The relationship of 1,25-dihydroxyvitamin D and radial bone mass

We assessed the association between radial bone mass and vitamin D considering age, estrogen sufficiency and thiazide use in 373 women, aged 20-80 years in a geographically defined area. We measured cortical bone mass of the radius, using photon absorptiometry, and serum 25-hydroxyvitamin D and 1,25-dihydroxyvitamin D, using preliminary chromatography and protein-binding assay. We found that 1,25-dihydroxyvitamin D levels were higher in premenopausal women and postmenopausal women using estrogen replacement as compared to postmenopausal women (P less than 0.02). Users of thiazide-based antihypertensive medications had significantly lower 1,25-dihydroxyvitamin D than their age-matched peers (P less than 0.02). Dietary calcium intake was negatively associated with 1,25-dihydroxyvitamin D levels. Estimates of vitamin D intake from diet or sunlight were not associated with 1,25-dihydroxyvitamin D levels; nor were levels of 1,25-dihydroxyvitamin D related to 25-hydroxyvitamin D levels. 1,25-Dihydroxyvitamin D was negatively and significantly associated with radial bone mass, contributing approximately 6% of the explained variability of bone mass measurements. Together age, body size, thiazide use and 1,25-dihydroxyvitamin D accounted for about 47% of the explained variability in radial bone mass measurement. 1,25-Dihydroxyvitamin D was not associated with bone mass in women currently using a thiazide medication.