Socioeconomic status, lung function and admission to hospital for COPD: results from the Copenhagen City Heart Study

Abstract

This study analysed the effect of education and income on development of chronic obstructive pulmonary disease (COPD) assessing lung function and hospital admission. The study population consisted of 14,223 subjects, aged 20-90 yrs, randomly sampled from the population of Copenhagen in 1976. Association between socioeconomic factors and forced expiratory volume in one second (FEV1) and forced vital capacity (FVC) at study entry was analysed by linear regression. The relation between socioeconomic factors and risk of admission to hospital for COPD from study entry until 1993 was assessed by register linkage. Education and income were independently associated with FEV1 and FVC. The age- and height-adjusted difference in FEV1 (mean+/-SEM) between the highest and lowest level of education and income was 259+/-31 mL in females and 400+/-39 mL in males. After additional adjustment for quantity and duration of smoking and inhalation, the difference was 220+/-31 mL and 363+/-39 mL in females and males, respectively. Results for FVC were of the same magnitude. Using a socioeconomic index which combined information on education and household income the association with lung function did not differ by age. A total of 219 females and 265 males were admitted to hospital for COPD during follow-up. Education and income were significantly associated with admission to hospital. After detailed adjustment for smoking the relative risks (95% confidence intervals) for medium and high versus low socioeconomic index in females were 0.74 (0.55-1.02) and 0.27 (0.10-0.73), respectively. Corresponding relative risks in males were 0.47 (0.36-0.63) and 0.35 (0.17-0.70). The results indicate that socioeconomic factors operating from early in life affect the adult risk of developing chronic obstructive pulmonary disease independently of smoking in both females and males.