Sarcopenia: alternative definitions and associations with lower extremity function.

Objectives: To compare two sarcopenia definitions and examine the relationship between them and lower extremity function and other health related factors using data from the baseline examination of the Health Aging and Body Composition (Health ABC) Study.

Design: Observational cohort study.

Setting: Two U.S. communities in Memphis, Tennessee, and Pittsburgh, Pennsylvania.

Participants: Participants were aged 70 to 79 (N=2984, 52% women, 41% black).

Measurements: Participants were assessed using dual energy x-ray absorptiometry and were classified as sarcopenic using two different approaches to adjust lean mass for body size: appendicular lean mass divided by height-squared (aLM/ht2) and appendicular lean mass adjusted for height and body fat mass (residuals).

Results: These methods differed substantially in the classification of individuals as being sarcopenic, especially those who were more obese. The former method was highly correlated with body mass index and identified fewer overweight or obese individuals as sarcopenic. In both men and women, none of the obese group would be considered sarcopenic using the aLM/ht2 method, compared with 11.5% of men and 21.0% of women using the residuals method. In men, both classifications of sarcopenia were associated with smoking, poorer health, lower activity, and impaired lower extremity function. Fewer associations with health factors were noted in women, but the classification based on both height and fat mass was more strongly associated with lower extremity functional limitations (odds ratio (OR)=0.9, 95% confidence interval (CI)=0.7-1.2 for low kg/ht2; OR=1.9, 95% CI=1.4-2.5 for lean mass adjusted for height and fat mass).

Conclusion: These findings suggest that fat mass should be considered in estimating prevalence of sarcopenia in women and in overweight or obese individuals.