American Journal of Epidemiology Advance Access originally published online on August 24, 2005
American Journal of Epidemiology 2005 162(7):607-617; doi:10.1093/aje/kwi254
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ORIGINAL CONTRIBUTIONS |
Effects of Body Composition and Leisure-time Physical Activity on Transitions in Physical Functioning in the Elderly
1 Division of Epidemiology, School of Public Health, University of California, Berkeley, CA
2 Division of Research, Kaiser Permanente Medical Care Program, Oakland, CA
3 Department of Statistics, University of California, Berkeley, CA
4 Division of Biostatistics, School of Public Health, University of California, Berkeley, CA
Correspondence to Thaddeus J. Haight, Division of Epidemiology, School of Public Health, University of California, Berkeley, 140 Warren Hall, #7360, Berkeley, CA 94720-7360 (e-mail: tad{at}stat.berkeley.edu).
Physical activity and body composition were examined with respect to variation in functional limitation over a 6-year period (four surveys conducted between 1994 and 2000) based on a cohort of 1,655 community-dwelling older women and men living in Sonoma, California. Measures of functional limitation and physical activity were based on standard self-report questions. Measures of body composition (lean mass, fat mass) were estimated from bioelectric impedance by using population-specific prediction equations derived from dual-energy x-ray absorptiometry. For women, a one-unit gain in lean mass:fat mass ratio reduced the report of limitation at all surveys 65.5% (95% confidence interval: 21.8, 87.4). A similar reduction was not observed for men; however, there was a 3% increase in the report of no limitation at any survey. The effect of high levels of physical activity reduced new functional limitation that occurred at the last survey by 36.8% (95% confidence interval: 0.0, 92.2) for men and 52.7% (95% confidence interval: 13.5, 91.9) for women. In summary, higher levels of physical activity appeared to reduce the risk of future functional limitation conditional on the level of functioning established early in the disablement process by lean mass:fat mass ratio.
aging; body composition; causality; exercise; stochastic processes
Abbreviations: L/F, ratio of lean body mass to fat mass; LTPA, leisure-time physical activity; MET, metabolic equivalent; MSM, marginal structural model
Editor's note: An invited commentary on this article appears on page 618, and the authors' response is on page 621.
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