An estimated 14% of chronic childhood asthma cases may be due to exposure to road traffic pollution, new research indicates.

Some 470,000 people in Ireland have asthma, including one in five children.

According to European scientists, until now, traffic pollution was seen only as a trigger of asthma symptoms, rather than a cause.

They noted that these results are similar to those relating to passive smoking. The World Heath Organisation currently estimates that up to 18% of childhood asthma cases are linked to passive smoking.

This latest research was carried out in 10 European cities, including Barcelona, Brussels, Rome, Stockholm and Vienna. The scientists used a method to assess the impact of traffic pollution on nearby roads.

They found that 14% of chronic asthma cases in children could be attributed to nearby traffic pollution

"Air pollution has previously been seen to trigger symptoms, but this is the first time we have estimated the percentage of cases that might not have occurred if Europeans had not been exposed to road traffic pollution," explained the study's lead author, Dr Laura Perez, of the Swiss Tropical and Public Health Institute.

She added that these results should be considered ‘to improve policy making and urban planning'.

Details of these findings are published in the European Respiratory Journal.

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