A survey published in the Journal of Occupational and Environmental Medicine indicates that a connection could be drawn between a sharp increase in the number of cases of asthma in children and the chlorine used in swimming pools.

Researchers at the Catholic University of Louvain in Brussels carried out tests on 226 primary school children who swam regularly in indoor chlorinated pools and had done since early childhood. Note was also taken of environmental and lifestyle factors likely to affect the results of the tests.

Similar tests were also undertaken on a group of 16 children and 13 adults, both before and after a visit to an indoor chlorinated pool.

Chlorine in water releases a strong oxidant which, when reacting with organic matter such as urine or sweat, generates a mixture of potentially harmful disinfection byproducts. These are then inhaled by swimmers, either as gases or in the form of aerosols, depending on the compound in question.

The most volatile of these is nitrogen trichloride, a powerful irritant and probably responsible for the eye and breathing problems experienced by pool staff and visitors

The report also says that apart from a limited study on lifeguards, no research has been done into whether or not chlorine and its byproducts in a swimming pool can be a health hazard.

It also points out that the belief the pool environment is safe has had the result of most countries focusing their swimming pool regulatory framework on the microbiological quality of the water, rather than the air quality.

Also noted is the practice of encouraging school children to swim as frequently as possible, in the belief that the swimming pool environment is safe.

The conclusion of the study is – although it recommends that further research be undertaken to test the theory – that regular attendance at a chlorinated pool by young children could increase their risk of developing asthma and be an important cause of the rising number of cases of childhood asthma.

It further stated that: "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 reinforce water and air quality control in indoor pools in order to minimise exposure to these reactive chemicals."

In response to the researchers findings, Professor Martyn Partridge of the UK’s National Asthma Campaign is quoted as saying: "Great care must be taken in interpreting such associations. It is very unlikely that swimming by itself could be the cause for the increase in asthma."

He said he welcomed research such as that in the Brussels study, but felt that much more work needed to be done before any conclusions could be drawn.

Major risk factors also include obesity, genetic predisposition, smoking, low birthweight, air pollution and allergens. Details: www.oem.bmjjournals.com