The prevalence of asthma and allergy continues to increase practically everywhere, and the main cause is the environment. That's the striking conclusion of a just-completed worldwide survey.
The survey, which covered some 140,000 persons aged between 20 and 44, in Europe and beyond, confirms not only that the prevalence of asthma and allergy is still increasing, but also that the countries in the survey were very differently affected, with variations in the ratio of up to 1 to 4 or 1 to 8 depending on the pathologies.
Such variations do not occur by chance, however, according to the authors in the September issue of the European Respiratory Journal (ERJ), the peer-reviewed publication of the European Respiratory Society (ERS).
The data gathered in 22 countries indicate very clearly that the environment and lifestyles are chiefly to blame.
This is the first time that the European Community Respiratory Health Survey (ECRHS) has published a global assessment, after 10 years' work, just as the second phase, ECRHS II, is beginning.
This international survey is a real epidemiological gold mine that extends well beyond the frontiers of Europe. Apart from covering practically all the countries of the European Union, the ECRHS contains information on Iceland, Estonia, Switzerland, Algeria, India, New Zealand, Australia and the USA.
(Canada and Poland also contributed to the survey, but at a later stage, so that the data from those two countries were not taken into account in the analysis that appears in the September issue of ERJ.)
No less than 48 world centers representing 22 countries took part in the initial phase of the ECRHS, gathering data on some 140,000 individuals. Each center processed data on 3,000 to 4,000 subjects, half of whom were men and half women.
Such exceptionally extensive coverage greatly reduces the risk of arriving at the wrong conclusions. But there are more features, of which the lead author of the ERJ article, Christer Janson, of the University of Uppsala in Sweden, is particularly proud:
"The ECRHS is the first study to assess the geographical variations of asthma and allergic diseases in a large number of countries, using the same technique and following two procedures. First, we used identical standardized protocol for all the different areas, so that we can be quite sure that the variations we have shown are real. Second, we combined subjective and objective measurements, and the good thing is that both approaches indicate the same, quite marked pattern of geographical variations in asthma and allergic diseases."
The prevalence of asthma can vary by a factor of 1 to 6 from one country to another.
To say the pattern is marked is not exaggerated, since the results published in ERJ show variations of 1 to 6 for asthma (from 2 to 12% of individuals), of 1 to 4 for allergic rhinitis (from 10 to 40%), and even of 1 to 8 (from 3.5 to 28%) for bronchial hyperreactivity.
Generally speaking, the prevalence of asthmatic and allergic disorders is highest in the English-speaking regions, namely Australia, New Zealand, the United States, Ireland and the United Kingdom.
The prevalence is lowest, on the other hand, in the Mediterranean countries, in Iceland, in Eastern Europe and in India.
For Christer Janson, the message is clear:
"The fact that we can actually show these geographical variations indicates that for some reasons, asthma has developed more quickly in some countries than in others. This suggests that the differences are probably not related to genetic differences and that they are due to some environmental factors, not only pollution and so on, but also the food people eat and the way they live, that promote a high prevalence of asthma in some areas and not in others."
The ECRHS was the first to highlight these geographical variations, a trend later confirmed in the ISAAC survey, which concentrated on children.
Many researchers then tried to discover which factors, in childhood, could explain the geographical variations observed later in life. Suspicions centered on standards of hygiene, infections (some of which protect against certain allergies, while others favor the development of an asthmatic condition), eating habits, or rural and urban environments.
Even the climate was blamed, some claiming that the risk of asthma was less in sunny regions and others maintaining that the risk was worse by the sea.
"In actual fact," Christer Janson points out, "out of many possible candidates, few stand out for certain. What we do know is that it cannot be just one environmental factor. There must be several involved and of course they interact with the genetic factors."
"All we can say for sure at this stage," Janson continues, "is that one of the factors that increases the risk of asthma in adults is occupational exposure to biological and mineral dust."
The ECRHS has also looked into the potential role of major allergens in the development of asthma. What emerged was a link not so much with seasonal allergens as with those that people live with continually, such as dust mites and pet hair.
The ECRHS has already started phase 2, in which subjects who took part in phase 1 will be re-examined 10 years further on.
The aim of this new survey will be to examine all the factors that explain not only the cause of asthma but also the means of securing protection against the disease.
The result should be better strategies, both for prevention and for treatment.
[Contact: Christer Janson]