PARIS, May 29 (AFP) - Chlorine used to disinfect indoor swimming pools could be one of the causes behind an astonishing surge in childhood asthma in developed countries in the past few decades, according to a new study.
The suspected culprit is trichloramine, a gassy, easily inhalable irritant that is released in a complex process when chlorinated water reacts with urine, sweat or other organic matter brought by swimmers.
Trichloramine has previously been fingered as a trigger for three proteins that destroy the cellular barrier protecting the lungs, making it permeable and more prone to the passage of allergens -- the substances that unleash an asthma attack.
Belgian researchers, writing in the British research journal Occupational and Environmental Medicine, took blood samples from 226 young primary schoolchildren who had swum regularly at indoor pools since early childhood.
They also took samples from 29 adults and children both before and after a session in an indoor pool.
The samples show that youngsters who regularly attend indoor pools accumulate these proteins, making them more at risk from asthma.
Most frightening of all: the children who swam most frequently had protein levels of the kind found in regular smokers.
Protein levels even rose measurably among people who had been sitting at the poolside and had not swum.
"The increasing exposure of chlorination products in indoor pools might be an important cause of the rising incidence of childhood asthma and allergic disease in industrialised countries," say the scientists, led by Alfred Bernard, a toxicologist at Brussels' Catholic University of Louvain.
The effects were the same for children wherever they lived, and remained after taking account of other environmental pollutants. But they were strongest in the youngest children.
Levels of trichloramine -- chemical name nitrogen trichloride (NCl 3) -- vary a lot, however.
It depends on how crowded the pool is, the ventilation and how clean the swimmers are.
Chlorine has been used for several decades to kill bacteria in indoor pools.
But the authors were astounded when they unable to locate a single serious study to check whether this or other disinfectant chemicals pose a risk for swimmers, especially youngsters who are the most frequent users.
"The belief that the swimming pool environment is safe is so deeply rooted in our minds that it is regarded as a healthy practice to send schoolchildren swimming as frequently as possible -- much more than necessary for swimming training -- even from the youngest age," they say.
When it comes to pool hygiene, most countries focus on bacterial levels in the pool, but never the air quality.
"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, in order to minimise exposure to these reactive chemicals," the authors say.
In the United States alone, some 17.3 million people suffer from asthma. Since 1980, hospitalisation of patients and deaths occurring from asthma in the United States have risen 75 percent.
According to a 2002 study, one in eight British children suffers from asthma while one in five has been diagnosed with the illness at some stage in their life.
Significant risk factors in asthma include obesity, genetic predisposition, smoking, low birth weight, air pollution and allergens, such as exhaust particles, smoking and household dust mites. Strong emotions and even the weather can exacerbate the condition.
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