Purpose: Higher physical activity (PA) has been associated with greater attenuation of body fat gain and preservation of lean mass across the lifespan. These analyses aimed to determine relationships of change in PA to changes in fat and lean body mass in a longitudinal prospective study of postmenopausal women.
Methods: Among 11,491 women enrolled at three Women’s Health Initiative clinical centers who were selected to undergo dual-energy x-ray absorptiometry, 8352 had baseline body composition measurements, with at least one repeated measure at years 1, 3, and 6. PA data were obtained by self-report at baseline and 3 and 6 yr of follow-up. Time-varying PA effect on change in lean and fat mass during the 6-yr study period for age groups (50–59 yr, 60–69 yr, and 70–79 yr) was estimated using mixed effects linear regression.
Results: Baseline PA and body composition differed significantly among the three age groups. The association of change in fat mass from baseline and time-varying PA differed across the three age groups (P = 0.0006). In women age 50–59 yr, gain in fat mass from baseline was attenuated with higher levels of PA. Women age 70–79 yr lost fat mass at all PA levels. In contrast, change in lean mass from baseline and time-varying PA did not differ by age group (P = 0.1935).
Conclusions: The association between PA and change in fat mass varies by age group, with younger, but not older, women benefiting from higher levels of aerobic PA. Higher levels of aerobic activity are not associated with changes in lean mass, which tends to decrease in older women regardless of activity level. Greater attention to resistance training exercises may be needed to prevent lean mass loss as women age.
1Stanford Prevention Research Center, Department of Medicine, Stanford University, Stanford, CA; 2Quantitative Sciences Unit, Department of Medicine, Stanford University, Stanford, CA; 3University of Arizona Cancer Center, College of Medicine, University of Arizona, Tucson, AZ; 4Department of Epidemiology and Population Health, Albert Einstein College of Medicine, Bronx, NY; 5Division of Preventive Medicine, Brigham and Women’s Hospital, Harvard Medical School, Boston, MA; 6Department of Family and Preventive Medicine, University of California, San Diego, CA; 7Division of Nutritional Sciences, Cornell University, Ithaca, NY; 8Department of Epidemiology and Biostatistics, Drexel University School of Public Health, Philadelphia, PA; 9Division of Endocrinology and Metabolism, Department of Medicine, Georgetown University and Washington Hospital Center, Washington, DC; and 10Fred Hutchinson Cancer Research Center, University of Washington, Seattle, WA
Address for correspondence: Stacy T. Sims, Ph.D., Stanford Prevention Research Center, Medical School Office Building, 1265 Welch Road, Room X308, Stanford, CA 94305-5411; E-mail: email@example.com.
Submitted for publication May 2012.
Accepted for publication January 2013.