Toddlers who spend more than two hours a day watching television almost double their risk of getting asthma before they become teenagers, a study found.
Researchers identified 3,065 children without asthma when they were 31/2 and tracked them for the next eight years for wheezing or other telltale signs of the disorder that makes breathing difficult. Asthma rates rose in tandem with TV time, and those who watched the most had an 80 percent greater risk of being diagnosed by age 12 than those who watched less, according to the study in the medical journal Thorax.
The U.K. researchers used television viewing as a marker for sedentary behavior, since home computers and video-game systems weren't as widely used when the study began in the early 1990s. The results add asthma to a catalog of factors, including obesity, diabetes, smoking and promiscuity, tied to TV viewing.
"This study has shown for the first time a positive association between increased duration of reported TV viewing in early childhood and the development of asthma by 11.5 years of age in children with no symptoms of asthma in early childhood," said the researchers, led by A. Sherriff, from the University of Glasgow's dental school.
It's not clear exactly how sedentary behaviors like television watching are tied to asthma, the researchers said. There is some evidence to suggest exercise and deep breaths that come with it stretch the smooth muscles in the airways, while lack of exercise may make the lungs overly sensitive, they said.