Relative Muscle Mass Is Inversely Associated with Insulin Resistance and Prediabetes. Findings from The Third National Health and Nutrition Examination Survey

CONTEXT: Insulin resistance, the basis of type 2 diabetes, is rapidly increasing in prevalence; very low muscle mass is a risk factor for insulin resistance. OBJECTIVE: The aim was to determine whether increases in muscle mass at average and above average levels are associated with improved glucose regulation. DESIGN: We conducted a cross-sectional analysis of National Health and Nutrition Examination Survey III data. PARTICIPANTS: Data from 13,644 subjects in a national study were evaluated. OUTCOME MEASUREMENTS: We measured homeostasis model assessment of insulin resistance (HOMA-IR), blood glycosylated hemoglobin level, prevalence of transitional/pre- or overt diabetes (PDM), and prevalence of overt diabetes mellitus. RESULTS: All four outcomes decreased from the lowest quartile to the highest quartile of skeletal muscle index (SMI), the ratio of total skeletal muscle mass (estimated by bioelectrical impedance) to total body weight. After adjusting for age, ethnicity, sex, and generalized and central obesity, each 10% increase in SMI was associated with 11% relative reduction in HOMA-IR (95% confidence interval, 6-15%) and 12% relative reduction in PDM prevalence (95% CI, 1-21%). In nondiabetics, SMI associations with HOMA-IR and PDM prevalence were stronger. CONCLUSIONS: Across the full range, higher muscle mass (relative to body size) is associated with better insulin sensitivity and lower risk of PDM. Further research is needed to examine the effect of appropriate exercise interventions designed to increase muscle mass on incidence of diabetes.