UP to a third of new cases of childhood asthma in Europe could be caused by air pollution, a study suggests.

Hundreds of thousands of children from one to 14 years old are believed to have been made ill each year by breathing in pollutants, researchers estimate. Around 1.1 million children are believed to suffer from asthma in the UK.

It is thought that pollution from traffic can damage airways, leading to inflammation and the development of asthma in children who are genetically predisposed to the condition.

The study, led by the Barcelona Institute for Global Health (ISGlobal), looked at the burden of asthma on 63,442,419 children across 18 European countries, including the UK.

They compared asthma incidence rates with estimations of levels of exposure to pollutants in more than 1.5 million square km areas, which are often traffic-related in urban areas.

Finally, they estimated how rates could be affected if levels were reduced in two different scenarios.

They found that 11.4% of the total cases of asthma (66,567) could be prevented each year if countries adhered to the maximum air pollution levels recommended by the World Health Organisation (WHO) for the tiny particles known as PM2.5. This equates to more than 10,000 cases in the UK being prevented annually.

But only 0.4% (2434 cases) across the countries would be prevented with the reduction of another pollutant, nitrogen dioxide (NO2), which is a better marker of traffic sources.

The researchers said they believe these guidelines are outdated and need to be lowered.

If countries went further, tens of thousands more cases of childhood asthma could be avoided, the researchers predict.

In the UK, 44,895 cases (29% of the UK total) could be avoided if the country reduced air pollution to the lowest levels recorded in 41 previous studies.

And 191,883 cases (33%) could be avoided each year across the 18 countries in the study.

For the N02 pollutant, 135,257 (23%) could be stopped if the countries adhered to the lowest levels – 40,000 of which were in the UK (26% of the UK total).

If a third pollutant, black carbon, was reduced to the lowest levels, 19,139 UK cases and 89,191 cases across the 18 countries could be avoided annually.

The study was published in the European Respiratory Journal.