Insulin resistance, bone health, and fracture risk

Insulin resistance, defined as an impaired biological response to insulin stimulation in target tissues, arises most frequently in the presence of central obesity. Although obesity is generally associated with increased bone mass, recent data challenge this view and, if complicated by T2DM, obese patients are at high risk for fragility fractures. IR may play a key role in this increased fracture risk through effects on bone quality rather than bone quantity. Further understanding of the mechanisms and approaches to prevent osteoporotic fractures in IR-related diseases is needed.

The dramatic increase in obesity and metabolic syndrome (MetS) over the last half-century has led to a worldwide epidemic of type 2 diabetes mellitus (T2DM) as well as in the incidence of insulin resistance (IR). IR is defined as an impaired biological response to insulin stimulation in target tissues and is primarily related to the liver, muscle, and adipose tissue. The most frequent underlying cause is central obesity, and it is known that excess abdominal adipose tissue secretes increased amounts of free fatty acids, which directly affects insulin signalling, reduces glucose uptake in muscle, and triggers excessive triglyceride synthesis and gluconeogenesis in the liver. When pancreatic β cells are unable to secrete the higher levels of insulin needed, T2DM, the main complication of IR, occurs.

Although obesity is generally associated with increased bone mass, recent data challenge this view and highlight the multifaceted nature of the obesity-bone relationship. Patients with T2DM are at significant risk for well-known complications of diabetes, including retinopathy, nephropathy, macrovascular disease, and neuropathy, but it is clear that they are also at high risk for fragility fractures. Moreover, recent data provide strong evidence that IR may key role in the increased fracture risk observed in both obesity and T2DM.

In this concise review article, the role of IR in increased risk of osteoporotic fractures in MetS, obesity, and T2DM is discussed and summarised, including consideration of the need for fracture risk assessment as a 'preventive measure', especially in patients with T2DM and chronic MetS with abdominal obesity. Personalised and targeted diagnostic and therapeutic approaches to prevent osteoporotic fractures in IR-related diseases are needed and could make significant contributions to health outcomes.