"Exercising at very light levels reduced deaths from any cause by 14 percent," said senior author Xifeng Wu, MD, PhD, professor and chair of the University of Texas MD Anderson Cancer Center Department of Epidemiology, in a news release. "The benefits of exercise appear to be significant even without reaching the recommended 150 minutes per week based on results of previous research."
The study cohort consisted of 416,175 persons in Taiwan (199,265 men and 216,910 women) who were evaluated between 1996 and 2008 in a standard medical screening program. Average duration of follow-up was 8.05 ± 4.21 years. Participants were categorized according to the amount of weekly exercise self-reported on a questionnaire as inactive, low, medium, high, or very high activity. For each group, life expectancy and hazard ratios (HRs) were calculated for mortality risk, with use of the inactive group as the standard.
The average amount of exercise in the low-volume activity group was 92 minutes per week (95% confidence interval [CI], 71 - 112) or 15 ± 18 minutes per day. Risk for all-cause mortality was 14% lower (HR, 0.86; 95% CI, 0.81 - 0.91), and life expectancy was 3 years longer in the low-volume activity group vs the inactive group.
Beyond the minimal amount of 15 minutes of daily exercise, each additional 15 minutes was associated with a further reduction in all-cause mortality risk by 4% (95% CI, 2.5 - 7.0) and in all-cancer mortality risk by 1% (95% CI, 0.3 - 4.5). These benefits of exercise were seen in all age groups, in both sexes, and in persons at risk for cardiovascular disease. Compared with individuals in the low-volume group, inactive persons had a 17% increased risk for mortality (HR, 1.17; 95% CI, 1.10 - 1.24).
"15 min a day or 90 min a week of moderate-intensity exercise might be of benefit, even for individuals at risk of cardiovascular disease," the study authors write.
Limitations of this study include observational design with possible confounding, reliance on self-report to determine exercise amount, lack of generalizability to other populations, and possible loss to follow-up.
In an accompanying editorial, Anil Nigam and Martin Juneau, from Montreal Heart Institute and Université de Montréal in Quebec, Canada, note that "this is the first observational study of this size to report important and global health benefits at such a low volume of leisure-time physical activity with this degree of precision."
"The knowledge that as little as 15 min per day of exercise on most days of the week can substantially reduce an individual's risk of dying could encourage many more individuals to incorporate a small amount of physical activity into their busy lives," Drs. Nigam and Juneau write. "Governments and health professionals both have major roles to play to spread this good news story and convince people of the importance of being at least minimally active."
The exercise project was funded by the Taiwan Department of Health Clinical Trial and Research Center of Excellence, and the Taiwan National Health Research Institutes supported this study. The study authors and editorialists have disclosed no relevant financial relationships.
Lancet. Published online August 16, 2011.
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