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

BMJ 1996;312:1259-1263 (18 May)

Papers

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

Gerda Engholm, statistician,^a Finn Palmgren, senior scientist Correspondence to: Ms Engholm.,^b Elsebeth Lynge, head of department ^a

^a Danish Cancer Society, Division for Cancer Epidemiology, Box 839, DK-2100 Copenhagen (null set), Denmark, ^b National Environmental Research Institute, Box 358, DK-4000 Roskilde, Denmark

Abstract

Objective: The almost twofold difference in lung cancer incidencebetween people living in Copenhagen and in the rural areas ofDenmark in the 1980s led to public concern; this study was undertakento assess the effects of air pollution and occupation on lungcancer 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 estimatedwith multiplicative Poisson modelling of incidence rates.
Results: Differences in smoking habit explained about 60% ofthe excess lung cancer risk in Copenhagen for men and 90% forwomen. After control for smoking, workers had double the lungcancer risk of teachers and academics. There was only a smallindependent effect of region.
Conclusion: Smoking is the main factor behind the regional differencesin lung cancer incidence in Denmark, and occupational risk factorsalso seem to have an important role. The outdoor air in Copenhagenaround 1970 contained on average 50-80 µg/m³ of sulphurdioxide, 80-100 µg/m³ total suspended particulate matter,and up to 10 ng/m³ benzo(a)pyrene and had peak values of dailysmoke of 120 µg/m³. Region had only a small effect onincidence of lung cancer in the present study, which suggeststhat an influence of outdoor air pollution on lung cancer isidentifiable only above this pollution level.

Key messages

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

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