March 3 (HealthDay News) -- Children who watch TV for more than two hours a day or are otherwise inactive have a doubled risk for asthma, according to a U.K. study.

Researchers looked at more than 3,000 children whose respiratory health was monitored from birth to 11.5 years of age.

Each year, parents were asked about any symptoms of wheezing in their children and whether their children had been diagnosed with asthma by the time they were 7.5 years old, but not before they were 3.5 years old.

The parents were also asked to report on their children's TV viewing habits after the age of 3.5 years. The amount of time spent in front of the TV was used a measure of sedentary behavior.

By the time the children were 11.5 years old, the overall asthma rate among those who had no asthma symptoms when they were 3.5 years old was 6 percent. However, those who watched TV for more than two hours a day were almost twice as likely to have asthma as those who watched less TV.

The results weren't confined to one gender and weren't related to the children's current weight.

The study was published online and was expected to be in an upcoming print issue of the journal Thorax.

The link between physical activity, sedentary behavior and asthma is complex, noted Dr. Andrea Sherriff, of the University of Glasgow, and colleagues. They noted that previous research suggests breathing patterns in children may be associated with sedentary behavior, triggering developmental changes in the lungs and subsequent wheezing.

SOURCE: BMJ specialist journals, news release, March 3, 2009