HYDROXYVITAMIN D IN NORWEGIAN INFANTS

ABSTRACT. Plasma concentrations of 25‐hydroxyvitamin D (250HD) were determined in 81 vitamin D supplemented or unsupplemented infants at the end of winter. The values were compared with maternal levels and with concentrations found in 22 unsupplemented infants at the end of summer. The 250HD levels of the neonates were lower, but closely related to maternal values (r=0.95, p<0.0005). Unsupplemented breast‐fed infants had lower 250HD levels at 6 weeks than at 4 days (16±7 vs. 32±15 nmol/l, mean ±1 SD, p<0.0005). The mean 250HD level of vitamin D supplemented 6‐12 months old infants was intermediate between those of the unsupplemented nursed groups and the unsupplemented children studied during summer (53±28 vs. 85±28 nmol/l, p<0.0005). Six weeks old infants who had received a milk formula containing 400 IU vitamin D3 per liter had levels similar to the latter group (92±21 nmol/l). The data suggest that the vitamin D stores acquired during fetal life, or from ultraviolet light exposure during the summer, may be inadequate to maintain safe levels of 250HD throughout the winter, but that a daily supplement of 400 IU is adequate to establish concentrations in the summer range.