Scientists have confirmed that regular physical activity is associated with a lower risk of cardiovascular disease, dementia, all-cause disability and other health problems. However, few studies have looked at the possible association between time spent sitting and mortality. The two are not exact opposites, since a person who gets a good 30-minute work-out every day and then sits in front of a computer screen for 8 hours has high levels of both physical activity and sedentary behavior.
A new study by Emmanuel Stamatakis and colleagues at University College London has addressed the gap, and the results suggest that too much time spent in front of a computer or the TV increases the risk cardiovascular events and all-cause mortality, even in people also happen to engage in regular exercise.
To reach these troubling conclusions, Stamatakis’ group reviewed data from 4,500 respondents to the Scottish Health Survey of 2003. Participants were 35 years old or older, and were followed for at least 4 years.
Respondents were asked describe the time spent per day engaged in screen-based entertainment (like watching TV or surfing the Internet).
After adjusting for age, gender, BMI, ethnicity, social class, cigarette smoking and other factors, Stamatakis’ group determined that cardiovascular risk was about 50% higher among respondents who engaged in screen-based entertainment for two or more hours per day. They also found that all-cause mortality was more than twice as high among those who engaged in four or more hours of the same.
Importantly, when the scientists adjusted their analysis to account for physical activity, they found no appreciable reduction of the risk associated with sedentary behavior.
In an effort to study physiological mechanisms underlying the link between excessive sedentary behavior and cardiovascular risk, Stamatakis’ team looked at a subset of respondents for whom blood test results were available.
They found, rather surprisingly, that a combination of C-reactive protein (a non-specific measure of inflammation in the body), HDL (good) cholesterol and BMI explained only about 25% of the relationship.
“Further experimental studies will be required to determine the exact mechanisms accounting for increased cardiovascular disease risk during prolonged inactivity in humans,” Stamatakis’ team concluded.
The scientists’ findings are consistent with the few earlier studies that have addressed the matter, including this one.
