Relationship of total and calculated free 25-hydroxyvitamin D to biomarkers and metabolic indices in healthy children

ABSTRACT Context:  Vitamin D status is usually assessed by serum total 25-hydroxyvitamin D. Whether free 25-hydroxyvitamin D measures better correlate with various clinical outcomes is unclear. Objective: To identify correlations between total 25-hydroxyvitamin D (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. Design: Healthy urban-dwelling children underwent measurement of relevant variables. Setting: Academic medical center Participants: Healthy, urban-dwelling children, 6 months to 10 yrs old, predominantly of Hispanic background and representative of all common GC haplotypes. Intervention: None Main Outcome Measures: Total and free 25-OHD and 1,25(OH)2D, calcium, phosphate, PTH, glucose, insulin, aldosterone, and renin. Results: Mean t25-OHD [26.3±6.7ng/ml; 65.8±16.8nmol/L] were lowest in the GC2 genotype. Mean t1,25(OH)2D [57.6±16....