Contribution of environmental factors to cancer risk

Our plain-English summary of Contribution of environmental factors to cancer risk, by P. Boffetta, F. Nyberg (British Medical Bulletin, 2003).

The study

• Authors: P. Boffetta, F. Nyberg
• Journal: British Medical Bulletin
• Published: 2003;68:71-94
• Type of article: Review
• Cited by: 168 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

Environmental carcinogens, in a strict sense, include outdoor and indoor air pollutants, as well as soil and drinking water contaminants. An increased risk of mesothelioma has consistently been detected among individuals experiencing residential exposure to asbestos, whereas results for lung cancer are less consistent. At least 14 good-quality studies have investigated lung cancer risk from outdoor air pollution based on measurement of specific agents. Their results tend to show an increased risk in the categories at highest exposure, with relative risks in the range 1.5-2.0, which is not attributable to confounders. Results for other cancers are sparse. A causal association has been established between exposure to environmental tobacco smoke and lung cancer, with a relative risk in the order of 1.2. Radon is another carcinogen present in indoor air which may be responsible for 1% of all lung cancers. In several Asian populations, an increased risk of lung cancer is present in women from indoor pollution from cooking and heating. There is strong evidence of an increased risk of bladder, skin and lung cancers following consumption of water with high arsenic contamination; results for other drinking water contaminants, including chlorination by-products, are inconclusive. A precise quantification of the burden of human cancer attributable to environmental exposure is problematic. However, despite the relatively small relative risks of cancer following exposure to environmental carcinogens, the number of cases that might be caused, assuming a causal relationship, is relatively large, as a result of the high prevalence of exposure.

In plain English

This article was a review, not a new study. The authors reviewed published research on cancer risk from environmental exposures: asbestos, outdoor air pollution, environmental tobacco smoke, indoor radon, other indoor air pollution, and drinking water contaminants such as arsenic. Where possible they estimated case numbers for the 15-country European Union. For asbestos, they tabulated studies of mesothelioma and lung cancer in people exposed through where they lived, usually near a mine or another major asbestos source. Mesothelioma risk was greatly increased in all but one study. Lung cancer results were less consistent: risk was raised in studies from South Africa and China but not in studies from Europe and North America. A meta-analysis they cited estimated a relative risk of 3.5 (95% CI 1.8–7.0) for mesothelioma and 1.1 (95% CI 0.9–1.5) for lung cancer. Assuming 5% of Europeans were exposed, the authors estimated 425 mesotheliomas a year in men and 56 in women in the EU. Assuming 1%, the estimates were 92 and 12. The authors noted that workplace or household asbestos exposure may have overlapped. They concluded that such estimates call for great caution and indicate only a likely order of magnitude.

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: Review of published epidemiological evidence on environmental (non-occupational, non-lifestyle) causes of cancer, with the authors' own estimates of attributable cases in the European Union
• Who was studied: Published studies, from various countries, of people with environmental (residential) asbestos exposure, plus studies of other environmental exposures. Burden estimates were made for the 15-country European Union as of 2003.
• Exposure: Non-occupational asbestos exposure, mostly residence near an asbestos mine or another major source. The table classed the studies by main fiber type: amphiboles, chrysotile, or unspecified and mixed. Other exposures reviewed were outdoor air pollution, environmental tobacco smoke, indoor radon, indoor cooking and heating smoke, and drinking water contaminants (arsenic, chlorination by-products, nitrates and others).
• Main results:
  • In the reviewed studies, mesothelioma risk was greatly increased among people with environmental asbestos exposure in all but one study.
  • Lung cancer results for environmental asbestos exposure were less consistent: risk was increased in studies from South Africa and China, not in studies from Europe and North America.
  • A cited meta-analysis estimated a relative risk of mesothelioma from environmental asbestos exposure of 3.5 (95% CI 1.8–7.0). For lung cancer the figure was 1.1 (95% CI 0.9–1.5).
  • Assuming 5% of the population had residential exposure, the authors estimated 425 mesotheliomas in men and 56 in women per year in the EU.
  • If a causal link to lung cancer is assumed, the 5% scenario also gave 771 lung cancers in men and 206 in women per year in the EU.
  • Under a more conservative assumption of 1% exposed, the estimates were 92 mesotheliomas in men and 12 in women per year, plus 153 lung cancers in men and 41 in women.
  • For outdoor air pollution, under the authors' conservative exposure scenario, about 3.6% of lung cancers in the EU would be attributable, some 7000 cases per year.
  • The authors estimated lung cancer cases attributable to indoor radon in Europe at about 2000 per year.
• The authors' conclusion: The authors concluded that several environmental exposures have been linked to increased cancer risk. They said their burden estimates are uncertain, call for great caution, and show only the likely order of magnitude of the risk.
• Limitations the authors state:
  • People in the reviewed asbestos studies may also have had occupational or household asbestos exposure, especially in ecological studies without individual exposure assessment.
  • Imperfect control for smoking and other lung carcinogens may explain the inconsistent lung cancer results.
  • Non-occupational asbestos exposure is hard to assess: levels are generally low, and duration, frequency and fiber type are seldom known precisely.
  • The 5% exposure prevalence used for the EU estimates may overstate the prevalence of exposures comparable to those in the reviewed studies.

Topics

Medical terms in this study, explained in our Lexicon: Mesothelioma, Lung Cancer, Relative Risk, Environmental Exposure.

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