Socioeconomic status and lung cancer incidence in men in The Netherlands: is there a role for occupational exposure?

Our plain-English summary of Socioeconomic status and lung cancer incidence in men in The Netherlands: is there a role for occupational exposure?, by A.J. van Loon, R.A. Goldbohm, I.J. Kant, et al (Journal of Epidemiology and Community Health, 1997).

The study

• Authors: A.J. van Loon, R.A. Goldbohm, I.J. Kant, G.M. Swaen, A.M. Kremer, P.A. van den Brandt
• Journal: Journal of Epidemiology and Community Health
• Published: 1997;51(1):24-9
• Cited by: 29 articles, as counted by NIH iCite
• Read it: PubMed · Publisher · Free full text

Abstract

Study Objective: To evaluate the influence of occupational exposure to carcinogens in explaining the association between socioeconomic status and lung cancer.

Design: A prospective cohort study. Data on diet, other lifestyle factors, sociodemographic characteristics and job history were collected by means of a self administered questionnaire. Follow up for incident cancer was established by record linkage with a national pathology register and with regional cancer registries.

Setting: Population originating from 204 municipalities in The Netherlands.

Participants: These comprised 58 279 men aged 55-69 years in September 1986. After 4.3 years of follow up there were 470 microscopically confirmed incident lung cancer cases with complete data on dietary habits and job history.

Measurements And Main Results: Estimation of occupational exposure to asbestos, paint dust, polycyclic aromatic hydrocarbons, and welding fumes was carried out by two experts, using information on job history from the baseline questionnaire. Socioeconomic status was measured by means of highest attained level of education and two indicators based on occupation. In the initial multivariate analyses of socioeconomic status and lung cancer, adjustment was made for age, smoking habits, intake of vitamin C, beta-carotene and retinol, and history of chronic obstructive pulmonary disease or asthma. Additional adjustment for occupational exposure to the four carcinogens mentioned above did not change the inverse association between the level of education and lung cancer risk (initial model: RR highest/lowest level of education = 0.53; 95% CI 0.34, 0.82; additional model: RR highest/lowest level of education = 0.53; 95% CI 0.34, 0.84). Nor was the association between the two occupation based indicators of socioeconomic status and lung cancer risk influenced by occupational exposure to carcinogens. The effect of occupational exposure on the association between the level of education and lung cancer risk did not differ between ex-smokers and current smokers.

Conclusions: Occupational exposure to asbestos, paint dust, polycyclic aromatic hydrocarbons, and welding fumes could not explain the inverse association between socioeconomic status and lung cancer risk. More research which explicitly addresses possible explanations for the association between socioeconomic status and lung cancer risk is needed.

In plain English

This Dutch prospective cohort study, analysed with a case-cohort approach, asked whether workplace exposure to cancer-causing agents explains the link between lower socioeconomic status and higher lung cancer risk. The Netherlands Cohort Study enrolled 58 279 men aged 55-69 in 1986. After 4.3 years of follow up, 470 lung cancer cases and 1245 members of a random subcohort had complete data. Two experts estimated each man's lifetime exposure to asbestos, paint dust, polycyclic aromatic hydrocarbons and welding fumes from his self-reported job history. Ever exposure to asbestos was assigned to 66 of 470 cases (14.0%) and 109 of 1245 subcohort members (8.8%). Men with higher vocational or university education had a lower lung cancer rate than men with only primary school (rate ratio 0.53; 95% CI 0.34 to 0.82). This allowed for age, smoking, diet and history of lung disease. Adding the four workplace exposures left it at 0.53 (95% CI 0.34 to 0.84). Results within ex-smokers and current smokers changed only marginally. The authors concluded that these exposures could not explain the link. They noted that actual exposure levels could not be estimated, which may cause misclassification.

We wrote this plain-English summary from the full article with the help of AI, and a second AI model checked each sentence against the article. It is not the authors' wording; the abstract and the article are their own account.

What the study did and found

• Design: Prospective cohort study (Netherlands Cohort Study) analysed with a case-cohort approach
• Who was studied: 58 279 men aged 55-69 years from 204 municipalities in The Netherlands, enrolled in 1986 and followed from September 1986 to December 1990 (4.3 years); after exclusions, 470 microscopically confirmed lung cancer cases and 1245 subcohort members were analysed
• Exposure: Occupational exposure to asbestos, paint dust, polycyclic aromatic hydrocarbons (PAHs) and welding fumes, assigned job by job by an occupational hygienist and an occupational epidemiologist from a self-administered job history. Each job was rated as no, possible, probable or nearly certain exposure, and a cumulative index was built from probability weight times years exposed. No asbestos fiber types were specified. The main question was the link between socioeconomic status (education and two occupation-based scores) and lung cancer.
• Main results:
  • A higher proportion of lung cancer cases than subcohort members was ever exposed to each agent. Asbestos: 66 of 470 cases (14.0%) vs 109 of 1245 subcohort members (8.8%). Paint dust: 17 (3.6%) vs 15 (1.2%). PAHs: 31 (6.6%) vs 66 (5.3%). Welding fumes: 59 (12.6%) vs 134 (10.8%).
  • In the subcohort, occupational exposure was most prevalent among men with lower vocational schooling. For asbestos, this was 49 men (18.8%) in that group.
  • Men with the highest education (higher vocational/university) had a lower lung cancer rate than men with primary school only: RR 0.53 (95% CI 0.34, 0.82; trend p less than 0.01). This was adjusted for age, smoking, vitamin C, beta-carotene and retinol intake, and history of COPD or asthma. After further adjustment for the four occupational exposures it was RR 0.53 (95% CI 0.34, 0.84).
  • The non-significant association for the EGP occupation score was RR 0.76 (95% CI 0.49-1.18) for lower white collar vs blue collar. It changed slightly to 0.82 (95% CI 0.52, 1.28) after adjustment for occupational exposures.
  • No association was found between the social standing (U&S) score and lung cancer risk.
  • Within smoking groups, adjustment for occupational exposures made only marginal changes. Among ex-smokers, the rate ratio for higher vocational/university vs primary school went from 0.37 (0.17, 0.82) to 0.41 (0.18, 0.94). Among current smokers it went from 0.60 (0.35, 1.03) to 0.63 (0.36, 1.09).
• The authors' conclusion: The authors concluded that, after adjustment for smoking, diet and lung disease history, an inverse association between socioeconomic status and lung cancer risk remained. Occupational exposure to asbestos, paint dust, PAHs and welding fumes could not explain it. They called for more research addressing possible explanations.
• Limitations the authors state:
  • The job histories did not allow estimation of actual past exposure concentrations, which may lead to misclassification of exposure.
  • Misclassification of smoking habits may lead to residual confounding. The authors judged this unlikely to explain their findings.
  • Non-smokers could not be analysed separately, because only 3 lung cancer cases with complete data were non-smokers.
  • Education is stable over time but may mask later changes in individual circumstances.
  • Psychosocial factors and air pollution, which might help explain the association, could not be investigated in this cohort.

Topics

The National Library of Medicine indexes this study under subjects our site covers: Lung cancer.

Medical terms in this study, explained in our Lexicon: Lung Cancer, Occupational Exposure, Cohort Study, Pathology, Habit.

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