If your daytime or evening routine revolves around watching television, the results of a new study may prompt you to rethink how you spend some of your leisure time.

As reported in the Journal of the American Medical Association, Harvard researchers assessed the television viewing habits of more than 50,000 participants of the long-running Nurses' Health Study. They also tallied how much time the women routinely spent standing or walking either at home or at work. The researchers then kept track of the women over the following 6 years, noting how many became obese or developed type 2 diabetes during that time.

Consequence of a sedentary lifestyle

The results showed that women who watched more than 20 hours of television a week were over 60% more likely to become obese than those who watched little TV. These women were also more likely to develop type 2 diabetes, a disease that goes hand-in-hand with obesity in middle-aged and older adults.

In contrast, the women who spent more than 20 hours each week standing or walking around at home - either doing housework or walking for exercise - were less likely than other participants to be obese by the end of the study.

TV is only part of the picture

It's obvious that television viewing itself doesn't make people overweight, but it is associated with unhealthy habits that can contribute to weight gain. Television viewing requires little energy, yet the pervasive advertisements it carries for high-fat and high-sugar foods and beverages encourage snacking.

The authors also note that the women who watched the most TV were more likely to smoke and drink alcohol and less likely to exercise, when compared with others in the study. They also tended to eat more snacks and sweets and fewer fruits, vegetables and whole grain foods - all habits that make it harder to control weight.

Making physical activity a priority

Only 15% of the women in this study belong to what the authors termed the 'low risk group' - those who watched less than 10 hours of television a week and who exercised more than 30 minutes a day. The authors estimate that if everyone was able to meet those minimum goals, the number of cases of obesity in the US would be cut by 30% and cases of type 2 diabetes would decrease by more than 40%.

This study underscores the message that health professionals have been trying to communicate for some time: any amount of physical activity is better than none at all, and the type of activities that benefited the women in this study - working around the house and walking - are reasonable exercise options for most adults.