Why children are allergic to affluence
Allergies such as asthma have more to do with vaccines than air pollution, says Dr James Le Fanu
Besides its great natural beauty, the Isle of Skye is one of the least polluted parts of the kingdom no toxic emissions from factory chimneys, no traffic-congested roads contaminating the air with acid aerosols and sulphur dioxide. Indeed, virtually the only man-made airborne pollutant is the smoke from household fires rapidly dispersed by the prevailing winds from the Atlantic.
And yet when Dr Jane Austin, paediatrician at Invernesss Royal Northern Infirmary, investigated the prevalence of asthma among the children of school age on the island, she found it to be commoner than in the rest of the Highlands, commoner than in Aberdeen, commoner even than in Cardiff. Her careful measurements of lung function showed a deterioration following exertion in onethird of the islands schoolchildren, while the equivalent figure in Cardiff is 8 per cent.
Dr Austins findings are quite unexceptional; doctors and scientists have found little or no relationship between the severity of airborne pollution and the numbers affected by asthma. Certainly those who already have asthma are often made wheezier and more short of breath by the photochemical smog from vehicle exhausts, but pollution does not seem to cause the illness or account for its increased frequency.
"There is no evidence of the significant rise in pollutants that would have been necessary to cause the increase in asthma," says Professor Anthony Seaton, of Aberdeen University, citing as evidence a remarkable study of children in Leipzig and Munich. Before the fall of the Berlin Wall, most of the factories in East Germany manufactured little else other than pollution, and Leipzig was no exception. In 1989 the concentrations of sulphur dioxide and particulate matter in the air were respectively 30 and 10 times higher than in Munich, and yet the study found asthma to be commoner in Munich than in smog-ridden Leipzig.
There is a profound disparity between popular belief and expert opinion on this matter. While for the public and environmentalists a causative link between air pollution and asthma is self-evident, the experts are not convinced. "Air pollution as a cause of asthma has the seeming merit of appealing to common sense," wrote Anthony Newman Taylor, professor of respiratory medicine at Londons Royal Brompton Hospital in The Lancet earlier this year (and one does not get a more authoritative opinion than that), yet the relationship, he says, "has not been observed."
So why do people, particularly children, suffer from asthma? Along with eczema and hay fever, asthma is one of three allergic illnesses with much in common. These atopic diseases are characterised by an excess production of an antibody called IgE which, in the presence of some allergens, causes symptoms. Thus for the atopic individuala high pollen count may cause the itchy eyes and runny nose of hay fever; chemicals and foods may cause the itchy, dry skin of eczema, while air pollutants, the house-dust mite and viral infections may cause the asthma wheeze.
The main features of these three atopic illnesses are remarkably similar. They all run strongly in families and interdependently, suggesting that the same genes are involved. Thus, those with asthma are much more likely, to suffer from eczema and hay fever, and their children are much more likely to suffer from these illnesses. They all tend to start in childhood and get better or disappear altogether with the passage of time. They have all become a lot more frequent since the war as shown by a comparative study of thousands of children in Aberdeen, in 1964 and 1989. Over this 25-year period, the prevalence of asthma and eczema doubled and that of hay fever trebled.
They are also, virtually uniquely , "diseases of the advantaged" --they occur more frequently in children born into professional compared to working-class households. They are also more common in small rather than large families "only" children are four times more likely to develop hay fever than those with several siblings and three times more likely to develop eczema. Further, as already noted, asthma seems to be commoner in isolated communities such as Skye than in towns, and in affluent cities such as Munich than in impoverished Leipzig.
Clearly, then, something to do with the bodys immune system has changed, in-creasing the prevalence of these three illnesses. The obvious candidate that fits in with all the other observations to do with social class and family size is the decline in exposure to infection. Commenting on the relationship between eczema, hay fever and family size, Dr David Strachan, senior lecturer at St Georges Hospital medical school, observes it is best explained "if allergic diseases are prevented by infections in early childhood transmitted by contact with older siblings". Last month, Professor Newman Taylor made a similar point about asthma which he says may have reached "epidemic status in affluent societies because falling family size reduces the chances that toddlers and infants encounter infections sufficiently early". The rise in atopic illness certainly coincides with the precipitous decline during the postwar years in the major childhood infectious diseases, so perhaps they are the price that has to be paid for modem vaccines, the miracle of antibiotics and social progress.