Environmental risk factors for liver cancer and nonalcoholic fatty liver disease

Our plain-English summary of Environmental risk factors for liver cancer and nonalcoholic fatty liver disease, by T. VoPham (Current Epidemiology Reports, 2019).

The study

• Author: T. VoPham
• Journal: Current Epidemiology Reports
• Published: 2019;6(1):50-66
• Cited by: 53 articles, as counted by NIH iCite
• Read it: PubMed · Publisher · Free full text

Abstract

Purpose Of Review: The objective of this review was to summarize recent epidemiologic research examining the associations between environmental exposures and liver cancer and nonalcoholic fatty liver disease (NAFLD).

Recent Findings: There were 28 liver cancer studies showing positive associations for exposures to aflatoxin, air pollution, polycyclic aromatic hydrocarbons, asbestos, chimney sweeping occupation, and paints; an inverse association for ultraviolet radiation; and null/inconsistent results for organic solvents, pesticides, perfluorooctanoic acid, nuclear radiation, iron foundry occupation, and brick kiln pollution. There were n=5 NAFLD studies showing positive associations for heavy metals, methyl tertiary-butyl ether, and selenium; and no association with trihalomethanes.

Summary: Evidence suggests that particular environmental exposures may be associated with liver cancer and NAFLD. Future liver cancer studies should examine specific histological subtypes and assess historical environmental exposures. Future NAFLD research should examine incident, biopsy-confirmed cases and the potential role of obesity and/or diabetes in studies of environmental factors and NAFLD.

In plain English

In this narrative review, the author searched the MEDLINE database for human studies published from January 2013 to April 2018 on environmental exposures and liver cancer or nonalcoholic fatty liver disease (NAFLD). The review included 28 liver cancer studies and 5 NAFLD studies. Three of the liver cancer studies looked at occupational asbestos exposure; the review does not name fiber types. In a French cohort of 2024 asbestos-exposed workers, male workers had more liver cancer than the general population in Calvados (SIR 1.85, 95% CI 1.09–2.92); among females there was 1 case (SIR 2.55, 95% CI 0.03–14.2). Shipbreaking workers in Taiwan had higher liver cancer incidence than a matched population cohort (HR 1.50, 95% CI 1.16–1.94). An earlier, smaller study of 4155 male shipbreaking workers found no elevation compared with Taiwan's general population in an analysis with a five-year latency period (SIR 1.05, 95% CI 0.82–1.33). The author noted that the asbestos studies showing positive associations did not adjust for liver cancer risk factors and/or were limited in sample size. The author concluded that evidence suggests particular environmental exposures may be associated with liver cancer and NAFLD.

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: narrative review of epidemiologic studies (not a new study)
• Who was studied: Published human, English-language original research studies found by searching MEDLINE (via PubMed) for January 2013 to April 2018. The review included 28 liver cancer studies (3 found by citation chaining) and 5 NAFLD studies (1 found by citation chaining). The three asbestos studies covered asbestos-exposed workers in France (n = 2024, 1978–2009) and shipbreaking workers in Taiwan (1985–2008).
• Exposure: Environmental exposures, including occupational asbestos exposure (3 studies: asbestos-exposed workers in France and shipbreaking workers in Taiwan; fiber types not named), as well as aflatoxin, air pollution, polycyclic aromatic hydrocarbons, organic solvents, pesticides, perfluorooctanoic acid, iron foundry occupation, radiation, brick kiln pollution and parental occupational chemical exposures.
• Main results:
  • Reviewed study (Boulanger et al. 2015, France): compared with the general population in Calvados, asbestos-exposed male workers had an increased risk of liver cancer (SIR 1.85, 95% CI 1.09–2.92). Female workers did not have an increased risk (SIR 2.55, 95% CI 0.03–14.2). There were 18 male cases and 1 female case.
  • Reviewed study (Wu et al. 2015, Taiwan): 4427 shipbreaking workers were compared with a population-based cohort of 22,135 people matched on age, sex and place of residence. The workers had an increased risk of liver cancer (HR 1.50, 95% CI 1.16–1.94), based on 349 liver cancer cases.
  • Reviewed study (Wu et al. 2014, Taiwan): among 4155 male shipbreaking workers, liver cancer incidence was not elevated compared with the general population of Taiwan in an analysis with a five-year latency period (SIR 1.05, 95% CI 0.82–1.33), based on 72 cases.
  • Across all 28 liver cancer studies, the review reported positive associations for aflatoxin, air pollution, polycyclic aromatic hydrocarbons, asbestos, chimney sweeping occupation and paints.
• The authors' conclusion: The author concluded that evidence suggests particular environmental exposures may be associated with liver cancer and NAFLD.
• Limitations the authors state:
  • The asbestos studies that showed positive associations did not adjust for liver cancer risk factors and/or had limited sample sizes.
  • The earlier Taiwanese shipbreaking study had fewer cases than the more recent one and used the general population as its comparison group.
  • Most reviewed studies combined several kinds of liver cancer (histologies) rather than examining one type.

Topics

Medical terms in this study, explained in our Lexicon: Environmental Exposure, Histological Subtype, Biopsy.

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