Effects of postmenopausal hormone replacement therapy with and without vitamin D3 on circulating levels of 25-hydroxyvitamin D and 1,25-dihydroxyvitamin D

The effects of postmenopausal hormone replacement therapy (HRT) and vitamin D-3 on vitamin D metabolites (25OHD and 1,25(OH)(2)D) were studied in a population-based prospective 1-year study. The serum concentrations 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 placebo group (calcium lactate 500 mg/day). Serum samples were taken in March-Api-il when vitamin D formation from sunlight in Finland is minimal after the dark winter, Serum concentrations of 25OHD increased in the 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 placebo 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 concentrations of PTH decreased by 23.2% (P < 0.05) in the placebo group, but did not change significantly in the other three groups. The concentrations of serum calcium increased in the nonhormone groups (P < 0.001), whereas serum phosphate concentrations decreased in the hormone groups (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 even though the initial levels were low, Interestingly, the combination of HRT and vitamin D-3 did not increase serum calcitriol concentrations as much as HRT alone.