The more time you spend watching TV, the greater your risk of dying at an earlier ageespecially from heart disease, researchers found.
The study followed 8,800 adults with no history of heart disease for more than six years. Compared to those who watched less than two hours of TV per day, people who watched four hours or more were 80% more likely to die from heart disease and 46% more likely to die from any cause. All told, 284 people died during the study.
Each additional hour spent in front of the TV increased the risk of dying from heart disease by 18% and the overall risk of death by 11%, according to the study, which was published today on the website of Circulation, an American Heart Association journal. (The study will appear in the Jan. 26 print edition.)
The pattern held even after the researchers took into account the education level and overall health of the participantstheir age, whether they smoked, and their cholesterol and blood pressure, for example.
Television isn't lethal in and of itself; the real problem appears to be that sitting is the "default position" for TV viewing, says lead study author David Dunstan, PhD, the head of the physical activity lab at the Baker IDI Heart and Diabetes Institute, a national research center in Victoria, Australia.
"Prolonged watching of television equals a lot of sitting, which invariably means there’s an absence of muscle movement," Dunstan says. If your muscles stay inactive for too long, it can disrupt your metabolism, he explains.
What's more, exercise doesn't necessarily make up for long sessions in front of the tube. Dunstan and his colleagues figured into their analysis how much the study participants exercised. When they compared groups of adults who exercised the same amount but watched varying amounts of TV, those who watched more TV were still at a higher risk of dying during the study.
“You can be active and also watch high amounts of television," Dunstan says. Television isn't necessarily replacing our exercise time, he explains, but it is replacing everyday, "non-sweaty" movements as basic as standing and walking from room to room. The positive health effects of these seemingly negligible activities are underestimated, he says.
Previous studies have reported a link between sitting time and the risk of heart disease and death, but this is the first to focus on television watching, which is one of the most common leisure activities. Adults in Australia, where the study was conducted, average about three hours a day; in the United States, the average has been estimated at up to five hours.