SINGLE-DOSE CHOLECALCIFEROL SUPPRESSES THE WINTER INCREASE IN PARATHYROID-HORMONE CONCENTRATIONS IN HEALTHY OLDER MEN AND WOMEN - A RANDOMIZED TRIAL

A randomized double-blind controlled trial of a single oral dose of 2. 5 mg (100 000 IU) cholecalciferol (vitamin D-3) was conducted in the w inter in 189 healthy free-living men and women aged 63-76 y. The mean baseline serum concentration for 25-hydroxyvitamin D was 34.5 nmol/L a nd for parathyroid hormone 3.18 pmol/L. After 5 wk, mean serum 25-hydr oxyvitamin D concentrations were 60% higher in the treated than in the placebo group (P < 0.001). There was a 12% difference in parathyroid hormone concentrations in the treated compared with the placebo group (P < 0.001). No differences in serum calcium were seen. Findings sugge st that 25-hydroxyvitamin D has a physiological role in the regulation of parathyroid secretion independent of serum calcium in healthy elde rly people. Parathyroid concentrations rise and 25-hydroxyvitamin D co ncentrations decline with age. These results may have implications for the prevention of osteoporotic fractures that occur with increased fr equency in winter and in elderly people.