Hitting the gym every day might do little to decrease your risk of death if you spend the rest of your time sitting down, a new study suggests.
The results show the time people spend on their derrieres is associated with an increased risk of mortality, regardless of their physical activity level.
The findings suggest public health messages should promote both physical activity and less time on the couch, the researchers say.
The current obesity epidemic in the United States has been attributed in part to reduced overall physical activity.
While several studies support a link between sitting time and obesity, type 2 diabetes, risk factors for cardiovascular disease risk and unhealthy dietary patterns in childrenand adults, very few studies have examined time spent sitting in relation to total mortality. Thus, public health guidelines focus largely on increasing physical activity with little or no reference to butt-on-the-chair time.
Alpa Patel, a researcher at the American Cancer Society (ACS), and his colleagues analyzed survey responses from 123,216 individuals (53,440 men and 69,776 women) who had no history of cancer, heart attack, strokeor emphysema that were enrolled in the ACS's Cancer Prevention II study in 1992. Participants were followed from 1993 to 2006.
The researchers examined the participants' amount of time spent sitting and physical activity in relation to mortality over the 13-year period.
Women more affected by sitting
More leisure time spent sitting was associated with higher risk of mortality, particularly in women.
Women who reported more than six hours per day of sitting (outside of work) were 37 percent more likely to die during the time period studied than those who sat fewer than three hours a day. Men who sat more than six hours a day (also outside of work) were 18 percent more likely to die than those who sat fewer than three hours per day. The association remained virtually unchanged after adjusting for physical activity level. Associations were stronger for cardiovascular disease mortality than for cancer mortality.
When combined with a lack of physical activity, the association was even stronger. Women and men who both sat more and were less physically active were 94 percent and 48 percent more likely to die during the study period, respectively, compared with those who reported sitting the least and being most active.
"Several factors could explain the positive association between time spent sitting and higher all-cause death rates," Patel said. "Prolonged time spent sitting, independent of physical activity, has been shown to have important metabolic consequences, and may influence things like triglycerides, high density lipoprotein, cholesterol, fasting plasma glucose, resting blood pressure, and leptin, which are biomarkers of obesity and cardiovascular and other chronic diseases."
(High density lipoprotein is considered the "good" kind of cholesterol.)
The results are published in an early online edition of the American Journal of Epidemiology.