A Growth Factor Critical to Skeletal Muscle Mass

Recent research suggests low skeletal muscle mass is associated with increased endogenous insulin secretion, especially in patients aged older than 65 years.

Recent research indicates a link between skeletal muscle mass and insulin resistance in patients with type 2 diabetes mellitus (T2DM).

For example, one National Health and Nutrition Examination Survey (NHANES) found sarcopenia was strongly linked to adverse glucose metabolism among patients aged 60 years or older, including those who were not obese. Another study determined a 10% increase in skeletal muscle index (SMI) was associated with an 11% relative reduction in insulin resistance, which seemed to indicate that increased muscle mass is linked to decreased insulin resistance.

Even more recently, a research team from Osaka Medical College in Japan published a study in the January 2014 issue of Endocrinology Journal that examines the relationship between skeletal muscle mass and insulin secretion among patients with T2DM. As little research has been conducted in this area, the authors placed particular emphasis on the effect of sex and age on the relationship between sarcopenia and T2DM, which they characterized by both insulin resistance and beta-cell dysfunction.

For their study, the authors enrolled 138 T2DM patients who were consecutively treated at their institution. They measured skeletal muscle mass using bioelectrical impedance analysis and calculated SMI as the ratio of appendicular muscle mass (AMM) to total body weight. The researchers also collected fasting plasma glucose (FPG), glycosylated hemoglobin (HbA1c) data, and stimulated C-peptide immunoreactivity (CPR), which stimulates islet beta-cells directly and aggressively, and also evaluates insulin secretion and beta-cell function.

The authors found that AAM decreased as age increased, but SMI was unrelated to FPG or HbA1c levels. Among patients aged older than 65 years, SMI was negatively correlated with stimulated CPR values. Using multivariate analysis, the researchers identified a strong association between the log-transformed stimulated CPR value and SMI.

Although the study’s cross-sectional design did not determine disease duration or changes in skeletal muscle mass over time, the researchers said they are conducting a longitudinal follow-up study to explore those issues. In the meantime, their current findings suggest low skeletal muscle mass is associated with increased endogenous insulin secretion, especially in patients aged older than 65 years.