Serum Concentrations of Vitamin D Metabolites in Exclusively Breast‐Fed Infants at 70° North

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Abstract
The effect of prolonged breasts-feeding on the serum concentrations of vitamin D metabolites, Ca, phosphate and alkaline phosphatase was studied longitudinally in 7 infants from northern Norway. They were exclusively breast-fed for a median of 7.5 mo. Of the mothers (3) were supplemented with vitamin D throughout lactation. All but 1 of the infants had 25-hydroxyvitamin D (25-OHD) levels in the rachitic range (< 20 nmol/l) on at least 1 occasion. Vitamin D supplementation of the mother had no apparent effect on the infants'' 25-OHD levels, but the values increased during summer. The infant who had the lowest 25-OHD levels also had decreased 1,25-dihydroxyvitamin D (1,25-(OH)2D) concentrations, while the others maintained 1,25-(OH)2D levels within normal limits. [24,25-dihydroxyvitamin D] 24,25-(OH)2D concentrations were undetectable when the 25-OHD levels were < 35 nmol/l, but the 2 metabolites were closely correlated for higher values of 25-OHO. Low 25-OHD levels were associated with decreased phosphate concentrations at 6 mo. The Ca levels were normal throughout the study period of 1 yr, as were all but 2 of the alkaline phosphatase values. Although none of the infants had clinical or biochemical evidence of rickets, the results suggest that the vitamin D supply from human milk is inadequate and that routine vitamin D supplementation is advisable for breast-fed infants who are deprived of sunlight exposure.

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