EFFECTS OF POSTMENOPAUSAL HORMONE REPLACEMENT THERAPY WITH AND WITHOUT VITAMIN-D-3 ON CIRCULATING LEVELS OF 25-HYDROXYVITAMIN-D AND 1,25-DIHYDROXYVITAMIN-D

The effects of postmenopausal hormone replacement therapy (HRT) and vi tamin D-3 on vitamin D metabolites (25OHD and 1,25(OH)(2)D) were studi ed in a population-based prospective 1-year study. The serum concentra tions of intact parathyroid hormone (PTH), calcium, and phosphate were also studied. A total of 72 women were randomized into four treatment groups: HRT group (sequential combination of 2 mg estradiol valerate and 1 mg cyproterone acetate), Vir D-3 group (vitamin D-3 300 IU/day calcium lactate 500 mg/day), HRT + Vit D-3 group (both above) and pla cebo group (calcium lactate 500 mg/day). Serum samples were taken in M arch-Api-il when vitamin D formation from sunlight in Finland is minim al after the dark winter, Serum concentrations of 25OHD increased in t he Vit D-3 group (33.5%, P < 0.001) and in the HRT + Vit D-3 group (38 .2%, P < 0.001) but had not changed significantly in the HRT and place bo groups at the I-year follow-up examination. Serum concentrations of calcitriol (1,25(OH)(2)D) increased, however, only in the HRT group ( 23.7%, P < 0.05), and remained unchanged in other groups. Serum concen trations of PTH decreased by 23.2% (P < 0.05) in the placebo group, bu t did not change significantly in the other three groups. The concentr ations of serum calcium increased in the nonhormone groups (P < 0.001) , whereas serum phosphate concentrations decreased in the hormone grou ps (P < 0.05 and 0.001), Our results confirm the positive effect of 1 year of HRT an serum calcitriol, Vitamin D-3 supplementation increased 25OHD concentrations, bur did not affect calcitriol concentrations ev en though the initial levels were low, Interestingly, the combination of HRT and vitamin D-3 did not increase serum calcitriol concentration s as much as HRT alone.