Parathyroid hormone response to severe vitamin D deficiency is associated with femoral neck bone mineral density: an observational study of 405 women with hip-fracture

OBJECTIVE: Hip-fracture patients with vitamin D deficiency can have either secondary hyperparathyroidism or normal levels of parathyroid hormone (PTH). We hypothesized that bone mineral density (BMD) could be lower in patients with high PTH levels than in those with normal levels of PTH, irrespectively of the severity of vitamin D depletion. DESIGN: In this cross-sectional study, we examined 405 women who had serum 25-hydroxyvitamin D below 12ng/ml 20.0 +/- 5.9 (mean +/- SD) days after a hip-fracture. PTH was assessed by a chemiluminescent immunometric assay and BMD by dual-energy x-ray absorptiometry at the unfractured femoral neck. RESULTS: BMD was significantly lower in the 148 women with secondary hyperparathyroidism than in the 257 with normal PTH levels: the mean T-score (SD) was -2.88 (0.93) and -2.65 (0.83), respectively, in the two groups (mean difference 0.23; 95% CI 0.05 - 0.41; P = 0.010). The association between PTH status and BMD persisted after adjustment for age, body mass index, phosphate, albumin-adjusted total calcium, 25-hydroxyvitamin D, estimated glomerular filtration rate, and magnesium (P = 0.01). The presence of secondary hyperparathyroidism was significantly associated with a femoral neck T-score lower than -2.5. The adjusted odds ratio was 1.81 (95% CI 1.11 - 2.95; P = 0.017). CONCLUSION: Our results show that PTH levels in the presence of severe vitamin D deficiency were significantly associated with femoral BMD in women with hip-fracture. Prevention and treatment of vitamin D deficiency may be particularly relevant in women who develop secondary hyperparathyroidism.