Abstract. Osteoporosis and type 2 diabetes mellitus (T2DM) are now prevalent in aging and westernized societies, and adversely affect the health of the elderly people by causing fractures and vascular complications, respectively. Recent experimental and clinical studies show that both disorders are etiologically related to each other through the actions of osteocalcin and adiponectin. Meta-analyses of multiple clinical studies show that hip fracture risk of T2DM patients is increased to 1.4 to 1.7-folds, although BMD of the patients is not diminished. Vertebral fracture risk of T2DM patients is also increased, and BMD is not useful for assessing its risk. These findings suggest that bone fragility in T2DM depends on bone quality deterioration rather than bone mass reduction. Thus, surrogate markers are needed to replace the insensitivity of BMD in assessing fracture risks of T2DM patients. Markers related to advanced glycation end products as well as insulinlike growth factor-I may be such candidates, because these substances were experimentally shown to modulate bone quality in DM. In practice, it is important for physicians to assess fracture risk in T2DM patients by evaluating prior VFs and fracture histories using spine X-ray and interview, respectively, until the usefulness of surrogate markers is established.
Key words: Type 2 diabetes mellitus, Bone fragility, Fracture risk, Osteocalcin, AdiponectinThe numbers of patients with osteoporosis or type 2 diabetes mellitus (T2DM) are increasing in aging and westernized societies. Both disorders predispose the elderly people to disabled conditions by causing fractures and vascular complications, respectively, which eventually raise their mortality. Although osteoporosis and T2DM are traditionally viewed as separate disease entities, accumulating evidence indicates that there are similar pathophysiological mechanisms underlying them.
I. Interaction between bone metabolism and glucose/fat metabolism through osteocalcin and Wnt signalingOsteocalcin (OC), one of the osteoblast-specific secreted proteins, has several hormonal features and is secreted in the general circulation from osteoblasts [1,2]. Recent animal studies have shown that OC action is related to not only bone metabolism but also glucose metabolism and fat mass [3,4]. Lee et al. showed that OC functions as a hormone that improves glucose metabolism and reduces fat mass, because OC-deficient mouse aggravated these processes [3]. Moreover, Ferron et al. showed that recombinant uncarboxylated OC administration to wild-type mice fed by high fat diet regulated gene expression in pancreatic ÎČ cells and adipocytes (including adiponectin expression), and prevented the development of metabolic diseases, obesity, and hyperglycemia [4]. Several clinical studies have also confirmed the relationship between OC and glucose/fat metabolism in humans [5][6][7][8][9]. We were the first to show that serum OC level was negatively correlated with plasma glucose level and atherosclerosis parameters in T2DM patients [5]. We ...