Administration of a supplement containing both calcium and vitamin D is more effective than calcium alone to reduce secondary hyperparathyroidism in postmenopausal women with low 25(OH)vitamin D circulating levels

Background and aims: Supplementation of postmenopausal women with calcium alone or calcium-vitamin D association was suggested to have positive effects on bone turnover and bone density, as well as to lower fracture incidence. The beneficial effect appears to be mediated by a reduction in parathyroid hormone secretion. Our aim was to compare the respective efficacy of calcium and calcium-vitamin D supplements in reducing serum parathyroid hormone levels in postmenopausal women with prevalent low 25(OH)vitamin D levels. Methods: One hundred consecutive ambulatory postmenopausal women with serum 25(OH)vitamin D levels below 18 ng/mL were included in a randomized, prospective, open label study. For a duration of 90 days, the women were randomly assigned to a daily supplementation of either one tablet of calcium gluconolactate and carbonate (500 mg calcium), or one powder-pack of an association of calcium carbonate (500 mg calcium), citric acid (2.175 gr) and cholecalciferol (200 IU). Changes observed during the 90 days of the study in circulating PTH levels were the primary endpoint, while changes in serum 25(OH)D levels were assessed as secondary endpoint. Results: A significant difference was observed between the calcium-vitamin D (CaD) and the calcium (Ca) only groups for changes occurring during the 90 days of the study in PTH (-14.5 +/- 40% and +2.5 +/- 46%) (p=0.009) and 25(OH)D (+67 +/- 77% and +18 +/- 55%) (p<0.001) circulating levels. PTH changes between baseline and day 90 were significant in the CaD group, but not in the Ca group. The odds ratio for a patient in group Ca to experience an absolute (<12 ng/mL) deficiency in circulating 25(OH)vitamin D levels, compared to a group CaD patient was statistically increased (OR: 3.22, 95% CI: 1.33-7.80). Conclusions: Our results support the recommendation of supplementing postmenopausal women with low circulating levels of 25(OH)vitamin D with a combination of calcium and vitamin D, rather than with calcium alone.