The association between physical activity and reduced body fat lessens with age - results from a cross-sectional study in community-dwelling older adults

Introduction: The aim of this study was to describe the relationship between accelerometer-determined physical activity (PA) and adiposity in community-dwelling older adults. In addition, we were interested in comparing the extent of correlation between questionnaire and accelerometer determined PA.

Methods: 636 community-dwelling older adults (66±7years) were studied. Adiposity was measured using dual-energy X-ray absorptiometry and BMI was calculated. We measured minutes/day spent in sedentary, light, moderate and vigorous intensity activity using both questionnaires and Actigraph GT1M accelerometers.

Results: Participants spent a median of 583(IQR 522-646), 225(176-271), 27(12-45) and 0(0-0) minutes in sedentary, light, moderate and vigorous activities respectively. There was a non linear dose-response inverse relationship between activity intensity and adiposity. After adjusting for age, sex and other levels of PA, for every 10minute increase in activity, total body fat decreased by 169g(95% CI 61-277), 905g(632-1178), and 2208g(759-3657) for light, moderate and vigorous activities respectively. There was an interaction between age and activity; as age increased, the magnitude of the effects of light and moderate activities on adiposity decreased. Sedentary minutes were not associated with adiposity after adjusting for time spent at other PA intensities. Questionnaire measures of PA were weakly correlated with body fat measures when compared to accelerometer determined PA.

Conclusion: Both the amount and intensity of PA, but not sedentary time, have an independent dose-response association with adiposity. The association is much stronger using objective assessment compared to questionnaire. The magnitude of these associations decrease with age suggesting that physical activity programmes may need to be modified with increasing age.