A Comparative Analysis of Lung Cancer Incidence and Tobacco Consumption in Canada, Norway and Sweden: A Population-Based Study

Our plain-English summary of A Comparative Analysis of Lung Cancer Incidence and Tobacco Consumption in Canada, Norway and Sweden: A Population-Based Study, by J. Chen (International Journal of Environmental Research and Public Health, 2023).

The study

• Author: J. Chen
• Journal: International Journal of Environmental Research and Public Health
• Published: 2023;20(20)
• Cited by: 16 articles, as counted by NIH iCite
• Read it: PubMed · Publisher · Free full text

Abstract

Risk factors for developing lung cancer include tobacco smoking, exposure to second-hand smoke, radon gas, asbestos and other carcinogens, as well as air pollution and aging. Canada, Norway and Sweden are three Arctic countries that are very similar in socioeconomic status, similar in the social determinants of health and many environmental factors, including current smoking rates. However, lung cancer incidence rates differ significantly among the three countries. Since tobacco smoking is the principal risk factor for developing lung cancer, and there is a long lag time between tobacco consumption and lung cancer incidence at the population average level, a comparative analysis is conducted with historical data available publicly in the three countries to demonstrate how tobacco consumption in the past impacts lung cancer incidence decades late. The analysis shows that lung cancer incidence rates increase proportionally with the increasing tobacco consumption rates with a lag time of 20-30 years. On average, one more cigarette smoked per person per day can increase lung cancer cases by 2 to 5 per 100,000 population.

In plain English

This was an ecological study by a single author at Health Canada, using national population-average data from Canada, Norway and Sweden. It did not study asbestos. Asbestos was named only as one known lung cancer risk factor. Using public records, the author compared tobacco consumption (cigarettes per person per day, 1950s to 2000s) with age-standardized lung cancer incidence rates (1960s to 2020) and looked for the time lag between the two. In Canada, the highest correlation was 0.95 at a 21-year lag for men and 0.90 at a 29-year lag for women. The best-estimated lags were 17 and 31 years in Norway, and 13 and 32 years in Sweden. On average, one more cigarette per person per day went with 3.4 plus or minus 1.3 more lung cancer cases per 100,000. The country figures ranged from 1.96 for Canadian women to 5.40 for Norwegian women. The author concluded that incidence rises proportionally with past tobacco consumption. The author noted large uncertainties in smoking survey data and that individual-level data were not available.

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: Ecological study comparing national population-average historical data (described by the author as a comparative, population-based analysis)
• Who was studied: National populations of Canada, Norway and Sweden. Lung cancer incidence came from the IARC database for Norway and Sweden (1960 to 2020) and for Canada (1983 to 2020), with Canadian data for 1969 to 1982 from Canadian Cancer Statistics 1997. Tobacco data covered adults aged 15 and older.
• Exposure: Population-average tobacco consumption, measured as cigarettes per person per day, from the 1950s to the 2000s. Asbestos exposure was not studied.
• Main results:
  • Canada: the highest correlation between tobacco consumption and lung cancer incidence was 0.95 at a 21-year lag for men, and 0.90 at a 29-year lag for women.
  • Norway: the best-estimated lag was 17 years for males and 31 years for females.
  • Sweden: the best-estimated lag was 13 years for males and 32 years for females.
  • Increase in lung cancer incidence per 100,000 for each extra cigarette per person per day was 3.85 for Canadian men and 1.96 for Canadian women, 3.66 for Norwegian men and 5.40 for Norwegian women, and 2.42 for Swedish men and 3.03 for Swedish women. The overall average was 3.4 plus or minus 1.3 per 100,000.
  • Lung cancer incidence correlated with tobacco consumption with R-squared of 0.80 or higher.
  • For women around 2010 (averaged 2008 to 2012), lung cancer incidence was 31 per 100,000 in Canada, 26 in Norway and 19 in Sweden. Average tobacco consumption from 1981 to 2005 was 5.7, 4.4 and 3.5 cigarettes per person per day in those countries.
  • Among Canadian men, a 36% reduction in tobacco smoking was followed about 21 years later by about a 37% reduction in lung cancer cases.
• The authors' conclusion: The author concluded that, at the population average level, age-standardized incidence of all types of lung cancer increases proportionally with population-average tobacco consumption, and that smoking affects incidence for decades even after smoking rates drop. The author stated that one more cigarette per person per day can increase lung cancer cases by 2 to 5 per 100,000.
• Limitations the authors state:
  • Reported annual tobacco consumption rates come from surveys of varying sample size, and cigarette products changed over time, so they carry large uncertainties.
  • Reported lung cancer incidence rates also carry statistical uncertainties, but to a lower degree.
  • Individual-level data were not publicly available, so the study used only national population averages. The lag time may vary with factors such as tobacco products, age at starting smoking, smoking duration and lung cancer type.
  • The difference in women's lung cancer incidence between Norway and Sweden could not be explained by 15-year averaged tobacco consumption, which was the same in both countries.

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, Incidence.

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