Every two hours per day spent in front of the television boosted relative risk 20 percent for type 2 diabetes, 15 percent for cardiovascular disease, and 13 percent for all-cause mortality, Anders Grontved of the University of Southern Denmark in Odense and Dr. Frank B. Hu of Harvard School of Public Health found.
While it hasn't been shown that cutting back would prevent these problems among heavy viewers, Hu suggested that adults should limit themselves to the same threshold set for children by the American Academy of Pediatrics -- no more than two hours per day.
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"That's a very generous threshold," Hu said. "The amount of time spent watching TV is so high, if you can cut back to two hours that's a major improvement."
TV watching isn't just time taken away from less sedentary activities, but also is often time spent eating or snacking and watching commercials for unhealthy foods, Hu told MedPage Today.
It's an entire package that makes prolonged TV watching "an important and modifiable risk factor," Hu warned in the interview.
In the review of research known as a meta-analysis, for 100,000 individuals watching two hours per day over the course of one year:
176 would become diabetic
28 would die from cardiovascular disease
104 would die from any cause
The meta-analysis included eight studies reporting TV viewing habits of 175,938 adults and their incident outcomes.
The longer the time in front of the screen, the higher the risk the study subjects had for diabetes and cardiovascular disease. These risk of early death rose even more as TV watching rose above three hours per day. The findings also seemed to be independent of the weight of the individuals studied.
Although the meta-analysis included only adults, excess time in front of the screen has been found risky for children as well, Hu noted, pointing to studies showing increased obesity, a more unhealthy diet, and higher metabolic syndrome risk with longer daily TV viewing.
Young or not, "it's very important for physicians to ask their patients not only about their exercise habits, but also how much time they spend in front of the TV," he told MedPage Today.