June 6, 2011 (Denver, Colorado) — People with higher levels of sedentary behavior, such as prolonged watching television, have higher mortality rates than more active individuals — even when they participate in the recommended minimal levels of moderate physical activity, according to a study cosponsored by the National Cancer Institute and the American Association of Retired Persons (AARP), presented here at the American College of Sports Medicine 58th Annual Meeting.
The numerous health benefits of exercise are well known; however, less research has focused on lifestyles that are not entirely sedentary and instead combine some exercise along with higher levels of sedentary behavior, such as watching television.
The researchers therefore speculated that a sedentary lifestyle could have negative effects, even when people aren't entirely inactive.
"Sedentary behaviors are ubiquitous in modern life, but we don't fully understand the extent of adverse health effects associated with these behaviors, even after we account for the benefits of exercise or moderate to vigorous physical activity," said lead author Charles E. Matthews, PhD, a physical activity epidemiologist and investigator from the National Cancer Institute in Bethesda, Maryland.
Dr. Matthews and his team evaluated 240,819 adults 50 to 71 years of age who were involved in the National Institutes of Health–AARP Diet and Health Study. All subjects were free of cancer and cardiovascular and respiratory disease at baseline.
The amount of time the subjects spent sitting, watching television, and performing other activities was assessed by questionnaire at baseline, and mortality was evaluated over 8.5 years of follow-up.
The results indicated that, compared with people who reported viewing less than 1 hour per day of TV, participants who watched 7 or more hours a day of TV had a significantly greater risk for all-cause mortality (hazard ratio [HR], 1.61; 95% confidence interval [CI], 1.47 to 1.76), cardiovascular mortality (HR, 1.85; 95% CI, 1.56 to 2.20), and cancer mortality (HR, 1.22; 95% CI, 1.06 to 1.40).
Even when adults reported 4 to 7 hours a week of moderate to vigorous physical activity, daily television viewing of 5 to 6 hours was still associated with as much as a 50% increase in the risk for all-cause mortality (HR, 1.52; 1.30 to 1.79) and a 2-fold increase in risk for cardiovascular mortality (HR, 1.98; 1.41 to 2.77), compared with those reporting the most moderate to vigorous physical activity (7 hours or more per week) and the least television viewing (less than 1 hour per day).
The correlation remained after adjustment for age, sex, smoking, dietary intake, and race.
The findings suggest that the argument that even a small amount of exercise can somehow reduce mortality might not carry much weight, Dr. Matthews said.
"Previous studies have shown that engaging in moderate to vigorous activity, as little as 1 to 3 hours of exercise a week, is associated with substantial reductions in risk of early death."
"In contrast, our results indicate that while exercise did reduce risk of early death, even quite high levels of exercise (4 to 7 hours per week) did not overcome the influence of high levels of television viewing on mortality risk."
"The results add to the growing evidence that the adverse effects of sedentary behavior are independent of the benefits gained from moderate to vigorous activity," he said.
Although the study offers important insight into the potential role of sedentary behavior on mortality, more robust research should be conducted to address some unanswered questions, said Benjamin D. Levine, MD, director of the Institute for Exercise and Environmental Medicine at Texas Health Presbyterian Dallas, and distinguished professor in exercise science at the University of Texas Southwestern Medical Center at Dallas.
"I think the results are intriguing, although I am cautious about overinterpreting the data without knowing the resolution of the instruments used to assess physical activity and sitting behaviors," Dr. Levine said.
"Furthermore, these are just statistical associations, which in very large databases may be statistically significant, even though the biological significance can be questionable."
"It would be important to confirm these data with studies that use more robust tools to assess physical activity, such as activity monitors, which have become the gold standard in this field," Dr. Levine pointed out.
Dr. Matthews and Dr. Levine have disclosed no relevant financial relationships.
American College of Sports Medicine (ACSM) 58th Annual Meeting. Abstract 623. Presented June 2, 2011.
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