Cancer mortality and asbestos deposits

Our plain-English summary of Cancer mortality and asbestos deposits, by T.R. Fears (American Journal of Epidemiology, 1976).

The study

• Author: T.R. Fears
• Journal: American Journal of Epidemiology
• Published: 1976;104(5):523-6
• Cited by: 8 articles, as counted by NIH iCite
• Read it: PubMed · Publisher
• In J-M's library: Johns-Manville's company medical library held a copy (J-M no. 002274).

Abstract

Asbestos deposits are found in many parts of the United States. In this paper the question is asked: Is there an increase in risk from cancer associated with naturally-occurring asbestos? In an attempt to control for the urban effect, geographic gradient and socioeconomic class, each county in the United States with asbestos deposits was matched for percent of area that was urban and for median years in school with two nearby counties that did not have known asbestos deposits. The study of cancer mortality rates in these matched counties provides no evidence that naturally-occurring asbestos is a great hazard to the general population of counties with asbestos depostis.

In plain English

This National Cancer Institute study asked whether naturally occurring asbestos deposits were linked to higher cancer death rates in the US counties containing them. A US Geological Survey listing identified 99 deposit counties (54 with amphibole, 45 with chrysotile). Two were dropped because their data were combined with other counties. Each remaining county was matched with two counties in the same or a nearby state that had no known deposits and were similar in urban area and schooling. The author compared 1950-1969 age-adjusted death rates among white men and women for cancers of the lung, esophagus, stomach, large intestine, rectum, and biliary passages and liver. Before matching, deposit counties had lower rates than the US as a whole, possibly because they were heavily rural. After matching, no statistically significant differences were found for men or women, or for chrysotile or amphibole counties. No one's actual exposure was measured, and smoking and other factors could not be accounted for. The author concluded the study gave no evidence that the deposits were a great hazard to the general population of those counties.

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 (population-level) matched-county comparison of cancer mortality rates, with paired t-tests, Wilcoxon tests and multiple regression
• Who was studied: US counties with asbestos deposits: 99 identified (54 amphibole, 45 chrysotile). Two amphibole counties were excluded, leaving 97 deposit counties and 194 matched control counties in the contiguous US. Rates for white males and white females, 1950-1969, were studied.
• Exposure: Presence of naturally occurring asbestos deposits in the county, classified as chrysotile, amphibole (including anthophyllite and tremolite), or both. No individual exposure was measured.
• Main results:
  • Before matching, cancer mortality rates in the asbestos deposit counties were substantially below US totals. The author suggested the counties' heavily rural character might explain this.
  • Asbestos deposit counties compared with their matched control counties: no significant differences (all p greater than .10) for white males or white females, for any studied cancer site.
  • No significant differences (all p greater than .10) when chrysotile counties or amphibole counties were analyzed separately against their controls.
  • Lung cancer (bronchus and lung), all asbestos counties compared with all control counties: 31.86 vs 32.59 deaths per 100,000 for white males, and 5.38 vs 5.31 for white females (Table 2).
  • Multiple regression by deposit type (amphibole, chrysotile, both) found no significant increases in cancer mortality for any site in males or females. The model explained no more than 10 per cent of the variation for any site or sex.
• The authors' conclusion: The author concluded that the study provides no evidence that naturally occurring asbestos is a great hazard to the general population of counties with asbestos deposits.
• Limitations the authors state:
  • No measurements of individual asbestos exposure were taken. The author assumed that deposits meant elevated exposure.
  • Counties were the unit of study, so population rates may not reflect risk to individuals. A few highly exposed people might not be detected.
  • Migration within the US and other sources of asbestos complicate interpretation.
  • Other causal factors such as smoking, alcohol, food, air and water could not be adjusted for.

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