Jan. 12, 2009— -- Too much TV watching could mean a shorter lifespan, an Australian study has found.
Aussies who reported watching four or more hours of TV a day were 46 percent more likely to die during a 6-and-a-half-year period than those who watched less than two hours a day, according to David Dunstan of Monash University in Melbourne and colleagues.
The risk of dying from cardiovascular disease during follow-up was 80 percent greater in the excessive viewers -- although, statistically, the association was only slightly stronger than what could be chalked up to chance -- the researchers reported online in Circulation: Journal of the American Heart Association.
But the associations were seen even when leisure-time exercise and traditional risk factors such as smoking, poor diet, high blood pressure, and abdominal obesity were taken into account.
"Sedentary living provokes coronary artery disease," commented Dr. Gerald Fletcher, a cardiologist at the Mayo Clinic in Jacksonville, Fla. and spokesman for the American Heart Association. Fletcher was not involved in the study.
"Even if you exercise, if you have a lot of sedentary living with the things that go along with it -- the bad diet and everything else -- you still have a net degree of physical inactivity, which is a coronary artery disease risk factor," Fletcher told MedPage Today.
Previous studies had linked increased sedentary time, in general, to cardiovascular events and mortality risk. But but the relationship between mortality risk and television viewing -- the predominant lesiure-time sedentary activity -- had not been studied, Dunstan and his colleagues wrote.
To explore the issue, they turned to the Austalian Diabetes, Obesity, and Lifestyle Study.
Excluding those who already had a history of cardiovascular disease, the researchers asked 8,800 adults living throughout Australia about the amount of time they spent watching TV and followed them for an average of 6.6 years.
During follow-up, there were 284 deaths -- 87 from cardiovascular disease, 125 from cancer, and 72 from other causes.
After adjustment for age, sex, waist circumference, and exercise, each additional hour of television time per day was associated with an 11 percent increased risk of early death from any cause and an 18 percent increased risk of death from heart disease. TV watching was not significantly related to death from cancer or other causes.
According to Dunstan and his colleagues, the mechanism underlying the link between sitting and heart disease and metabolic disease risks is unclear.
"Observational studies with objective measures of sedentary time have reported significant associations of total sedentary time with blood glucose, blood lipids, and adiposity that are independent of moderate to vigorous exercise," they noted.
In addition, "animal studies have found enforced sedentary time to be related to lipoprotein lipase activity," they wrote.
"Our findings broadly support these hypothesized physiological links."
Mayo's Fletcher said studies like this might serve as a wake-up call for some patients, but he was not optimistic.
"Sometimes one out of 10 people say, 'Gosh, that means something and maybe I should stop that,' but the other nine don't," he commented.