Objectives To compare the effects of four different amounts of exercise for preventing depressive symptoms in community-dwelling older adults. Design Prospective cohort study. Setting A nationally representative sample in Taiwan. Participants Four waves of the survey 'Taiwan Longitudinal Study on Aging (TLSA)' from 1996 to 2007 were analysed. A total of 2673 older adults aged 65 years and over were recruited. Primary and secondary outcome measures Depressive symptoms were measured using the Center for Epidemiologic Studies Depression Scale (CESD). Four different types/amounts of exercise were examined including: (1) 3 times/week, 15 min/time; (2) 3 times/week, 30 min/time; (3) 6 times/week, 15 min/time; and (4) 6 times/week, 30 min/time. All exercise types were required to have at least moderate intensity. The impacts of different amounts of exercise on depressive symptoms were analysed using generalised linear mixed models. Results More than one-fifth of the elder individuals under consideration had depressive symptoms (CESD ≥10). About 38.6% of older adults met the lowest criteria for exercise type 1, and fewer (28.0%) met the highest criteria for type 4. Only exercise type 4 in the current survey was initially related to lower depressive symptoms (OR=0.8, 95% CI 0.66 to 0.95). However, after considering the interaction between time and changes in exercise patterns, the results showed that all persistent exercise models, even if a very low amount (3 times/week, 15 min/time), had significantly preventive effects on depressive symptoms (OR=0.56∼0.67). Conclusion Consistent exercise with at least 15 min per time, three times a week of moderate intensity is significantly associated with lower risk of depressive symptoms. This low amount of exercise may be easier to promote at the community and population level than other alternatives. Trial registration Registry number 104040 of the Institutional Ethics Committee of Chia-Yi Christian Hospital.
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