Urban air pollution and lung cancer in Stockholm

Our plain-English summary of Urban air pollution and lung cancer in Stockholm, by F. Nyberg, P. Gustavsson, L. Järup, et al (Epidemiology, 2000).

The study

• Authors: F. Nyberg, P. Gustavsson, L. Järup, T. Bellander, N. Berglind, R. Jakobsson, G. Pershagen
• Journal: Epidemiology
• Published: 2000;11(5):487-95
• Cited by: 246 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

We conducted a population-based case-control study among men 40-75 years of age encompassing all cases of lung cancer 1985-1990 among stable residents of Stockholm County 1950-1990. Questionnaires to subjects or next-of-kin (primarily wives or children) elicited information regarding smoking and other risk factors, including occupational and residential histories. A high response rate (>85%) resulted in 1,042 cases and 2,364 controls. We created retrospective emission databases for NOx/NO2 and SO2 as indicators of air pollution from road traffic and heating, respectively. We estimated local annual source-specific air pollution levels using validated dispersion models and we linked these levels to residential addresses using Geographical Information System (GIS) techniques. Average traffic-related NO2 exposure over 30 years was associated with a relative risk (RR) of 1.2 (95% confidence interval 0.8-1.6) for the top decile of exposure, adjusted for tobacco smoking, socioeconomic status, residential radon, and occupational exposures. The data suggested a considerable latency period; the RR for the top decile of average traffic-related NO2 exposure 20 years previously was 1.4 (1.0-2.0). Little association was observed for SO2. Occupational exposure to asbestos, diesel exhaust, and other combustion products also increased the risk of lung cancer. Our results indicate that urban air pollution increases lung cancer risk and that vehicle emissions may be particularly important.

In plain English

This population-based case-control study in Stockholm County, Sweden, examined whether long-term outdoor air pollution was linked to lung cancer in men aged 40 to 75. It included 1,042 men diagnosed with lung cancer from 1985 to 1990 and 2,364 control men. Questionnaires went to the men or their next of kin. The authors modeled each man's yearly home exposure to nitrogen dioxide from road traffic and sulfur dioxide from heating. They adjusted for smoking, radon, socioeconomic status and workplace exposures, including asbestos. Men in the top tenth of 30-year average traffic-related nitrogen dioxide had a relative risk of 1.17 (95% CI 0.84–1.62) compared with the lowest quarter, which the authors called a weak effect. The same comparison for exposure 21 to 30 years earlier gave 1.44 (1.05–1.99). Sulfur dioxide showed little effect. High workplace asbestos exposure (0.89 fiber-years/mL or more) had a relative risk of 1.47 (1.10–1.97) compared with none or low exposure. The authors concluded that urban air pollution increases lung cancer risk and that vehicle emissions may be particularly important. They noted that their exposure estimates were likely imprecise.

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: Population-based case-control study, with two control groups (population controls and mortality-matched controls) that were combined for the analysis
• Who was studied: Men aged 40 to 75 who lived in Stockholm County, Sweden, at some time from 1985 to 1990 and had lived outside the county for no more than 5 years between 1950 and 1990. The study included 1,042 lung cancer cases (out of 1,196 identified from the regional cancer registry) and 2,364 controls (1,274 population controls and 1,090 mortality-matched controls). Questionnaires were answered by the subjects or by next of kin.
• Exposure: Estimated home exposure, over the 30 years before selection, to nitrogen dioxide from road traffic and sulfur dioxide from heating. These were modeled from historical emission databases and linked to residential addresses using GIS. The analyses also included workplace exposure to diesel exhaust, other combustion products and asbestos, each judged case by case by an occupational hygienist. No asbestos fiber type is named.
• Main results:
  • Traffic-related nitrogen dioxide averaged over 30 years: men in the top category (90th percentile and above) had a relative risk of 1.17 (95% CI 0.84–1.62) compared with men in the lowest quartile when only this pollutant was in the model. The relative risk was 1.28 (0.87–1.88) when sulfur dioxide was also included. The authors described this as a weak effect.
  • Traffic-related nitrogen dioxide averaged over 21 to 30 years before selection (a 20-year lag): men in the top category had a relative risk of 1.44 (95% CI 1.05–1.99) compared with men in the lowest quartile of that time window. The relative risk was 1.60 (1.07–2.39) with sulfur dioxide also in the model. These effects appeared stronger than for the 30-year average.
  • Sulfur dioxide from heating showed little effect in any time window. For the 30-year average, the top category compared with the lowest quartile had a relative risk of 1.00 (95% CI 0.73–1.37).
  • Men with high cumulative workplace asbestos exposure (0.89 fiber-years/mL or more; 133 cases and 175 controls) had a relative risk of lung cancer of 1.47 (95% CI 1.10–1.97) compared with men with none or low exposure. For high diesel exhaust exposure the relative risk was 1.41 (0.97–2.05), and for other combustion products it was 1.47 (1.01–2.14), each compared with none or low exposure.
  • Smoking was the strongest risk factor. Current smokers of more than 20 cigarettes a day had a relative risk of 34.6 (95% CI 23.2–51.6) compared with never smokers.
  • Among heavy smokers (21 or more cigarettes a day), no risk from lagged traffic-related nitrogen dioxide was indicated (relative risk 0.74, 95% CI 0.38–1.45, above versus below the 90th percentile). Among never smokers the relative risk was 1.68 (0.67–4.19).
  • Based on exposure above the 25th percentile, the authors calculated that up to 10% of lung cancer among men aged 40 to 75 in Stockholm County could be related to traffic-related air pollution 20 years earlier.
• The authors' conclusion: The authors concluded that their results indicate that urban air pollution increases lung cancer risk and that vehicle emissions may be particularly important.
• Limitations the authors state:
  • Exposure misclassification that does not differ between cases and controls is probable. It would tend to bias estimates toward finding no effect.
  • The exposure indicators are proxies for a complex pollution mix and are likely subject to measurement error.
  • Particulate air pollution could not be analyzed directly, because historical measurements, past emission data and validated models were lacking.
  • The sulfur dioxide model could not be validated against independent measurements, because all available measurements were used to calibrate it.
  • Dietary information reported by next of kin may have been inadequate.
  • Imprecise measurement of confounders may limit how well they were controlled.

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, Case-Control Study, Relative Risk, confidence interval, Occupational Exposure, Latency.

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