ASSOCIATION OF FREE VITAMIN D3 CONCENTRATIONS AND ASTHMA TREATMENT FAILURES in the VIDA Trial

Vitamin D (vitamin D2 and vitamin D3) derived from sunlight exposure, diet or supplementation are converted to vitamin D2 (calciferol) and vitamin D3 (cholecalciferol) (25 (OH) D3) by vitamin D-25 hydroxylase (CYP2R1) in the liver, and subsequently converted to the biologically active 1,25-dihydroxyvitamin D2 and 1,25-dihydroxyvitamin D3 (25 (OH)2 D3) by CYP27B1 in the kidney and other tissue.1,2 Circulating total concentrations of vitamin D3 but not concentrations of active 1,25-dihydroxyvitamin D3 are used to define vitamin D status in part because of differences in total concentrations and half-life between the two metabolites.

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