Cancer of the gastrointestinal tract and exposure to asbestos in drinking water among lighthouse keepers (Norway)

Our plain-English summary of Cancer of the gastrointestinal tract and exposure to asbestos in drinking water among lighthouse keepers (Norway), by K. Kjaerheim, B. Ulvestad, J.I. Martinsen, et al (Cancer Causes & Control, 2005).

The study

• Authors: K. Kjaerheim, B. Ulvestad, J.I. Martinsen, A. Andersen
• Journal: Cancer Causes & Control
• Published: 2005;16(5):593-8
• Cited by: 37 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

Objective: Previous studies of predominantly ecological design have indicated a possible elevation of gastrointestinal cancer risk in population groups exposed to drinking water contaminated with asbestos from natural sources or asbestos-cement containing water pipes. In the present study the possible effect of ingested asbestos fibers on gastrointestinal cancer risk was investigated in an occupational group where a proportion of the employees was exposed to asbestos in their drinking water.

Method: A cohort of 726 lighthouse keepers first employed between 1917 and 1967 were followed up for cancer incidence from 1960 to 2002. The standardized incidence ratio (SIR) was calculated as the number of new cancer cases divided by the expected number based on five-year age and sex specific incidence rates in the general rural population of Norway. A 95% confidence interval (CI) was calculated for all SIR values assuming a Poisson distribution of the cancer cases.

Results: Risk of stomach cancer was elevated in the whole cohort (SIR: 1.6, CI: 1.0-2.3), in the subgroup with definite asbestos exposure (SIR: 2.5, CI: 0.9-5.5), and when the group was followed for 20 years and more after first possible exposure (SIR: 1.7, CI: 1.1-2.7). Less consistent results were found for colon cancer; SIR was 1.5 (CI: 0.9-2.2) overall, 0.8 (CI: 0.1-2.9) among the exposed, and 1.6 (CI: 1.0-2.5) twenty years and more after first possible exposure.

Conclusion: The results support the hypothesis of an association between ingested asbestos and gastrointestinal cancer risk in general and stomach cancer risk specifically.

In plain English

This Norwegian cohort study followed 726 male lighthouse keepers for cancer from 1960 to 2002. After World War II, many lighthouses got asbestos-cement roofs, mostly chrysotile with some amphibole, and some keepers drank rainwater collected from them. Cistern water tested in 1983 contained 1.8 × 10^9 to 7.1 × 10^10 fibers per liter. Cancer counts were compared with rural Norwegian male rates. The cohort had 27 stomach cancers against 17.4 expected (SIR 1.6, 95% CI 1.0–2.3), which the authors called borderline significant. Among 107 keepers classed as certainly exposed, the stomach cancer SIR was 2.5 (95% CI 0.9–5.5; six cases), not statistically significant. Twenty or more years after first possible exposure, the cohort's stomach cancer SIR was 1.7 (95% CI 1.1–2.7). Colon cancer results were less consistent. No peritoneal mesothelioma was found. The authors concluded that the results support the hypothesis of an association between ingested asbestos and gastrointestinal cancer, and stomach cancer specifically. They added that this limited excess risk does not indicate a major general-population health problem. They noted the small cohort and exposure classification problems.

