Influence of vitamin D status on vertebral fractures, bone mineral density, and bone turnover markers in normocalcemic postmenopausal women with high parathyroid hormone levels.

ABSTRACT

OBJECTIVE: The aims of the study were to analyze whether there is an association between serum PTH and the prevalence of vertebral fractures and its possible dependence on vitamin D status, and to assess the influence of serum 25-hydroxyvitamin D (25OHD) in the relationship between PTH and bone mineral density (BMD) or bone turnover markers (BTMs). DESIGN, PARTICIPANTS, AND SETTING: A total of 820 postmenopausal women were recruited after excluding those with any known condition that could influence serum PTH levels, except for a possible low serum 25OHD. Serum PTH and 25OHD concentrations, as well as vertebral fracture prevalence, BMD, and BTM (CTX and PINP) values were recorded. Serum PTH levels were divided into tertiles, and women were grouped into those in the highest tertile (>58 pg/ml) and those below. Serum 25OHD levels were stratified in 3 categories (<20, 20-30, and >30 ng/ml). RESULTS: Vertebral fracture prevalence was greater in women with PTH above 58 pg/ml (odds ratio [OR], 1.72; 95% confidence interval [CI], 1.04-2.84). After stratifying by 25OHD, this difference was only significant in women below 20 ng/ml (OR, 2.00; 95% CI, 1.02-3.87), those with 25OHD between 20 and 30 ng/ml showing a trend toward this (OR, 1.99; 95% CI, 0.92-4.36). Differences in BMD or BTM between women above and below 58 pg/ml of PTH were also observed only in those below 20 ng/ml. CONCLUSION: Elevated PTH levels are associated with increased prevalence of vertebral fractures, low bone mass, or higher BTM only in the presence of hypovitaminosis D. An adequate nutritional status in the vitamin appears to protect the bone from the deleterious effect of a high PTH.