Environmental and ecological factors of stomach cancer incidence and mortality: a systematic review study on ecological studies

Our plain-English summary of Environmental and ecological factors of stomach cancer incidence and mortality: a systematic review study on ecological studies, by S. Khazaei, A. Mohammadbeigi, E. Jenabi, et al (Reviews on Environmental Health, 2020).

The study

• Authors: S. Khazaei, A. Mohammadbeigi, E. Jenabi, A. Asgarian, H. Heidari, A. Saghafipour, S. Arsang-Jang, H. Ansari
• Journal: Reviews on Environmental Health
• Published: 2020;35(4):443-452
• Type of article: Systematic review
• Cited by: 8 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

Objectives: Stomach cancer (SC) is one of the most common and deadly types of cancer. It is the third leading cause of cancer deaths worldwide. The effect of environmental and ecological factors in SC have been assessed in some studies. Thus, we aimed to synthesize the environmental and ecological factors of SC incidence and mortality.

Content: In this systematic review study, the scientific databases, including Web of Science, Scopus and PubMed, were searched from inception to November 2019 for all primary articles written in English by using relevant Medical Subject Heading (Mesh) terms. Two independent authors conducted the screening process to decide on the eligibility and inclusion of the articles in the study. The third author acted as an arbiter to resolve any disagreements.

Summary And Outlook: A total of 157 potentially relevant articles were identified from the initial search 38 of which met the eligibility criteria; finally, 34 articles were included in the systematic review. The results revealed that soil arsenic exposure, coal and other opencast mining installations, living near incinerators and installations for the recovery or disposal of hazardous waste, installations for the production of cement, lime, plaster, and magnesium oxide, proximity to a metal industry sources, dietary iron, ingested asbestos, farming, arsenic in soil, altitude, organochlorines and environmental exposure to cadmium and lead have positive associations with SC incidence or death. Most of the ecological and environmental factors such as living near the mineral industries, the disposal of hazardous waste, metal industry sources and environmental exposure to cadmium and lead are positively related to SC mortality and incidence. However, solar UV-B, heat index and dietary zinc can be taken into account as protective factors against SC mortality and incidence.

© 2020 Walter de Gruyter GmbH, Berlin/Boston.

In plain English

This article was a systematic review. The authors searched three databases up to November 2019 for English-language ecological studies linking environmental factors to stomach cancer. Ecological studies compare disease rates between areas or populations rather than individuals. Of 157 articles found, 34 published between 1995 and 2019 were included: eight from America, 10 from Asia and 16 from Europe. Asbestos appeared in only one of them, a Norwegian study of lighthouse keepers exposed to asbestos in drinking water. The review reported that this study found a positive correlation between ingested asbestos and gastrointestinal cancer in general and stomach cancer specifically. The review gave no figures for it. Other factors listed as positively correlated included soil arsenic, mining, hazardous waste installations, the metal industry, cadmium and lead. Solar UV-B, heat index and dietary zinc were negatively correlated. The authors concluded that most of these environmental factors were positively related to stomach cancer incidence and mortality. They noted that ecological studies are open to ecological fallacy, to effects of how areas are defined, and to unmeasured confounding, such as differences in Helicobacter pylori infection.

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: Systematic review of ecological (population-level) studies; no new data were collected
• Who was studied: 34 ecological studies published between 1995 and 2019: eight from America, 10 from Asian countries and 16 from Europe (seven of them from Spain)
• Exposure: A range of environmental and ecological factors, including ingested asbestos (asbestos in drinking water, in one Norwegian study of lighthouse keepers), soil arsenic, mining, industrial installations, hazardous waste, metals, nitrate, radon, solar UV-B, altitude, latitude and farming
• Main results:
  • Of 157 articles identified, 34 were included in the review
  • One included study (Kjaerheim et al., Norway, lighthouse keepers) was reported as showing a positive correlation between ingested asbestos and gastrointestinal cancer risk in general and stomach cancer risk specifically; no numbers were given in the review
  • Factors reported as positively correlated with stomach cancer incidence and mortality included soil arsenic, mining, incinerators and hazardous waste installations, cement and lime installations, metal industry, dietary iron, ingested asbestos, altitude, farming, organochlorines, cadmium and lead
  • Methyl mercury (MeHg), solar UV-B, heat index and dietary zinc were negatively correlated with stomach cancer mortality and incidence
  • Six studies reported a negative correlation between solar UV-B and gastric cancer
  • Results for urbanization, nitrate in drinking water and latitude were contradictory
  • Correlations of pesticide sales and of hexavalent chromium in drinking water and soil with stomach cancer incidence or death were not statistically significant
• The authors' conclusion: The authors concluded that most of the ecological and environmental factors studied, including ingested asbestos, were positively related to stomach cancer mortality and incidence. They concluded that MeHg, solar UV-B, heat index and dietary zinc were protective.
• Limitations the authors state:
  • Results of ecological studies are subject to ecological fallacy, the modifiable areal unit problem and unmeasured confounding
  • Findings at the population level may not apply to individuals
  • Associations may be confounded by unmeasured factors such as differences in Helicobacter pylori infection

Topics

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

Medical terms in this study, explained in our Lexicon: Stomach Cancer, Systematic Review, Environmental Exposure.

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• Exposure to nitrosamines, carbon black, asbestos, and talc and mortality from stomach, lung, and laryngeal cancer in a cohort of rubber workers — K. Straif, U. Keil, et al. (2000)
• Stomach cancer mortality among workers exposed to asbestos: a meta-analysis — W.J. Peng, X.J. Jia, et al. (2015)

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