25-OHD response to vitamin D supplementation in children: effect of dose but not GC haplotype.

Objective: GC/DBP effects on response to vitamin D supplementation have not been well-studied. Thus we assessed free and total 25-OHD after vitamin D treatment across the six common GC haplotypes.

Design: This double-blind, randomized study compared two vitamin D3 doses in healthy, urban-dwelling 6-month to 10-year-old children at-risk for vitamin D deficiency.

Relationship of Total and Free 25-Hydroxyvitamin D to Biomarkers and Metabolic Indices in Healthy Children.

Context: Vitamin D status is usually assessed by serum total 25-hydroxyvitamin D (t25-OHD). Whether free 25-hydroxyvitamin D measures better correlate with various clinical outcomes is unclear.

Objective: To identify correlations between t25-OHD, calculated and direct measures of free 25-OHD, and to identify associations of these measures with other outcomes in children, across the 6 common GC haplotypes.