Although other sedentary activities also increased the risk of weight gain and diabetes, their impact was much smaller than the women's television viewing habits. For example, each additional two hours of sitting at work or driving a car was associated with a 5% increase in obesity and 7% increase in diabetes.
But the researchers found that even light activity can fight weight gain. The study showed that for each hour of brisk walking per day the women did, there was a 24% reduction in the risk of obesity and a 34% drop in diabetes risk.
Hu says those findings suggest that public health campaigns should not only promote increasing physical activity but they should also recommend a decrease in sedentary activities, like television watching.
"TV watching is the most prevalent and pervasive sedentary behavior in the U.S.," says Hu. "It's second only to the time we spend in bed."
Studies show the average American male spends an average of 29 hours per week watching television and the average American woman spends 34 hours per week watching television.
"There should be an upper limit for television watching. No more than 10 hours of TV watching per week, in addition to at least 30 minutes of walking per day," says Hu.
Researchers estimate that 30% of new obesity cases and 43% of new diabetes cases could be prevented by adopting that kind of relatively active lifestyle that limits television watching to less than 10 hours per week and incorporates moderate exercise, such as 30 minutes of brisk walking per day.
"We're not talking about running marathons, but just taking a walk around the park near your house can go a long way in reducing the risk of obesity and type 2 diabetes," says Hu.