Children who watch more than five hours of television a day are at an increased risk of developing asthma, scientists have found.
Researchers concluded that the danger of them developing the respiratory condition was raised by more than half compared with children who watch just one hour.
This could be attributed to the fact that children who lead a "couch potato" lifestyle sigh much less than their healthier counterparts. Deep inspirations play a significant role in helping lungs to function but sitting for hours leads to shallow breathing.
Dr Giuseppe Corbo, who led the research carried out by the Catholic University, Rome, said: "Prolonged sitting is associated with a decrease in spontaneous sighs, which regulate airways."
The study of 20,000 six and seven-year-olds, published in the medical journal Epidemiology, confirmed a strong link with asthma and obesity, but found that salt was the biggest risk. Those with the highest intake were two and a half times more likely to develop asthma.
Children who played more computer games and watched more television were also found to be less active and had poorer diets.
The British Lung Foundation said: "Obesity, high TV viewing and a high salt diet get children off to a bad start in life."
More than a million children in Britain have asthma.