Bone disorders associated with diabetes mellitus and its treatments

Both type 1 and type 2 diabetes mellitus are associated with bone disorders, albeit via different mechanisms. Early studies in patients with type 1 diabetes suggested a 10-fold increase in the hip fracture risk compared to non-diabetic controls. Meta-analyses published more recently indicate a somewhat smaller risk increase, with odds ratios of 6 to 7. Diminished bone mineral density is among the contributors to the increased fracture risk. Both types of diabetes are associated with decreased bone strength related to low bone turnover. The multiple and interconnected pathophysiological mechanisms underlying the bone disorders seen in type 1 diabetes include insulin deficiency, accumulation of advanced glycation end products, bone microarchitecture alterations, changes in bone marrow fat content, low-grade inflammation, and osteocyte dysfunction. The bone alterations are less severe in type 2 diabetes. Odds ratios for hip fractures have ranged across studies from 1.2 to 1.7, and bone mineral density is higher than in non-diabetic controls. The odds ratio is about 1.2 for all bone fragility fractures combined. The pathophysiological mechanisms are complex, particularly as obesity is very common in patients with type 2 diabetes and is itself associated with an increased risk of fractures at specific sites (humerus, tibia, and ankle). The main mechanisms underlying the bone fragility are an increase in the risk of falls, sarcopenia, disorders of carbohydrate metabolism, vitamin D deficiency, and alterations in cortical bone microarchitecture and bone matrix. The medications used to treat both types of diabetes do not seem to play a major role. Nevertheless, thiazolidinediones and, to a lesser extent, sodium-glucose cotransporter inhibitors may have adverse effects on bone, whereas metformin may have beneficial effects. For the most part, the standard management of bone fragility applies to patients with diabetes. However, emphasis should be placed on preventing falls, which are particularly common in this population. Finally, there is some evidence to suggest that anti-fracture treatments are similarly effective in patients with and without diabetes.