Hoai-Tran Bui

USATODAY

Watching television isn't just slowly killing your brain cells, it may be slowly killing you. Researchers found that people who watched three or more hours of television a day were at twice the risk of an early death than those who watched less.

A new report published in the Journal of the American Heart Association studied more than 13,000 Spanish university graduates for about eight years to determine the association between sedentary behaviors and risk of death. The study focused on television viewing time, time spent on the computer and time spent driving.

"Television viewing is a major sedentary behavior, and there is an increasing trend toward all types of sedentary behaviors," said Miguel Martinez-Gonzalez, the study's lead author and professor at the University of Navarra in Pamplona, Spain.

Over the course of the study, there were 97 deaths, 19 from cardiovascular causes, 46 from cancer and 32 from other causes. The study found a correlation to television watching time but found no significant association with computer or driving time.

"Watching television is a passive, sedentary activity, and certainly people who do it for hours are not paying attention in terms of their lifestyle and in terms of their diet," said American Heart Association cardiologist Nisa Goldberg.

A sedentary lifestyle is often associated with diabetes or heart disease, Goldberg said. When a person is sedentary for too long, the blood vessels can stiffen and cause a buildup of cholesterol in the arteries, she said. These are the building blocks of heart disease, Goldberg said.

Martinez-Gonzalez's study builds on other studies about "sitting disease," which found that sitting for more than six hours a day can be a risk factor for early death. Previous research suggests that half of U.S. adults are leading sedentary lives, the study said.

The television-watching study was started about 15 years ago and did not take into account new television-watching habits or smartphone use. Martinez-Gonzalez said that if he were to do this study now, he would ask participants to differentiate between using computers for work and entertainment. Martinez-Gonzalez said this is an important distinction, because when using computers or driving, the brain is more active.

"When you're watching television, you're completely relaxed, spending no energy, and there's no tension in your muscles," Martinez-Gonzalez said. "If you're driving or using a computer for working, you are stressed."

Martinez-Gonzalez said people who frequently watch television for three or more hours a day tend to be more isolated and less likely to engage in physical activities outside of their home.

"They are alone, and to be lonely is a risk factor for death," Martinez-Gonzalez said.

No one knows why there's a difference between watching television and other activities, Goldberg said, and more studies need to be done to understand why television behavior increases the risk of premature death. Martinez-Gonzalez wants to follow up with the participants and try to home in on the reasons for high rates of premature death.

"Our findings suggest adults may consider increasing their physical activity, avoid long sedentary periods and reduce television watching to no longer than one to two hours each day," Martinez-Gonzalez said.