Economic development linked to differences in rates of asthma symptoms

Children with allergic sensitizations in economically developed countries are much more likely to develop asthma than similarly sensitized children in poorer countries, according to a team of international researchers.

The global research study is the first to link economic development to differences in rates of asthma symptoms and allergic sensitization, based on examination of a large, multi-center cross-sectional study of 8- to 12-year-old children who participated in Phase Two of the International Study of Asthma and Allergy in Childhood (ISAAC).

The findings were published in the second issue for September 2007 of the American Thoracic Society's American Journal of Respiratory and Critical Care Medicine.

“Atopic sensitization has long been known to be related to childhood asthma,” wrote Gudrun Weinmayr, M.D., M.P.H., of the Institute of Epidemiology of Ulm University in Germany, and lead investigator of the study. Dr. Weinmayr noted that the strongest relationships have been found in studies in affluent western countries. “Thus, it may be that the link between asthma and atopic sensitization differs between countries.”

Dr. Weinmayr and colleagues evaluated parents' answers about their children's respiratory symptoms from over 54,000 standardized questionnaires; assessed the results of more than 31,000 skin-prick tests; and analyzed the serum levels of allergen-specific IgE in nearly 9,000 children from 22 countries, from rural African to urban Europe.

They then determined the degree to which allergic sensitizations and asthma symptoms varied with the gross national income per capita (GNI) of the country from which they were collected.

“We observed large variations in the prevalence of asthma symptoms and of atopic sensitization among populations,” wrote Dr. Gundmayr. The association between current wheeze, an indicator of asthma, and skin prick sensitivity, an indicator of allergic reaction, was strong in virtually all affluent countries, but much weaker in less affluent settings.

Altogether, children living in affluent countries with allergic sensitizations were 4 times as likely to have asthma than their non-sensitized counterparts; in non-affluent countries, children with allergic responses were only 2.2 times as likely to have asthma.

“This means that local environmental factors may affect asthma and allergy in different ways,” said Renato T. Stein, M.D., Ph.D., of the Pontificia Universidade Catolica do Rio Grande do Sul, in Brazil, another researcher involved in the study.

“Another way to interpret these findings is that asthma in [more affluent] cities is predominantly atopic asthma, while in socially less developed areas asthma may be more of the non-atopic phenotype,” said Dr. Stein.

The researchers speculated that a possible explanation could be that some factors that protect children with allergic sensitization from developing asthma are less present in affluent settings, or that acquired commensal bacteria (gut flora), which may also differ with GNI, play a role in development of tolerance and immune function.

“A wide range of different factors, including nutrition, microbial and allergen exposure, housing conditions, and exposure to pollutants, and so forth may have played a role,” they wrote, remarking that a “center level correlation with GNI does not imply a similar relation at the individual level with personal wealth.”

The research will continue with further investigations in other risk factors in asthma development, including diet, the presence of rhinitis, and eczema. “Data to study the impact of genetics in asthma and allergies has been collected and is a central part in the next steps of this study,” said Dr. Stein.