Bone metabolism, density, and geometry in postmenopausal women with vitamin D insufficiency: a cross-sectional comparison of the effects of elevated parathyroid levels.

Abstract

In vitamin D insufficiency, elevated parathyroid hormone (PTH) levels may contribute to adverse effect on bone. We assessed effects of PTH responses to vitamin D insufficiency on bone metabolism, density, and geometry. Using a cross-sectional design, we investigated 102 healthy postmenopausal women with low 25-hydroxy-vitamin D (< 50nmol/L) levels, who had either secondary hyperparathyroidism with elevated PTH levels (> 6.9pmol/L, N = 51) or normal PTH levels (N = 51). Bone mineral density (BMD) and bone geometry were assessed by Dual-Energy X-ray absorptiometry (DXA), quantitative computed tomography (QCT) and high-resolution peripheral QCT (HRpQCT) scans. Bone metabolism was assessed by biochemistry including bone turnover markers. Levels of 25(OH)D were 38 (IQR 31-45) nmol/L with no differences between groups. PTH levels were 8.5 (IQR 7.5-9.5) in women with SHPT and 5.2 (4.4-6.6) pmol/L in women with normal PTH (p < 0.001). BMI and eGFR did not differ between groups. SHPT was associated with lower total- and trabecular bone area, lower cortical perimeter, and increased cortical area in tibia and radius. SHPT was associated with a lower weight-adjusted BMD at the lumbar spine (p < 0.05). High compared to normal PTH levels were associated with significantly lower plasma levels of 1,25(OH)2D, phosphate, but higher levels of osteocalcin and borderline higher levels of CTx. PTH correlated to osteocalcin and CTx. High PTH levels are associated with altered bone geometry, increased bone turnover, and reduced BMD at the spine. Whether an increased cortical thickness with a lower trabecular volume is an effect of PTH or not needs further elucidations.