Background: Although the prevalence of asthma and morbidity related to asthma are increasing, little is known about the natural history of lung function in adults with this disease.
Methods: We used data from a longitudinal epidemiologic study of the general population in a Danish city, the Copenhagen City Heart Study, to analyze changes over time in the forced expiratory volume in one second (FEV1) in adults with self-reported asthma and adults without asthma. The study was conducted between 1976 and 1994; for each patient, three measurements of lung function were obtained over a 15-year period. The final data set consisted of measurements from 17,506 subjects (8136 men and 9370 women), of whom 1095 had asthma.
Results: Among subjects who participated in all three evaluations, the unadjusted decline in FEV1 among subjects with asthma was 38 ml per year, as compared with 22 ml per year in those without asthma. The decline in FEV1 normalized for height (FEV1 divided by the square of the height in meters) was greater among the subjects with asthma than among those without the disease (P<0.001). Among both men and women, and among both smokers and nonsmokers, subjects with asthma had greater declines in FEV1 over time than those without asthma (P<0.001). At the age of 60 years, a 175-cm-tall nonsmoking man without asthma had an average FEV1 of 3.05 liters, as compared with 1.99 liters for a man of similar age and height who smoked and had asthma.
Conclusions: In a sample of the general population, people who identified themselves as having asthma had substantially greater declines in FEV1 over time than those who did not.