Health: Pollution not to blame for childhood asthma

Teenagers are more likely to suffer from asthma in the clean air of rural Britain than they are in the polluted inner cities. Jeremy Laurance, Health Editor, examines a study which suggests the disease cannot be blamed on climate, diet or air quality.

Britain has one of the highest levels of asthma in the world, and it is now the most common chronic childhood disease. But although childhood asthma has risen sharply over the past few decades, scientists remain baffled about the cause. The mystery will be deepened by the findings of a study of more than 27,000 schoolchildren from all parts of Britain which showed that one in three reported some form of wheezing. Levels were, unexpectedly, slightly higher in rural areas and in Scotland, suggesting that the most popular suspect, pollution, is not the cause.

The evenness of the geographical spread also suggests that climate and diet are unlikely to be factors. The study did find, however, that the disease is underdiagnosed and undertreated, with only 60 per cent of those reporting wheezing getting any treatment.

The researchers, from St George's Hospital Medical School, London, sent questionnaires to 93 large secondary schools across Britain, from the Shetland Islands to Cornwall.

All pupils aged 12-14 were asked to fill them in and 85 per cent were returned. Although one in three pupils said he or she had experienced wheezing in the last 12 months, only half had been diagnosed with asthma. Among those who reported frequent wheezing at night, only one third had been diagnosed with asthma.

Many pupils were not getting the treatment they needed, the researchers say in the British Medical Journal. They estimate that six to seven pupils at each large secondary school are suffering moderate to severe symptoms but are undiagnosed and untreated. Even among those who had been diagnosed, 4 per cent said they were suffering disruption to their lives, suggesting inadequate treatment.

The researchers say the lack of geographical variation in the numbers of children affected suggests that whatever is causing the disease is everywhere. "Furthermore it suggests that factors which do vary geographically in Great Britain - such as climate, diet and outdoor environment - are not the main determinants of prevalence."

Dr Balvinder Kaur, clinical lecturer in public health medicine at St George's, who led the research, said: "The most striking thing was that the prevalence was high. The second most striking thing was that it was high everywhere. I would have expected higher levels in the cities where there is outdoor air pollution, but they were actually higher in non-metropolitan areas. We know pollution triggers asthma attacks in people who have the disease but it does not seem to be a cause of the disease itself."

The level of asthma in France is half that in Britain and it varies widely around the world. The variation is partly attributed to differences in awareness and definition of wheezing but even after these are allowed for, researchers believe real differences remain which could be linked with diet, climate or other factors.