Elevated vitamin D status in postmenopausal women on thiazolidinediones for type 2 diabetes

Thiazolidenediones (TZD) have been reported to lead to non-vertebral bone loss in postmenopausal women with diabetes, but the true incidence of vertebral fractures has been under-detected because two-thirds of vertebral fractures are silent. TZD is also related to increased adiposity, with a consequently greater risk of vitamin D deficiency—both of which seem to aggravate the untoward effect of TZD on bone. The aim of this study is to determine whether TZD use is associated with prevalence of vertebral fractures and low vitamin D status in postmenopausal women with type 2 diabetes. A group of 102 postmenopausal women with type 2 diabetes, 52 TZD users for at least 12 months, and 50 non-TZD users were enrolled in the study. Any data regarding diabetes, age at menopause, co-morbidities, and drug use were recorded. Blood sampling and thoraco-lumbar radiography were performed. Bone mineral density (BMD) of L2–L4 and the femur were measured by dual-energy X-ray absorptiometry (DXA). The occurrence of vertebral fractures at one level or more in subjects on TZD was higher than those not on TZD, but did not reach statistical significance (19.2 vs. 14.0%, P = 0.5). Total hip BMD in subjects on TZD was significantly lower than those not on TZD (0.96 ± 0.15 vs. 1.02 ± 0.11; P < 0.05). Levels of 25(OH)D in TZD users were significantly higher (35.3 ± 1.5 vs. 25.9 ± 1.2 ng/dl; P < 0.001). The prevalence of vitamin D deficiency was 75.5% in subjects not on TZD compared to 34.6% in those on TZD (OR 6.4, 95% CI 2.6–15.6). Higher circulating 25(OH)D was observed in TZD users. TZD use was associated with lower total hip BMD but not with vertebral fracture.