Originally published in MedPage Today
by Todd Neale, MedPage Today Staff Writer
Too much television watching could be shortening lifespans, a study of Australian adults showed.
Aussies who reported watching four or more hours of TV a day were 46% more likely to die during a 6.6-year period than those who watched less than two hours a day, according to David Dunstan, PhD, of Monash University in Melbourne, and colleagues.
The risk of dying from cardiovascular disease during follow-up was 80% greater in the excessive viewers, although statistically, the result attained only borderline significance (P=0.05), the researchers reported online in Circulation: Journal of the American Heart Association.
The associations were independent of leisure-time exercise and traditional risk factors such as smoking, poor diet, high blood pressure, and abdominal obesity.
“Sedentary living provokes coronary artery disease,” commented Gerald Fletcher, MD, a cardiologist at the Mayo Clinic in Jacksonville, Fla., and spokesman for the American Heart Association who 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 the relationship between mortality risk and television viewing — the predominant leisure-time sedentary activity — had not been studied, Dunstan and colleagues wrote.
To explore the issue, they turned to the Australian Diabetes, Obesity, and Lifestyle Study (AusDiab).
Excluding those with 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 increased risks of all-cause death (HR 1.11, 95% CI 1.03 to 1.20) and death from cardiovascular disease (HR 1.18, 95% CI 1.02 to 1.35).
Further adjustment for other factors related to mortality risk eliminated the association between TV watching and cardiovascular death but not with all-cause mortality (HR 1.08, 95% CI 1.00 to 1.17, P=0.048).
In fully adjusted models, watching four or more hours of TV a day was associated with greater risk of all-cause mortality and cardiovascular death compared with watching less than two hours.
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 cardiometabolic 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 says, ‘Gosh, that means something and maybe I should stop that,’ but the other nine don’t,” he commented.
The researchers listed some limitations of the study:
* Researchers assessed a single sedentary behavior.
* TV time was self-reported and evaluated at baseline only.
* Residual confounding may have existed.
* Reverse causality, in which diagnosed or undiagnosed illness at the beginning of the study may have resulted in elevated TV watching time, could not be excluded.