Air pollution is not the cause of the epidemic of asthma in adults and children, scientists said yesterday, and they warned that infections and allergens are more potent triggers of the disease.
A two-year independent inquiry has concluded that although air pollution may provoke acute asthma attacks or aggravate existing chronic disease, the effect is "generally small and ... appears to be relatively unimportant" compared with other factors such as viruses, cigarette smoke, diet and house dust-mite droppings.
Professor Stephen Holgate, chairman of the Committee on the Medical Effects of Air, which compiled the report, said that the strongest risk state for asthma was allergy and this was rising across the developed world.
"The real concern to the public is the rising trend in asthma," he said. "The important questions are what is driving the increase in allergies and why do they manifest themselves as airway disease ... Outdoor air pollution seems not to be a particularly important cause [of asthma]."
The committee decided that an outbreak of asthma in July 1994, following a period of hot weather and thunderstorms, was not related to an increase in air pollution, Professor Ross Anderson, a member of the committee, said.
"Every epidemic so far has been associated with greater concentration of allergens in the air. These allergens include biological pollutants such as pollen and fungal spores which were not considered by the committee, which focused instead on chemical pollutants," he said.
The inquiry team did find that pollution due to car and lorry emissions may pose an increased risk. Professor Anderson said: "People living close to streets with heavy traffic do appear to have a slightly increased risk."
Asthma has increased by an estimated 50 per cent in the last 30 years, and three million people - one million of them children - are sufferers. The disease has also increased in severity and the number of deaths from asthma has almost doubled since the 1970s to around 2,000 a year. Around 200,000 people are disabled by severe asthma.
Although asthma is regarded as a disease of urbanisation, the committee found "little or no" association between the regional distribution of asthma and that of air pollution. A recent study from the Isle of Skye, where air pollution is believed to be minimal, showed as high a prevalence of asthma as anywhere else in the UK.
Professor Holgate said that other factors associated with urban living, such as cramping of houses and poor ventilation, and lifestyle changes, particularly smoking in pregnancy, diet of the pregnant mother and diet in early life were more significant.
Dr Kenneth Calman, the chief medical officer, said that air pollution remained an important problem because it made some asthmatics worse. Government research commitment to asthma was "intense", he said.
The National Asthma Campaign (NAC), said the report highlighted the need for more research into the causes of asthma. Melinda Letts, chief executive of NAC, said: "We hope the Government will continue to take seriously the impact of traffic pollution can have on some asthma patients."
The Friends of the Earth said the report confirmed the health effects of air pollution, and urged the Government to promote alternatives to cars and lorries.
Register for free to continue reading
Registration is a free and easy way to support our truly independent journalism
By registering, you will also enjoy limited access to Premium articles, exclusive newsletters, commenting, and virtual events with our leading journalists
Already have an account? sign in
Join our new commenting forum
Join thought-provoking conversations, follow other Independent readers and see their replies