health.telegraph.co.uk

The rise in asthma and non-allergic breathing difficulties may be caused by changes in diet or obsessive hygiene in the home, a team of researchers reports. But it has ruled out increased exposure to traffic pollution.

The findings come days after doctors reported that the incidence of nut allergy had doubled since the end of the 1980s. Asthma has reached epidemic proportions in Britain. One in seven children - approximately 1.5 million - now has the disease. The reason why asthma and other auto-immune diseases have increased over the past few decades is still a puzzle.

Some scientists have argued that the obsession with cleanliness is to blame. Babies and children are no longer in contact with the germs needed to prime a healthy immune system. Others argue that fitted carpets, double glazing and central heating increase exposure to house dust mites.

Prof Mike Silverman, an expert in child health at Leicester University who carried out the latest study, said the increase covered all types of wheeze - from insignificant wheezing to severe asthma attacks. The findings, published in The Lancet, come from a comparison of questionnaires sent to the parents of 1,650 children in 1990 with a similar survey of 2,600 children in 1998. All the children were aged between one and five and lived in Leicestershire.

Over the eight years there was a significant rise in all types of wheeze from 16 per cent of children to 29 per cent. The number of asthmatic children rose from 11 per cent to 19 per cent, while the proportion of children admitted to hospital for wheezing increased from six per cent to 10 per cent. There was also an increase in transient wheezing, a condition that normally disappears by school age, from three per cent to five per cent.

The increase was not just linked to allergies. The incidence of viral wheeze, the response to a virus infection, rose from nine per cent to 19 per cent. The rise in respiratory problems could not be linked to household risk factors such as passive smoking, gas cooking, pets or low parental education attainment because those factors declined over the period, the team reports.

Prof Silverman said factors unrelated to allergies were to blame for the rise. But he ruled out traffic pollution as a likely cause. Part of the increase could be due to a greater awareness of wheezing and asthma. But other symptoms of asthma, such as coughing, had not increased over the decade.

He said: "The increasing prevalence of viral asthma can't be explained by allergies. There may be something more fundamental that has made airway diseases increase. We suspect that there is something going on. It may be related to diet, or something developmental in the lungs before and after birth, or it may be connected to the immune system. But we do not think that it is linked to pollution."

Prof Silverman plans to follow up the children in the study to look at levels of atopy, or allergy, and lung function. Dr Martyn Partridge, of the National Asthma Campaign, said: "This interesting study is in line with studies with slightly older children in Australia showing significant increases in the number of children with wheezing disorders over a 10-year period.

"While atopy is a risk factor in the development of wheezing disorders, this study suggests that atopy alone cannot explain the dramatic rise in the number of children suffering from asthma and other wheezing disorders. Further research is clearly needed and Government action necessary to ensure sufficient attention to this increasingly common condition."