Children who watch television for more than two hours a day have twice the risk of developing asthma, British researchers reported Tuesday.
Asthma affects more than 300 million people worldwide and is the most common children's chronic illness. Symptoms include wheezing, shortness of breath, coughing and chest tightness.
A study published in the journal Thorax may help link asthma, estimated to account for one in 250 deaths globally each year, to obesity and lack of exercise, experts said.
"There has been a recent suggestion that breathing patterns associated with sedentary behavior could lead to developmental changes in the lungs and wheezing illnesses in children," Andrea Sherriff of the University of Glasgow and colleagues wrote.
Sherriff and colleagues studied more than 3,000 children from birth until nearly the age of 12.
The parents were questioned annually on wheezing symptoms among their children and whether a doctor had diagnosed asthma as they grew up. The researchers also analyzed how much television the children watched.
They did not consider video games or personal computers, which were not as common in the mid 1990s when the children were growing up, the researchers added.
The study found that 6 percent of children at around age 12 who had no symptoms of the disease growing up had asthma.
But children who watched television for more than two hours daily were almost twice as likely to have been diagnosed with the condition as those who watched less.
"The findings add to a wealth of evidence linking a lack of exercise and being overweight with an increased risk of asthma," Elaine Vickers of Asthma UK, who was not involved in the study, said in a statement.
"But this study is the first to directly link sedentary behavior at a very young age to a higher risk of asthma later in childhood."
In some countries as many as 30 percent of children develop the inflammatory disease, according to the World Health Association.