In a previous post, I reported on the results of a study that suggested that reducing TV viewing time by half can help overweight and obese individuals burn an additional 120 calories per day and lose some weight. A new study from Australia brings some more dramatic results: it suggests that increased sedentary activity, such as TV-viewing, is linked to increased risk of death due to cancer and cardiovascular disease, and that the findings appear to apply even to adults who have a healthy weight, not just obese ones.

Watching TV is one of several common behaviors that involve prolonged sitting. Recent studies from several developed countries such as the United States, the United Kingdom, and Australia suggest that aside from sleeping, watching TV is the behavior that occupies the most time while at home. Average television viewing time is around three hours per day in both Australia and the U.K. and is up to 8 hours in the U.S.!

In the new study, each additional hour of television viewing time was associated with an 11% increase in mortality from all causes and an 18% increased risk of cardiovascular disease-related mortality. Compared to those watching less than two hours of TV per day, those watching four or more hours of TV had a 46% increased risk of mortality from all causes and an 80% increased risk of cardiovascular disease-related mortality. These results were regardless of smoking status, blood pressure, cholesterol, diet, exercise, and current waist circumference.

It is not clear, however, how TV viewing actually affects mortality. While TV viewing is typically associated with increased snacking and less vigorous exercise, that does not seem to be the case in this study. Instead the authors suggest “that television viewing time significantly displaces light-intensity physical activity, which has been shown to be beneficially associated with cardiometabolic risk markers, including 2-hour postchallenge blood glucose.”

Just like the previous study, the message from this seems to be clear: it doesn’t matter what you do with your time, just don’t watch TV! As the study concludes: “Although continued emphasis on current public health guidelines on the importance of moderate- to vigorous-intensity exercise should remain, our findings suggest that reducing time spent watching television (and possibly other prolonged sedentary behaviors) may also be of benefit in preventing cardiovascular disease and premature death.”