The prevalence of childhood asthma and wheeze rises around 2 to 3 per cent for every indoor swimming pool per 100,000 of the population across Europe, indicates research published ahead of print in Occupational and Environmental Medicine.
The researchers analysed the rates of wheezing, asthma, hay fever, allergic rhinitis, and atopic eczema, reported in the International Study of Asthma and Allergies in Childhood (ISAAC), by video or written questionnaire.
The study involved almost 190,000 young teenagers (13 and 14 year olds) from 21 countries across Europe.
These figures were then set in the context of the number of indoor chlorinated swimming pools per 100,000 of the population in each of the countries.
The number of indoor pools varied by a factor of 20 between Eastern and Western Europe, ranging from one pool for every 50,000 inhabitants in Western Europe to one for every 300,000 inhabitants in Eastern Europe.
The number of indoor pools also varied fivefold within individual countries, including Italy, Spain, and the UK.
After taking account of potential influential factors, such as the gross domestic product (GDP) of a country, climate, and altitude, the prevalence of asthma and wheeze was strongly associated with the number of indoor pools per 100,000 of the population.
The findings showed a clear East-West divide in indoor pool availability and rates of asthma.
The rate of wheezing rose by 3.39 per cent for every additional indoor chlorinated swimming pool. Similarly, the rate of asthma rose by 2.73 per cent.
The authors conclude that the rise of asthma in Western Europe could at least partly be attributed to the increasing exposure of children to the by-products of chlorine in the air and water of indoor swimming pools.
They suggest that the long term effects of chlorine by-products on children's respiratory health should be thoroughly evaluated, and that pools should be properly ventilated and levels of chlorine by-products regulated.