People with desk jobs may not need to feel so guilty about all those sedentary hours in an office chair: Sitting at work may not be as bad for the heart as sitting in front of the TV, a new study suggests.

The study researchers analyzed information from more than 3,500 African American adults, and found that those who spent a lot of their leisure hours sitting in front of the TV were at higher risk for heart disease and death during the study period, compared with those who spent little time sitting in front of the TV.

But the same wasn't true for sitting at work: Study participants with sedentary jobs were at no higher risk for heart disease and death during the study period than those with more active jobs, according to the article, which was published today (July 26) in the Journal of the American Heart Association. [9 New Ways to Keep Your Heart Healthy]

Exactly why sitting in front of the TV would be worse than sitting at work isn't clear. But the time of day may play a role; watching TV often occurs around the time people eat dinner.

"The combination of eating a large meal such as dinner and then sitting for hours could also be particularly harmful," study senior author Keith Diaz, an assistant professor of behavioral medicine at Columbia University Vagelos College of Physicians and Surgeons in New York, said in a statement. The researchers plan to conduct more studies to examine why watching TV seems to be a particularly harmful form of sitting, and whether eating a large meal beforehand may be a contributing factor.

Risks of sitting

Numerous studies have found that spending too much time sitting is linked with a slew of health risks, including an increased risk of high blood pressure, type 2 diabetes and heart disease. But most of these studies looked at a single point in time, rather than following people over time, which limits the conclusions that can be drawn. (For instance, people who are in poorer health in the first place may spend more time sitting down.)

What's more, past studies rarely included diverse or minority populations, even though African Americans are at higher risk of heart disease in general, compared with other racial or ethnic groups in the U.S., the authors said.

In the new study, the researchers analyzed information from 3,592 African Americans living in Jackson, Mississippi, who were followed for about 8.5 years. All of the participants were employed.

Those who initially spent more than four hours a day sitting in front of the TV were subsequently 50% more likely to experience heart problems — such as a heart attack or diagnosis of heart disease — or to die during the study period, compared with individuals who initially watched less than two hours of TV a day.

In contrast, those who said they "often or always" sat at work were not more likely to experience heart problems or die during the study period, compared with those who said they "never or seldom" sat at work.

Moreover, it seems that the harmful effects of sitting in front of the TV could be offset by exercise. People who watched TV for four or more hours a day were not at increased risk for heart disease or death during the study period if they also engaged in adequate amounts of exercise, about 150 minutes per week.

Why is TV watching more harmful?

People may be more truly sedentary when they are watching TV compared with when they are at work, where they may be getting up to use the copier or visit a coworker. This could be another possible reason for the higher risks tied to TV-watching, the authors said. "It may be that most people tend to watch television for hours without moving, while most workers get up from their desk frequently," Diaz said.

In addition, it's possible that the increased cognitive demands of work versus those required for leisure time could also play a role. "Work place sitting is far more mentally active where we are using [our] brains to think creatively, problem solve, socialize, etc.," Diaz told Live Science in an email. "In comparison, TV viewing typically involves less mental functioning." The brain may also burn slightly more calories when it's mentally active, studies suggest.

The researchers note that the study was conducted in African Ameircan adults who were employed and living in a single area of the Southeastern U.S., and so it's unclear how well the findings would apply to other populations.

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