PhotoWant to live a long time? Get into the gym and start pumping iron. Boiled down to its essence, that's the takeaway message from new UCLA research. It suggests that the more muscle mass older Americans have, the less likely they are to die prematurely.

The findings add to the growing evidence that overall body composition — and not the widely used body mass index, or BMI — is a better predictor of all-cause mortality.

"So many studies on the mortality impact of obesity focus on BMI. Our study indicates that clinicians need to be focusing on ways to improve body composition, rather than on BMI alone, when counseling older adults on preventative health behaviors," said Dr. Preethi Srikanthan, an assistant clinical professor at UCLA. The study, published in the American Journal of Medicine, is the culmination of previous UCLA research led by Dr. Srikanthan.

The researchers analyzed data ona group of 3,659 individuals that included men who were 55 or older and women who were 65 or older at the time of the survey. The authors then determined how many of those individuals had died from natural causes based on a follow-up survey done in 2004.

Muscle mass index

The body composition of the study subjects was measured using bioelectrical impedance, which involves running an electrical current through the body. Muscle allows the current to pass more easily than fat does, due to muscle's water content. In this way, the researchers could determine a "muscle mass index" — the amount of muscle relative to height — similar to a body mass index. They looked at how this muscle mass index was related to the risk of death.

They found that all-cause mortality was significantly lower in the fourth quartile of muscle mass index compared with the first quartile.

"In other words, the greater your muscle mass, the lower your risk of death," said Dr. Arun Karlamangla, the study's co-author. "Thus, rather than worrying about weight or body mass index, we should be trying to maximize and maintain muscle mass."

"Future research should determine the type and duration of exercise interventions that improve muscle mass and potentially increase survival in (healthy), older adults," the researchers wrote.

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