Background: Vitamin D deficiency and hyperparathyroidism is associated with bone loss. However, it is less clear whether serum levels of Vitamin D, parathyroid hormone (PTH) and calcium are associated with fracture risk, and if so, whether it is mediated through increasing cortical porosity and thickness. We tested whether lower vitamin D and higher PTH and calcium levels were associated with fracture independent of these cortical features.
Methods: We measured serum 25 (OH) Vitamin D, PTH and total calcium, femoral neck areal bone mineral density (FN aBMD) using densitometry (DXA), and femoral subtrochanteric cortical porosity, cortical thickness, and trabecular bone volume/tissue volume (BV/TV) using StrAx1.0 software in 211 postmenopausal women aged 54-94 years with non-vertebral fractures and 232 controls.
Results: Women with fracture exhibited lower serum levels of vitamin D (76.4 vs. 82.9 nmol/L), higher PTH (4.58 vs. 4.13 pmol/L), and total calcium (2.43 vs. 2.35 mmol/L) than controls, higher porosity of the total cortex (43.8 vs. 41.7%), compact cortex (35.3 vs. 34.3%), transitional zone (59.3 vs. 58.4%), and reduced cortical thickness (4.06 vs. 4.36 mm), p < 0.05, but not lower trabecular BV/TV (0.266 vs. 0.272%), p=0.81. Each standard deviation (SD) decrease in vitamin D and each SD increase in PTH and calcium was associated with increased odds for fracture (OR 1.31 95% confidence interval (CI) (1.07-1.61), 1.28 (1.04-1.58) and 1.78 (1.41-2.24), p < 0.05, respectively after adjustment for age, height, weight, femoral subtrochanteric cortical porosity and thickness. Higher calcium levels, but not vitamin D and PTH remained associated with fracture after mutual adjustment, even after additional adjustment for FN aBMD (OR 1.85; 1.45-2.35, p < 0.001).
Conclusion: Calciotropic hormones are associated with increased odds for fracture, independent of cortical bone architecture. These findings are suggesting that calciotropic hormones may increase the risk of fracture through other mechanisms.
Disclosure: EF Eriksen reported that his research has been supported by Amgen, Novartis, Eli Lilly and IDS. A Bjornerem has received lecture fees from Eli Lilly. All authors state that they have no other conflict of interest. The North Norwegian Health Authorities funded the study (ID 5645 1002-11, ID 9167/SFP1090-13, ID 9168/SFP1135-13) but had no role in design and conduct of the study; in the collection, analyses, and interpretation of the data; or in the preparation, review, or approval of the manuscript.