CYP27A1 and diabetes mellitus: As shown in Table 5, compared with the primary fracture group: serum CTX levels were lower in the re-fracture group with combined diabetes (P < 0.05); L1-4 BMD, femoral neck BMD, and total hip BMD levels were lower in the re-fracture group with combined cardio-cerebrovascular diseases (P < 0.05); femoral neck BMD and total hip BMD levels were lower in the re-fracture group with combined chronic gastric diseases (P < 0.05) The rest of the bone metabolic markers were not statistically different between the groups (P > 0.05).