Vitamin D supplementation in elderly nursing home residents increases 25(OH)D but not 1,25(OH)₂D

Vitamin D metabolism in elderly individuals can be compromised by several mechanisms. We previously described reduced concentrations of 1,25-dihydroxyvitamin D [1,25(OH)2D] in 30% of elderly nursing home residents. The present study assess the effect of vitamin D supplementation on 25-hydroxyvitamin D [25(OH)D] and 1,25(OH)₂D. We performed a double-blind study in which 30 elderly nursing home residents were randomly given either 50 μg vitamin D or a placebo daily for 6 wk. Vitamin D metabolites, immunometrically assayed parathyroid hormone (IRMA-PTH), ionized calcium, and bone Gla hormone (BGP) were measured in serum at baseline and biweekly for 6 wk. Serum 25(OH)D concentrations increased significantly (P < 0.0001) over the 6 wk in the treatment group but were unchanged in the placebo group. Serum 1,25(OH)₂D, ionized calcium, BGP, and PTH were not significantly altered by the supplement. We conclude that vitamin D supplementation results in an increase in circulating 25(OH)D but not 1,25(OH)₂D; however, the long-term effect on bone mineral metabolism remains unclear.