Study 'proves' asthma cause

Car exhaust is a major contributer to air pollution

Evidence has been found of a link between air pollution and asthma in children.

Although air pollution has been linked with respiratory problems for some time, proof of a consistent connection has always proved elusive.

But a study published on Friday lends support to a direct association.

The researchers are calling for improved public health strategies to target children at risk.

Children's breathing tested

The study of 632 children aged 7 to 11 years found that respiratory disorders worsened as air pollution increased.

Researchers led by Dr Marike Boezen at the University of Groningen in the Netherlands performed the study and have published their results in The Lancet medical journal.

They divided the children into four groups:

• Those with bronchial hyper-responsiveness, or BHR. This is where the lungs are extremely sensitive to stimuli such as cold air or drugs
• Those who suffered allergies (atopy)
• Those who had neither
• Those who had both

The children, who came from both rural and urban areas, kept a daily diary of any asthma symptoms they suffered and tested their lung capacity three times a day.

Children were divided into four groups

The researchers managed to collect complete data for 459 of the children.

Of these, 119 had both BHR and atopy. When air pollution was higher, these children were significantly more likely to experience breathing problems.

When there were more particulates - pollutants larger than 10 micrometers - in the air, these children were up to 139% more likely to suffer.

And when there were more of the pollutants that make up car exhaust fumes - black smoke, sulphur dioxide and nitrogen dioxide - they were up to 131% more likely to have such symptoms.

First success

Dr Boezen explained how this study proves a link while others could not.

"Our selection criteria based on the clinical characteristics of BHR and allergy is less prone to error than selection criteria based on self-reported chronic respiratory symptoms used in those other studies," she said.

"Moreover, the duration of our study was substantially longer - three months during three winters - than that of other studies, which improved the power of the study to detect air pollution effects."

Dr Boezen called for improved public health strategies to target children at risk.

Cities are notorious for low air quality

"So far, the impression from studies on negative health effects of air pollution seems to be that there in no threshold concentration below which air pollution does not have a negative health effect in certain vulnerable groups of persons.

"The prevalence of respiratory symptoms is linked to increasing levels of air pollution - thus, although over the last decades air pollution levels have decreased, even low levels of air pollution may effect respiratory health.

"Therefore, trying to decrease levels of air pollution even more seems to be a plausible public health measure strategy."

Pollution problems

The National Asthma Campaign also wants pollution reduced.

In a policy statement, it says: "The government must continue to recognise the concern about air pollution among the general public.

"It must demonstrate a commitment to finding long-term solutions tothe problems it poses, not short-term fixes such as 'green fuels'"

However, it is uncertain whether this can be achieved.

Dr Peter Burney, of the Department of Public Health at Guy's and St Thomas's at London, said there were already too many allergens in the air.

He said public health strategies may therefore be better off trying to prevent the symptoms rather than cut levels of air pollution.