Most are aware that regular exercise benefits health and that excess pounds do the opposite. Now, a new UCLA study has found that the more muscle mass Americans seniors have, the less likely they are to die prematurely. The study authors note that their findings add to the growing evidence that overall body composition, rather than the widely used body mass index (BMI), is a better predictor of all-cause mortality. They published their findings on February in the American Journal of Medicine.
Lead researcher Dr. Preethi Srikanthan, an assistant clinical professor in the endocrinology division at the David Geffen School of Medicine at UCLA, explained, “As there is no gold-standard measure of body composition, several studies have addressed this question using different measurement techniques and have obtained different results. 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.”
The investigators accessed data from the National Health and Nutrition Examination Survey (NHANES) III, which was conducted between 1988 and 1994. They concentrated on a group of 3,659 individuals, which included men who were 55 or older and women who were 65 or older at the time of the survey. The study was a cohort study, meaning it was composed of individuals with similar characteristics; in this case, seniors. The researchers then determined how many of those individuals had died from natural causes based on a follow-up survey done in 2004. The subjects’ body composition was measured using bioelectrical impedance, which involves passing an electrical current through the body. The current passes more readily through muscle than it does through fat; this is due to the water content of muscle. This procedure allowed the researchers to determine a muscle mass index: the amount of muscle relative to height; this index was similar to a body mass index. They then assessed how this muscle mass index related to the risk of death. They found that all-cause mortality was significantly lower in the fourth quartile (25%) of muscle mass index compared with the first quartile.
“In other words, the greater your muscle mass, the lower your risk of death,” explained co-author Dr. Arun Karlamangla, an associate professor in the geriatrics division at the medical school. He added, “Thus, rather than worrying about weight or body mass index, we should be trying to maximize and maintain muscle mass.”
The authors noted that their study has some limitations. Investigators cannot definitively establish a cause-and-effect relationship between muscle mass and survival using a cohort study such as NHANES III. However, Dr. Srikanthan explained that muscle mass appears to be an important predictor of risk of death. Furthermore, bioelectrical impedance is not the most advanced measurement technique. However, the NHANES III measurements were conducted in a very rigorous manner; thus, it offered the best possible situation for a study of this size.