Using data from the Peking Vertebral Fracture Study, we conducted a longitudinal cohort study to investigate the association between type 2 diabetes mellitus (T2DM) and the risk of incident fractures, especially of vertebral fractures (VFs), and we also examined the modifying effect of body mass index (BMI) on this association and the effect of bone mineral density (BMD) T-score as a risk factor for incident fractures in T2DM. Chinese postmenopausal women were enrolled (n = 982), among whom 186 had T2DM. Incident VFs were confirmed by lateral radiographs of the thoracolumbar spine (T4-L5), while incident clinical non-VFs were self-reported. BMDs at the lumbar spine (LS) and femoral neck (FN) were measured by dual-energy X-ray absorptiometry. T2DM and non-DM women were at similar risk for VFs (OR 0.74, 95% CI 0.32-1.74), even adjusting for age, BMI, BMD, and previous fractures. Meanwhile, T2DM women had nearly twice the risk for non-VFs (HR 1.95, 95% CI 1.11-3.35) compared with non-DM women. After stratifying by BMI, the risk of VFs remained similar between diabetics and non-diabetics despite their BMI status (p for interaction = 0.470), and the risk of non-VFs was positively associated with T2DM only in women with BMI ≥ 25 kg/m2 (HR 3.59, 95% CI 1.68-7.65) (p for interaction = 0.065). Although LS BMD T-score was similarly and negatively associated with incident VFs both in T2DM (OR 0.34, 95% CI 0.12-0.88) and non-DM women (OR 0.60, 95% CI 0.44-0.82) (p for interaction = 0.430), the FN BMD T-score was not found to be significantly associated with either non-VFs or VFs among T2DM women. Comparing T2DM and non-DM women with similar fracture risks, the mean difference in LS T-score was - 0.36 (95% CI - 1.77 to 1.04) for VF, and difference in FN T-score was 1.61 (95% CI - 0.11 to 3.34) for non-VF. In conclusion, Chinese postmenopausal women with T2DM had a similar risk of incident VFs, but a significantly higher risk of incident non-VF, compared to women without DM. Higher BMI did not modify the effect of T2DM on risk of VFs, but it increased the association between T2DM and risk of non-VFs. LS BMD T-score was similarly and negatively associated with VF risk in T2DM and non-DM women and appear to be useful for clinical evaluation of VF risk.
Keywords: Body mass index; Bone mineral density; Peking vertebral fracture stud; Type 2 diabetes mellitus; Vertebral fractures.