By Maxine Frith
Chlorine in indoor swimming pools could be behind the massive increase in childhood asthma, recent British research reveals.
The study is worrying because children with asthma have been encouraged to swim, as it has been seen as a safe way to exercise without suffering breathing problems.
Researchers called for a move to non-chlorine based disinfectants and better air quality in swimming pools to reduce the risk.
One in seven children aged two to 15 in the UK suffers from asthma and the rate has risen sixfold in 25 years.
Scientists from the Catholic University of Louvain in Brussels studied more than 200 primary school children in Belgium who regularly swam in indoor pools. The results of the study into damage to the lung cells of children are published in the journal Occupational and Environmental Medicine. Destruction of the cellular barriers protecting the deep lung can make them "leaky" and more vulnerable to the allergens that cause asthma, the scientists say.
Children who swam regularly were more likely to have lung-cell damage, the researchers found. Those who swam most frequently had lung damage similar to that in regular smokers. Children who spent more time in swimming pools were also more likely to have asthma, and the association was strongest in the youngest age groups.
The scientists believe the damage is caused by a chemical generated when the chlorine comes into contact with organic matter such as sweat or urine. The by-product, nitrogen tricholoride, is easily inhaled in the hot atmosphere of indoor swimming pools.
Dr Alfred Barnard, the lead researcher, said: "The question needs to be raised as to whether it would not be prudent in the future to move towards non-chlorine based disinfectants, or at least to reinforce water and air quality control in indoor pools."
Professor Martyn Partridge, chief medical adviser to the National Asthma Campaign, said: "This is an interesting study and exposure of any child to a chemical which may damage the airways is clearly a matter of concern.
"But great care must be taken in interpreting these associations and it is unlikely that swimming, at least by itself, could really be the cause for the increase in asthma."
He said taking part in swimming might be another of the many Western lifestyle factors linked to an increased risk of asthma. "While we welcome research such as this, much more work needs to be done in this field before we can draw any conclusions and take action to turn off the epidemic of asthma," he said.