Muscle Mass Linked to Risk for Insulin Resistance

Emma Hitt, PhD

August 04, 2011

August 4, 2011 — Building a higher muscle mass may improve insulin sensitivity and lower the risk for prediabetes or overt diabetes, findings of a new study suggest.

Preethi Srikanthan, MD, MS, with the Department of Medicine at the David Geffen School of Medicine at the University of California, Los Angeles, and colleagues reported the findings online July 21 in the Journal of Clinical Endocrinology & Metabolism.

"Our findings represent a departure from the usual focus of clinicians, and their patients, on just losing weight to improve metabolic health," noted Dr. Srikanthan in a press release. "Instead, this research suggests a role for maintaining fitness and building muscle," he said. "This is a welcome message for many overweight patients who experience difficulty in achieving weight loss, as any effort to get moving and keep fit should be seen as laudable and contributing to metabolic change."

The researchers used data from the Third National Health and Nutrition Examination Survey (NHANES III) conducted from 1988 through 1994 to determine whether increases in muscle mass at average and above-average levels are associated with improved glucose regulation.

A total of 13,644 participants were included in the analysis, which measured homeostasis model assessment of insulin resistance (HOMA-IR), blood glycosylated hemoglobin level, the prevalence of transitional/prediabetes or overt diabetes (PDM), and the prevalence of overt diabetes mellitus. They then related these measures to each person's skeletal muscle mass, which was estimated by bioelectrical impedance and divided that by total body weight to determine the skeletal muscle index (SMI).

The researchers found that each 10% increase in SMI was associated with an 11% relative reduction in HOMA-IR (95% confidence interval [CI], 6% - 15%) and a 12% relative reduction in PDM prevalence (95% CI, 1% - 21%).

Overall, increases in muscle mass above even average levels were associated with additional protection against insulin resistance and prediabetes. The finding is analogous to the relationship between social status and health, "where there is a continuous gradient between socio-economic status (SES)... and SES associations with health are not restricted to health differences between those living in poverty and everyone else," the study authors write.

According to the researchers, these findings underscore "the public health importance of monitoring muscle mass (relative to body size) in addition to body mass index and waist circumference in assessing an individual's metabolic health." They also suggest "a potential role for muscle-building exercises in preventing metabolic dysfunction."

"Further research is needed to determine the nature and duration of exercise interventions required to improve insulin sensitivity and glucose metabolism in at-risk individuals," Dr. Srikanthan stated.

The researchers also found that the link between muscle mass and diabetes was even stronger among people without diabetes vs those with diabetes, which may be related to the effect of diabetes on muscle tissue.

"It is known that the pathophysiology of DM [diabetes mellitus] causes atrophy of muscles, due to declines in the activity of anabolic hormones (e.g. IGF-1 [insulin-like growth factor 1], testosterone, ghrelin), increased inflammation, increased expression of acrogens that increase protein degradation, and the detrimental effects of DM on blood supply to muscle," they explain.

Independent commentator Wataru Aoi, PhD, with the Kyoto Prefectural University, in Kyoto, Japan, points out that these findings are important because it is well known that exercise improves insulin sensitivity, but it has not been demonstrated before that there is a relationship between skeletal muscle mass and insulin sensitivity.

"This study demonstrated that there is an inverse correlation," Dr. Aoi told Medscape Medical News. "The findings do suggest that patients at risk of diabetes should be counseled to perform exercise including resistance training," he said.

The study was not commercially funded. The study authors have disclosed no relevant financial relationships.

J Clin Endocrinol Metab. Published online July 21, 2011.

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