Working at a desk all day may not be as bad for heart health and longevity as sitting in front of a television after hours, according to a US study that suggests not all types of sitting are equally harmful.
"We've been hearing more and more about how sitting is the new smoking, and there is evidence to suggest that there are many adverse health risks associated with prolonged sedentary time," said Jeanette Garcia, a researcher at the University of Central Florida in Orlando who led the research.
"However, it's been unclear whether all sitting is created equal, suggesting that as long as you reduce any type of sitting, then that's helpful in improving health," Garcia said by email. "This study suggests that this may not be the case, and that we should focus more on leisure time sitting, mainly television viewing time, rather than sitting in general."
Almost one-third of the 3,592 African-American adults in the study watched television for more than four hours a day. Slightly more than one-third of them spent two to four hours daily sitting in front of the TV, while the remaining third watched TV for less than two hours a day.
People who spent more time in front of the television were more likely to be inactive, overweight, smokers, heavy drinkers, unhealthy eaters and to have an annual household income below $50,000 (S$67,645), researchers report in the Journal of the American Heart Association. They were also more likely to have high blood pressure and to lack a high school degree.
Researchers followed participants for an average of 8.4 years. During the study, 205 people died and 129 had events like heart attacks or strokes.
Compared to people who watched less than two hours of television daily, those who spent more than four hours in front of the TV were 49 per cent more likely to die or have a cardiovascular event.
But the negative health effects of television appeared limited to people who didn't get the recommended amount of weekly exercise for optimal health: 150 minutes of moderate to physical activity or 75 minutes of vigorous exercise.
There was also no meaningful difference in the chance of dying or having a heart attack or stroke based on how many hours people spent sitting at work.
People who reported spending more time sitting at work were more likely to be women, younger and overweight, but also to have high levels of leisure-time physical activity, to have graduated high school, to eat a healthy diet and to have a family income above $50,000. They were also less likely to be smokers or heavy drinkers, the researchers note.
It's possible that sitting in front of the TV might be worse than sitting at a desk because people snack while they're watching or stay up too late and don't get enough sleep, said Lin Yang, a researcher at the University of Calgary in Canada who wasn't involved in the study.
Lack of sleep or mindless snacking could both cause weight gain and contribute to other risk factors for heart disease that could make people more likely to die prematurely, Yang said by email.
"The evidence on TV viewing and health risks (is) strong, despite the biological mechanisms yet to be elucidated," Yang said.
The study wasn't designed to prove whether or how sitting might directly cause health problems, or if other factors shared by people who spend a long time sitting in front of the TV might be to blame.
It would be a mistake for people with desk jobs to assume there's no need to get moving during the work day, said Arch Mainous, a researcher at the University of Florida in Gainesville who wasn't involved in the study.
"Getting some activity at work needs to be integrated into the demands of the job," Mainous said by email.
"Take the stairs rather than the elevator, or take a walk at lunch," Mainous advised. "Leisure time physical activity is definitely beneficial but working in some more steps in the workday should also be encouraged."