Background: Low socio-economic status is often related to health problems; however, previous studies on asthma, usually cross-sectional, yield inconsistent results. In this study, longitudinal and cross-sectional data on the association between socio-economic status and asthma as well as respiratory symptoms among adults are presented.
Methods: A postal questionnaire was sent on two occasions, 1996 and 2006, to a randomly selected sample of subjects aged 20-69 years in 1996. In total, 4479 subjects participated in both surveys. The questionnaire included questions on asthma, respiratory symptoms and possible determinants. Logistic regression analysis, adjusted for potential confounders, was used to study the association between asthma, respiratory symptoms and socio-economic status.
Results: Manual workers in service had the highest prevalence and cumulative incidence for all investigated symptoms and asthma. Despite a large decrease in smokers, the increase in incident bronchitic symptoms was higher than the increase of incident asthma and incident asthmatic symptoms. Low socio-economic status, rhinitis and a family history of asthma were risk factors for having and developing asthma and respiratory symptoms.
Conclusion: Low socio-economic status is significantly associated with an increased risk for prevalent and incident asthma and respiratory symptoms in this longitudinal population-based survey. The increase in risk was most pronounced in manual workers. Several studies have recently shown an association between low socio-economic status and respiratory symptoms and we conclude that asthma can not be considered as a disease that mainly affects the middle and upper socio-economic classes.