Fiber burden and asbestos-related diseases: an umbrella review

Our plain-English summary of Fiber burden and asbestos-related diseases: an umbrella review, by J.M. Ramada Rodilla, B. Calvo Cerrada, C. Serra Pujadas, et al (Gaceta Sanitaria, 2022).

The study

• Authors: J.M. Ramada Rodilla, B. Calvo Cerrada, C. Serra Pujadas, G.L. Delclos, F.G. Benavides
• Journal: Gaceta Sanitaria
• Published: 2022;36(2):173-183
• Type of article: Systematic review
• Cited by: 14 articles, as counted by NIH iCite
• Read it: PubMed · Publisher · Free full text

Abstract

Objective: What are the levels of asbestos exposure that cause each type of health effect? The objective of this study was to review the available scientific evidence on exposure levels for asbestos and their relationship to health effects.

Method: An umbrella review of English-language reviews and meta-analyses, from 1980 to March 2021 was conducted. We included reviews involving quantified asbestos exposures and health outcomes. The review has been adapted to the indications of the PRISMA declaration. Methodological quality of the selected studies was assessed using the AMSTAR instrument.

Results: We retrieved 196 references. After applying the search strategy and quality analysis, 10 reviews were selected for in-depth analysis. For lung cancer, the highest risk was observed with exposure to amphiboles. Longer, thinner fibers had the greatest capacity to cause lung cancer, especially those > 10 μm in length. For mesothelioma, longer and thinner fibers were also more pathogenic; amphiboles ≥ 5 μm are especially associated with increased mesothelioma risk. No studies observed an increased risk for lung cancer or mesothelioma at asbestos exposure levels <0.1 f/ml. No reviews provided information on exposure concentrations for pulmonary fibrosis. Currently, there is limited evidence in humans to establish the causal relationship between gastrointestinal cancer and asbestos exposure.

Conclusions: Banning all asbestos exposure remains the best measure to preventing its negative health effects. The highest quality reviews and meta-analyses support that there is little risk of lung cancer or mesothelioma at daily exposure levels below 0.1 f/ml.

Copyright © 2021 SESPAS. Publicado por Elsevier España, S.L.U. All rights reserved.

In plain English

This article was an umbrella review, which is a review of earlier systematic reviews and meta-analyses. The authors analyzed 10 such reviews, published between 1997 and 2017, that linked quantified asbestos exposure to disease. One was based on animal experiments. In these reviews, chrysotile's effect on lung cancer was weaker than that of amphibole or mixed fibers. Fibers longer than 10 micrometers were more damaging, and thinner fibers had a greater capacity to cause lung cancer. For pleural mesothelioma, exposure-response results were somewhat inconsistent. One review put the expected mesothelioma mortality risk from chrysotile, amosite and crocidolite in the proportion 1:100:500. The animal review linked fibers longer than 5 micrometers with pulmonary fibrosis (asbestosis). One review found the association with gastrointestinal cancer absent or very low; associations appeared only at very high exposures, for gastric cancer and for colon cancer. None of the reviews gave exposure levels for laryngeal or ovarian cancer. Taking the reviews together, the authors concluded there was little risk of lung cancer or mesothelioma at daily exposure levels below 0.1 fibers per milliliter. They also stated that banning and eradicating asbestos is the best preventive measure.

