Decreased muscle mass may be a risk factor for type 2 diabetes
It is well known that controlling weight and reducing body fat is important in managing or even preventing type 2 diabetes. A new study also suggests that beyond these measures, increasing muscle mass may be equally important in maintaining stable and healthy blood glucose readings.
Researchers at the David Geffen School of Medicine at UCLA say that there is a correlation between greater muscle mass, relative to body size, and a substantially decreased risk of developing the metabolic changes that lead to diabetes. This may be welcome news to individuals who have a difficult time achieving lower weight goals. It turns out that the effort put into staying fit may be more protective than the ultimate number on the scale. That’s because exercise, especially weight-bearing exercise, boosts muscle mass. Muscle, in turn, is known as a far more efficient calorie burner than fat.
The discovery helps explain how overweight peasants living a traditional, active lifestyle wind up living healthy, long lives. My grandmother was one of them. Photos of her show a definitely rotund woman by the time she was in her early sixties. Yet she remained spry until her nineties. She was a woman on the constant move, hauling buckets of water from the family well, maintaining a large fruit and vegetable garden, feeding chickens, milking cows and, oh, yes, churning her own butter, which is one heck of a workout for those of you who have ever tried it by hand. No treadmill required.
In 2009, the UCLA researchers published a study suggesting that the ratio of waist size to hip size is a better predictor of premature death in older adults than either body mass index (BMI) or waist circumference alone. They then examined a condition called sarcopenic obesity, in which there is a low level of total body muscle mass (sarcopenia) combined with a high BMI (obesity). They theorized that the presence of this condition would correlate with higher insulin resistance and diabetes risk.
The following year, they tested this hypothesis by examining data from the National Health and Nutrition Examination Survey III (NHANES III); that data was culled from health information collected between 1988 and 1994 on 17,000 people aged 20 and older — an impressive sampling of people of various ages. They found that sarcopenia was indeed associated with increased insulin resistance in both non-obese and obese individuals, and also with higher levels of blood glucose in obese individuals.
For the current study, they again used NHAHES III data, this time on 13,644 adults who were not pregnant and had a BMI of at least 16.5, to see how this correlation applied to individuals representing the entire spectrum of muscle mass levels, rather than only those with sarcopenia. They wanted to determine if there was a correlation between higher levels of muscle mass and lower levels of insulin resistance, a precursor to diabetes.
After controlling for age, race and ethnicity, gender, generalized obesity (high BMI), and central obesity (large waist), they found that for each 10 percent increase in the skeletal muscle index (SMI) — the ratio of muscle mass to total body weight — there was a corresponding 11 percent reduction in insulin resistance and a 12 percent reduction in pre–diabetes, a condition characterized by higher-than-normal levels of glucose in the blood.
The American Diabetes Association estimates that 79 million Americans have pre-diabetes – an unsurprising number considering that one third of us are overweight and twice that many are sedentary. Presumably, a sedentary lifestyle leads to decreased muscle mass.
Extra fat is bad, but it appears that an increase in muscle mass may mitigate the negative impacts of the presence of fat.
Preethi Srikanthan, an assistant professor of medicine in the division of endocrinology and lead study author, points out that the study was not an intervention, it was observational. In other words, the authors did not look at the effect of different kinds of muscle-building activities on diabetes.
It's difficult to know when looking at a correlational study like this one whether it's just a correlation or an effect, says Duke endocrinologist Susan Spratt.
"Are there other healthy behaviors that tag along with high muscle mass that reduce the risk of diabetes? We don't know from this study that if you increase muscle mass you will decrease insulin resistance, but we can infer that might be the case," Spratt says.
The study was published online Thursday and in the September issue of the Journal of Clinical Endocrinology and Metabolism.