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Obesity (as defined by body mass index) has not been associated consistently with higher mortality in older adults. However, total body mass includes fat and muscle, which have different metabolic effects. This study was designed to test the hypothesis that greater muscle mass in older adults is associated with lower all-cause mortality.

All-cause mortality was analyzed by the year 2004 in 3659 participants from the National Health and Nutrition Examination Survey III who were aged 55 years or more (65 years if women) at the time of the survey (1988-1994). Individuals who were underweight or died in the first 2 years of follow-up were excluded to remove frail elders from the sample. Skeletal muscle mass was measured using bioelectrical impedance, and muscle mass index was defined as muscle mass divided by height squared. Modified Poisson regression and proportional hazards regression …