Introduction: It is the general impression that the prevalence of asthma is rising. We investigated the prevalence, respiratory symptoms, smoking habits, and lung function in young adults in the City of Copenhagen at an interval of 15 years.
Methods: Men and women aged 20-35 years were sampled from the general population living in a defined area of central Copenhagen. The first examination took place from 1976 to 1978 and comprised 1,034 subjects. A second sample, comprising 1,104 subjects from the same area was examined 15 years later in 1991-1994. All the participants answered a questionnaire about respiration and a spirometry was performed, with measurement of FEV1 and FVC.
Results: The prevalence of self-reported asthma rose from 1.5% in the first survey to 4.8% in the second (p < 0.001). The asthmatics had, on average, poorer lung function than non-asthmatics in terms of FEV1, and this difference was more pronounced in the second survey than in the first. The number of smokers fell significantly from 62% in 1976-1978 to 45% in 1991-1994 (p < 0.001).
Conclusion: The prevalence of self-reported asthma has risen significantly in young adults in Copenhagen over a 15-year period. The severity, as judged by the level of FEV1, has also increased. These findings cannot be explained by changes in smoking habits.