Lung cancer, smoking, and environment: a cohort study of the Danish population

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Abstract
Objective: The almost twofold difference in lung cancer incidence between people living in Copenhagen and in the rural areas of Denmark in the 1980s led to public concern; this study was undertaken to assess the effects of air pollution and occupation on lung cancer in Denmark, with control for smoking habits. Design: Cohort study of national population. Subjects: People aged 30-64 and economically active in 1970 (927 470 men and 486 130 women). Main outcome measures: Relative risks for lung cancer estimated with multiplicative Poisson modelling of incidence rates. Results: Differences in smoking habit explained about 60% of the excess lung cancer risk in Copenhagen for men and 90% for women. After control for smoking, workers had double the lung cancer risk of teachers and academics. There was only a small independent effect of region. Conclusion: Smoking is the main factor behind the regional differences in lung cancer incidence in Denmark, and occupational risk factors also seem to have an important role. The outdoor air in Copenhagen around 1970 contained on average 50-80 µg/m3 of sulphur dioxide, 80-100 µg/m3 total suspended particulate matter, and up to 10 ng/m3 benzo(a)pyrene and had peak values of daily smoke of 120 µg/m3. Region had only a small effect on incidence of lung cancer in the present study, which suggests that an influence of outdoor air pollution on lung cancer is identifiable only above this pollution level. This cohort study of the national population shows that smoking explained about 60% of the excess lung cancer risk in Copenhagen for men and 90% for women After control for smoking, however, workers had double the cancer risk of teachers or academics, whereas there was only a small independent effect of region The outdoor air in Copenhagen around 1970 contained on average 50-80 µg/m3 of sulphur dioxide, 80-100 µg/m3 total suspended particulate matter, and up to 10 ng/m3 benzo(a)pyrene and had peak values of daily smoke of 120 µg/m3 The fact that only a small effect of region on lung cancer incidence was seen in the present study indicates that an influence of outdoor air pollution on lung cancer is identifiable only above this pollution level