Children who use chlorinated open-air swimming pools have an increased risk of developing asthma, research presented at the European Respiratory Society (ERS) congress in Stockholm has found.
While it is known that chlorinated indoor swimming pools are linked to increasing levels of asthma, a study of children by researchers from the Catholic University of Louvain in Belgium has shown that regular users of open-air pools are also at risk of developing the chronic breathing condition.
Dr Marc Nickmilder and his colleagues examined some 847 adolescents, with an average age of 15, attending three Belgian secondary schools offering swimming lessons as part of the curriculum. One school used a non-chlorinated pool which meant its pupils could be used as a control group.
Questionnaires, detailing family history of asthma and the number of hours spent in chlorinated and non-chlorinated, enclosed and open-air pools, were completed by parents. And the pupils themselves underwent blood tests to measure levels of immunoglobulin (IgE), an antibody associated with an increased risk of asthma and allergies.
Results presented at the ERS annual meeting yesterday show that the adolescents who had spent more than 500 hours in open-air swimming pools were three times more likely to develop asthma than those who had never used a chlorinated pool.
"Use of open-air swimming pools correlates strongly with atopy [ allergy] levels as measured by blood IgE concentration and considerably increases the asthma risk," Dr Nickmilder explained.
Chlorine gas is a known respiratory irritant which increases the reactivity of airways in the lungs. Research published earlier this year revealed that the respiratory systems of swimming instructors and poolside staff were also affected by continued exposure to chlorine.
Symptoms of asthma include wheeze, shortness of breath and cough which develop when the large- and medium-sized breathing tubes in the lung become inflamed and constrict.
It is estimated that about half of asthma cases have an environmental cause, with the other 50 per cent due to genetic factors.
Latest figures suggest that 15 per cent of children aged 13-14 years in the Republic have asthma, while there are some 470,000 people here with the disease.
Commenting on yesterday's research, Dr John Faul, consultant respiratory physician at the Asthma Research Centre, Connolly Hospital, Blanchardstown, questioned whether it was applicable to children undertaking recreational swimming.
"There are many factors involved in asthma: a prolonged exposure to chlorine in swimming pools might contribute to asthma to a small extent. This research does not show a cause and effect, just an association," he said.