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Abstract
This ancillary study aimed to examine the effects of vitamin D supplementation on serum IGF-I and vitamin D metabolites in healthy adolescents over 12 weeks. Relationships between IGF-I and 25(OH)D, 1,25(OH)2D, and iPTH were examined using Pearson correlations and nonlinear regression analysis. There were no significant relationships between change in vitamin D metabolites and IGF-I. However, a significant interaction was observed between sex and change in serum 1,25(OH)2D over 12 weeks on changes in serum IGF-I (P=0.04). When probed, the interaction effect of sex approached significance in opposite directions for males (t=-1.9, P=0.05); and females (t=1.7, P=0.07). Our data suggests that vitamin D supplementation does not effect changes in IGF-I in healthy children, but there is a sex-dependent link between 1,25(OH)2D and IGF-I. The reason for the interaction is unclear, but additional studies are needed to explore the varied IGF-I-1,25(OH)2D relationships in males and females with vitamin D supplementation.