And drinking chlorinated water – much better if it is fluoridated too – is even “better” for your health.
Children who swim regularly in chlorinated pools are five times more likely to develop asthma, research has found.
Swimming is recommended as a good form of exercise for asthmatics because the warm humid air is less likely to trigger attacks than other physical activities.
But mounting research is suggesting that the chlorine used to keep the pools clean could be contributing to the development of the condition.
Researchers in Belgium studied the effects of swimming in outdoor pools regularly from a young age and found a strong link.
Previously the same team have found that indoor pools may also increase the risk of asthma in children.
It is thought the chlorine fumes floating around the surface of the pool may help to trigger the condition by irritating the upper airways.
There are five million people in the UK with asthma including more than one million children.
Prof Alfred Bernard, of the Catholic University of Louvain, Brussels, Belgium and his team examined 847 secondary school pupils with an average age of 15.
They had blood tests, lung function tests and parents completed a questionnaire about their exposure to pets, tobacco smoke, and pollution which are known to increase the risk of asthma. They were also asked detailed questions about their swimming habits and from that the researchers calculated the total number of hours spent in outdoor chlorinated pools during their life.
Children who had swum for the equivalent of one hour a week for ten years, more than 500 hours in total, were five times more likely to have the wheezing condition than children who never swam in outdoor pools.
Those with a predisposition to allergies, as shown by measurements taken from their blood, were up to ten times more likely to have asthma if they had swam for more than 500 hours in an outdoor pool, the study published in the European Respiratory Journal showed.
Children who had never swum in an outdoor pool and had only swum in an indoor pool for less than 100 hours in their lives were four times less likely to have asthma than the rest of the children studied.
The research team also found that children having regularly attended an outdoor pool before the age of seven were more likely to be allergic to cat or dust mite than those who had never attended an outdoor pool so young.
But children who swam in a pool sanitised using copper and silver showed no increased risk of asthma which suggests the chemicals and not simply swimming are responsible for the effect, the authors said.
The authors concluded: “In summary, the present study shows that the attendance at outdoor chlorinated swimming pools, at home or during holidays, is associated with an exposure-dependent increase in the risk of asthma.
“Since these associations were not found with the attendance of the copper-silver pool, they are most likely due to some airways damage caused by chlorine-based oxidants added to pool water or released at the surface of the pool as aerosols or gases.”
The researchers advise parents not to over-chlorinate their own pool and not to send their children too frequently to poorly managed outdoor pools with a strong chlorine smell at their surface.
The most common way to add copper and silver to a pool is with a machine called an Ioniser, which attaches to the pipework and runs on electricity.
They have a copper and silver electrode that erodes away over time as the pool water passes over it with charged copper and silver atoms being released into the water.
Leanne Male, Assistant Director of Research at Asthma UK, said: “There are a number of studies to suggest that chemicals such as chlorine might be involved in the development or aggravation of allergic conditions including asthma. This is due to the fact that chlorine products may compromise protective cell barriers within the lungs, meaning people with allergic asthma are more vulnerable to allergens.
“However, for people with non-allergic asthma, swimming is an excellent way to keep fit and increase lung capacity especially in indoor pools as the warm humid air in the swimming pool is less likely to trigger asthma symptoms.”
By Rebecca Smith, Medical Editor
Last Updated: 2:05AM BST 25 Sep 2008
Source: The Telegraph