A UK study has found that toddlers who spend more than two hours a day watching television double their risk of developing asthma before they become teenagers. Experts said more than television per se it is the fact that these children are leading a sedentary lifestyle that is the root cause.

Researchers tracked the health of 3,065, 3 ½ year old children who were asthma free and followed them for the next eight years. They were on the look out for wheezing or other tell-tale signs of asthma in the children.

The study funded by the U.K. Medical Research Council and published in the medical journal Thorax noted that by the age of 11 ½ about 185 or 6 % of the children had developed asthma. The children who watched more than 2 hours of television a day were seen to be twice as likely to be diagnosed with asthma as compared to those who spent less time viewing television although the odds were two in a 100.

They noted that the incidence of asthma rose with an increase in TV viewing time with the risk going up to 80% in the case of those who watched the most TV developing asthma by the time they were 12 as compared to those who watched less TV.

The researchers reported that of the children with asthma, 2% did not watch television, 20 % watched TV daily for less than an hour, while 34 % watched TV for 1 to 2 hours and 44 % watched more than 2 hours of TV everyday.

A. Sherriff, from the University of Glasgow’s dental school, and lead researcher of the study said, “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.”

The researchers added that as none of the children had any symptoms of asthma at the age of 3 ½ it was unlikely that the children exercised less due to asthma symptoms. As the study did not monitor the children’s exercise levels they base it on the assumption that children who watch more TV tend to be less active and that went on to predispose them to asthma.

Co-author Dr James Paton, from the University of Glasgow, said: "We think the problem is inactivity, not watching TV. TV is simply the best proxy marker for this. There may be a window in early in life when activity does something to protect the lungs. It may be that not sitting still makes you take deep breaths and that might be important in the long run."

Dr Elaine Vickers of Asthma UK said, "The findings add to a wealth of evidence linking a lack of exercise and being overweight with an increased risk of asthma, but this study is the first to directly link sedentary behaviour at a very young age to a higher risk of asthma later in childhood.

"We have one of the highest rates of childhood asthma in the world so it is especially important that parents in the UK try to prise their kids away from the TV and encourage them to lead an active lifestyle. This includes children with asthma, who can also greatly benefit from regular exercise."