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: Retrospective cohort study of cancer incidence, comparing observed cancer cases with the number expected from rates in the rural male population of Norway (standardized incidence ratios, SIR)
• Who was studied: 726 male lighthouse keepers in Norway, born after 1884, first employed between 1917 and 1966, and alive in 1960. They were followed for cancer from 1960 to 2002, a total of 17,923 person years. By exposure status: 107 exposed, 479 unexposed, 140 unknown.
• Exposure: Drinking water from cisterns that collected rainwater from asbestos-cement roof tiles installed after World War II. The tiles were about 15% asbestos, of which 92% was chrysotile, with a small amount of amphibole (anthophyllite, amosite, or crocidolite). Of 81 manned lighthouses surveyed, 21 had such water. Tap water from seven cisterns, tested in 1983, contained 1.8 × 10^9 to 7.1 × 10^10 fibers per liter. Keepers who had worked at one of the 21 lighthouses (107) were classed as 'certainly exposed'; those at other lighthouses (479) as 'possibly unexposed'; and 140 with no known workplace as unknown exposure. 1948 was taken as the start of possible exposure.
• Main results:
  • Whole cohort, all cancers: 200 new cases observed versus 186.1 expected, SIR 1.1 (95% CI 0.9–1.2)
  • Whole cohort, stomach cancer: 27 observed versus 17.4 expected, SIR 1.6 (95% CI 1.0–2.3), described as bordering on statistical significance
  • Whole cohort, gastrointestinal cancers combined (stomach, small intestine, colon, rectum): SIR 1.4 (95% CI 1.1–1.8)
  • No case of peritoneal mesothelioma was found in the cohort
  • Exposed group (107 keepers), stomach cancer: SIR 2.5 (95% CI 0.9–5.5), based on six cases (2.4 expected). The authors described this as a non-significantly elevated risk.
  • Colon cancer: overall SIR 1.5 (95% CI 0.9–2.2; 23 observed versus 15.5 expected). In the exposed group the SIR was 0.8 (95% CI 0.1–2.9; 2 cases). The SIR was highest and significantly elevated in the unknown-exposure group: 2.7 (95% CI 1.2–5.1; 9 cases).
  • Gastrointestinal cancers combined: SIR 1.5 (95% CI 0.7–2.8) in the exposed group and 2.0 (95% CI 1.2–3.1) in the unknown-exposure group
  • Whole cohort, 20 or more years after first possible exposure: stomach cancer SIR 1.7 (95% CI 1.1–2.7; 21 observed versus 12.1 expected) and colon cancer SIR 1.6 (95% CI 1.0–2.5)
  • Whole cohort, gastrointestinal cancers combined after 20 or more years: SIR 1.6 (95% CI 1.2–2.1 in the text; the table gives 1.3–2.1)
  • Small intestine cancer: 2 cases versus 0.6 expected in the whole cohort, both occurring 20 or more years after first possible exposure
  • Exposed group: no pancreatic cancer occurred. Kidney cancer SIR was 2.1 (95% CI 0.3–7.6), based on two cases only.
• The authors' conclusion: The authors concluded that the results support the hypothesis of an association between ingested asbestos and gastrointestinal cancer risk, and stomach cancer specifically. They added that the limited excess risk in this heavily exposed group does not indicate that asbestos in drinking water is a major health problem in the general population.
• Limitations the authors state:
  • Exposure classification was difficult because there was limited information on transfers between lighthouses. The 'unexposed' group may include exposed persons, possibly overestimating risk in that group.
  • The cohort was small, which the authors say is partly compensated for by the long follow-up
  • Confounding by dietary or socioeconomic factors cannot be totally ruled out for the comparison with the general rural population
  • Colon cancer results were less consistent than stomach cancer results, and the authors state that no conclusions should be drawn for colon cancer

Topics

Medical terms in this study, explained in our Lexicon: Asbestos-Cement, Standardized Incidence Ratio (SIR), Incidence, confidence interval, Stomach Cancer, Asbestos Exposure, Colorectal Cancer.

Related studies

• Incidence of cancer among lighthouse keepers exposed to asbestos in drinking water — A. Andersen, E. Glattre, et al. (1993)
• Drinking water and cancer — R.D. Morris (1995)
• Cancer incidence and asbestos in drinking water, Town of Woodstock, New York, 1980-1998 — M.L. Browne, D. Varadarajulu, et al. (2005)
• Asbestos-contaminated drinking water: its impact on household air — J.S. Webber, S. Syrotynski, et al. (1988)
• Asbestos ingestion and gastrointestinal cancer: a possible underestimated hazard — A. Di Ciaula (2017)
• Is there a risk to health in using asbestos--cement pipes for the carriage of drinking water? — S.F. McCullagh (1980)

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