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: Umbrella review (review of systematic reviews and meta-analyses), with methodological quality assessed using the AMSTAR instrument
• Who was studied: 10 English-language systematic reviews and meta-analyses (searched 1980 to March 2021; those included were published 1997 to 2017), covering human studies and, in one review, experimental animal studies
• Exposure: Quantified asbestos exposure (fiber concentration, cumulative exposure, dose-response) for chrysotile, amphiboles (crocidolite, amosite, tremolite) and mixed fibers, including fiber length and thickness
• Main results:
  • On AMSTAR quality scoring of the 10 included reviews, two scored 10, one scored 8 and the rest scored from four to six
  • Lung cancer: the effect of chrysotile was weaker than that of amphibole or mixed fibers
  • Lung cancer: in one included meta-analysis (Berman et al., 2008), fibers longer than 10 micrometers were more damaging
  • Lung cancer: thinner fibers had a higher capacity to cause lung cancer
  • Lung cancer: in one included study, exposure to amosite for 2 or more years gave an SMR of 11.7, compared with an SMR of 2.64 for exposure of less than one month
  • One included review (Pierce et al.) concluded that the highest cumulative chrysotile exposure without a lung cancer effect was 25 f/ml-y
  • The same review (Pierce et al.) gave 15 f/ml-y as the highest cumulative chrysotile exposure without a mesothelioma effect
  • Pleural mesothelioma: the exposure-response results of the different studies were somewhat inconsistent
  • Pleural mesothelioma: in one review (Hodgson and Darnton), the expected mortality risk for chrysotile, amosite and crocidolite was in the proportion 1:100:500
  • Pleural mesothelioma: amphiboles 5 micrometers or longer were associated with increased mesothelioma relative risk and odds ratio
  • In the one review of non-occupational exposure (Marsh et al.), the meta-relative risk for amphibole fibers was 2.5 to 3.2 times greater than for mixed fibers and 5.3 to 5.6 times greater than for pure chrysotile
  • The meta-analysis with the highest methodological quality concluded that little risk of mesothelioma would be observed with asbestos exposure below 0.1 f/ml
  • Pulmonary fibrosis: the review of experimental animal studies (Roggli) associated fibers longer than 5 micrometers with pulmonary fibrosis (asbestosis)
  • Gastrointestinal cancer: one review (Gamble) found the association with asbestos exposure absent or very low, with RR, OR and SMR around 1
  • Gastric cancer: in the same review, an association was observed only with very high exposures
  • Colon cancer: in the same review, among chrysotile-exposed groups, an association was found at exposures above 140 f/ml-y, with SMR = 2.31 (95% CI 1.19-4.04)
  • The included reviews gave no information on exposure levels for laryngeal or ovarian cancer
  • From the reviews taken together, the authors concluded that there is little risk of lung cancer or mesothelioma at daily exposure levels below 0.1 f/ml
• The authors' conclusion: The authors concluded that, following ILO and WHO recommendations, the best measure to prevent the health effects of asbestos is banning and eradicating it, following strict cleaning protocols. This was alongside their finding of little risk of lung cancer or mesothelioma below 0.1 f/ml daily exposure.
• Limitations the authors state:
  • Unpublished studies may have been overlooked (publication bias)
  • Exposure measures are often reconstructions made decades after the exposure, which can carry a large margin of error when applied to individual patients

Topics

The National Library of Medicine indexes this study under subjects our site covers: Lung cancer, Mesothelioma.

Medical terms in this study, explained in our Lexicon: Fiber Burden, Asbestos Exposure, Lung Cancer, Amphibole Group, Mesothelioma, Pulmonary Fibrosis.

Related studies

• Fiber burden and patterns of asbestos-related disease in chrysotile miners and millers — A. Churg, J.L. Wright, et al. (1993)
• Fiber burden and patterns of asbestos-related disease in workers with heavy mixed amosite and chrysotile exposure — A. Churg, S. Vedal (1994)
• Fiber burden and asbestos-related lung disease: determinants of dose-response relationships — M.R. Becklake, B.W. Case (1994)
• Fiber counting and analysis in the diagnosis of asbestos-related disease — A. Churg (1982)
• Human disease consequences of fiber exposures: a review of human lung pathology and fiber burden data — V.L. Roggli (1990)
• WHO/ILO work-related burden of disease and injury: Protocol for systematic reviews of occupational exposure to dusts and/or fibres and of the effect of occupational exposure to dusts and/or fibres on pneumoconiosis — D. Mandrioli, V. Schlünssen, et al. (2018)

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