Bone metabolism characteristics and gender differences in patients with COPD: a cross-sectional study

Gender differences in bone metabolism of people with chronic obstructive pulmonary disease (COPD) remain unclear. We aim to explore the characteristics of bone metabolism and its clinical significance for patients with COPD.

A total of 564 cases (282 COPD cases and 282 controls) were preselected. Clinical and analytical characteristics of these cases were assessed. After excluding patients with other conditions known to disturb calcium metabolism, 333 patients (152 COPD cases and 181 controls) were identified. The medical records, indexes of bone turnover markers, serum calcium and phosphorus of the 333 patients were collected and their correlation was analyzed.

The 152 cases with COPD were 82.61 ± 7.745 years, 78.3% males, and the 181 age- and sex-matched control cases were 79.73 ± 11.742 years, 72.4% males. Levels of total procollagen type I amino-terminal propeptide (tPINP), osteocalcin (OC), serum calcium and phosphate were significantly lower (P < 0.001) while the level of parathormone (PTH) was significantly higher (P = 0.004) in COPD than in controls. The 25-hydroxycholecalciferol (25(OH)D₃) was below the lower limit of normal value (LLN) in both groups, which was significantly lower in COPD males than in control males (P = 0.026). In COPD group, PTH level was significantly higher in females (P = 0.006), and serum P was lower in males (P = 0.006). The adjusted linear regression analysis showed that the levels of tPINP, OC and serum Ca were decreasing greatly in COPD group [β (95%CI) - 8.958 (- 15.255 to - 2.662), P = 0.005; - 4.584 (- 6.627 to - 2.542), P < 0.001; - 0.065 (- 0.100 to - 0.031), P < 0.001]. Besides, smoke exposure, gender (male) were also related to hypocalcemia [β (95%CI) - 0.025 (- 0.045 to - 0.005), P = 0.017; - 0.041 (- 0.083 to - 0.001), P = 0.047], and 25(OH)D₃ was correlated with serum calcium, phosphorus, and PTH [β (95%CI) 15.392(7.032-23.753), P < 0.001; - 7.287 (- 13.450 to - 1.124), P = 0.021; - 0.103(- 0.145 to - 0.061), P < 0.001], and female was more likely to have secondary hyperparathyroidism [β (95%CI) 12.141 (4.047-20.235), P = 0.002].

COPD patients have remarkably low bone turnover (indicated by OC) and impaired bone formation (low tPINP), and they are also more prone to low calcium. Smoking and male may play roles in the formation of hypocalcemia, and the secondary hyperparathyroidism is more significant in COPD women. There may be gender differences in bone metabolism abnormalities and their mechanisms of COPD. The conclusion above still need further research and demonstration.