Environmental Risk Factors and Health: An Umbrella Review of Meta-Analyses

Abstract

Environmental Risk Factors and Health: An Umbrella Review of Meta-Analyses Rojas-Rueda D, Morales-Zamora E, Alsufyani WA, Herbst CH, AlBalawi SM, Alsukait R, Alomran M. Environmental Risk Factors and Health: An Umbrella Review of Meta-Analyses. International Journal of Environmental Research and Public Health. 2021; 18(2):704. Abstract Background: Environmental health is a growing area of knowledge, continually increasing and updating the body of evidence linking the environment to human health. Aim: This study summarizes the epidemiological evidence on environmental risk factors from meta-analyses through an umbrella review. Methods: An umbrella review was conducted on meta-analyses of cohort, case-control, case-crossover, and time-series studies that evaluated the associations between environmental risk factors and health outcomes defined as incidence, prevalence, and mortality. The specific search strategy was designed in PubMed using free text and Medical Subject Headings (MeSH) terms related to risk factors, environment, health outcomes, observational studies, and meta-analysis. The search was limited to English, Spanish, and French published articles and studies on humans. The search was conducted on September 20, 2020. Risk factors were defined as any attribute, characteristic, or exposure of an individual that increases the likelihood of developing a disease or death. The environment was defined as the external elements and conditions that surround, influence, and affect a human organism or population’s life and development. The environment definition included the physical environment such as nature, built environment, or pollution, but not the social environment. We excluded occupational exposures, microorganisms, water, sanitation and hygiene (WASH), behavioral risk factors, and no- natural disasters. Results: This umbrella review found 197 associations among 69 environmental exposures and 83 diseases and death causes reported in 103 publications. The environmental factors found in this review were air pollution, environmental tobacco smoke, heavy metals, chemicals, ambient temperature, noise, radiation, and urban residential surroundings. Among these, we identified 65 environmental exposures defined as risk factors and 4 environmental protective factors. In terms of study design, 57 included cohort and/or case-control studies, and 46 included time-series and/or case-crossover studies. In terms of the study population, 21 included children, and the rest included adult population and both sexes. In this review, the largest body of evidence was found in air pollution (91 associations among 14 air pollution definitions and 34 diseases and mortality diagnoses), followed by environmental tobacco smoke with 24 associations. Chemicals (including pesticides) were the third larger group of environmental exposures found among the meta-analyses included, with 19 associations. Conclusion: Environmental exposures are an important health determinant. This review provides an overview of an evolving research area and should be used as a complementary tool to understand the connections between the environment and human health. The evidence presented by this review should help to design public health interventions and the implementation of health in all policies approach aiming to improve population health. Excerpts Table 13: mdpi.com Radon, a radioactive natural, was found in a recent meta-analysis as a risk factor for lung cancer [100] at indoor radon exposure levels above 100 Bq/m3 (Table 13). In another meta-analysis, indoor radon exposure was also associated as a risk factor for childhood leukemia [101]. Finally, long-term exposures to extremely low-frequency electromagnetic fields were also found associated as a risk factor for amyotrophic lateral sclerosis [67] and childhood leukemia [99] (Table 13). Extremely low-frequency (ELF) magnetic fields are alternating fields generated by the distribution and supply of electricity. Although this umbrella review found several publications and associations among environmental exposures and health outcomes, we also identified several evidence gaps. Most of the studies focus on identifying environmental risk factors, and only a few studies have been focusing on identifying environmental protective factors. Furthermore, few studies have focused on vulnerable and disadvantaged populations (children, elders, social disadvantaged, ethnic minorities, etc.). Furthermore, most studies do not provide a clear definition of the health outcomes using the international classification of diseases (ICD), nor a comparable exposure definition when the same pollutant is used. In terms of the meta-analysis, we exclude several studies from this review because, in the analyses, cross-sectional studies were mixed with other observational studies (i.e., cohorts). Additionally, several studies did not report heterogeneity values (i.e., I2) or do not provide dose-response functions essential for population risk assessment, health impact assessments and policy translation. We have summarized a list of recommendations for future research in environmental health studies based on these gaps, and we have listed those recommendations in Table 16. Open access paper: mdpi.com

AI evidence extraction

Main findings

This umbrella review of meta-analyses reports that long-term exposure to extremely low-frequency (ELF) electromagnetic fields was found associated as a risk factor for amyotrophic lateral sclerosis and childhood leukemia in included meta-analyses. It also reports indoor radon exposure above 100 Bq/m3 as a risk factor for lung cancer and an association with childhood leukemia in other meta-analyses. The review summarizes 197 associations across 69 environmental exposures and 83 diseases/death causes from 103 publications.

Outcomes measured

• Amyotrophic lateral sclerosis (ALS)
• Childhood leukemia
• Lung cancer (radon)

Limitations

• Umbrella review summarizes existing meta-analyses and does not provide new primary data.
• The abstract notes evidence gaps, including limited focus on protective factors and vulnerable/disadvantaged populations.
• Many included studies/meta-analyses reportedly lacked clear, comparable exposure definitions and clear outcome definitions (e.g., ICD coding).
• Some meta-analyses did not report heterogeneity (e.g., I2) or dose-response functions, limiting risk assessment and policy translation.
• The review excluded meta-analyses that mixed cross-sectional studies with other observational designs, potentially affecting coverage of the literature.

Suggested hubs

• power-lines (0.78)
  Mentions long-term extremely low-frequency (ELF) magnetic fields generated by electricity distribution/supply and associations with ALS and childhood leukemia.

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    "study_type": "systematic_review",
    "exposure": {
        "band": "ELF",
        "source": "power distribution and supply of electricity",
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        "sar_wkg": null,
        "duration": "long-term"
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    "population": "Humans (children and adults; both sexes)",
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    "outcomes": [
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    "effect_direction": "harm",
    "limitations": [
        "Umbrella review summarizes existing meta-analyses and does not provide new primary data.",
        "The abstract notes evidence gaps, including limited focus on protective factors and vulnerable/disadvantaged populations.",
        "Many included studies/meta-analyses reportedly lacked clear, comparable exposure definitions and clear outcome definitions (e.g., ICD coding).",
        "Some meta-analyses did not report heterogeneity (e.g., I2) or dose-response functions, limiting risk assessment and policy translation.",
        "The review excluded meta-analyses that mixed cross-sectional studies with other observational designs, potentially affecting coverage of the literature."
    ],
    "evidence_strength": "high",
    "confidence": 0.7199999999999999733546474089962430298328399658203125,
    "peer_reviewed_likely": "yes",
    "stance": "concern",
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    "summary": "This umbrella review summarizes epidemiological evidence from meta-analyses of observational studies on environmental risk factors and health outcomes in humans. It reports that included meta-analyses found long-term extremely low-frequency (ELF) electromagnetic field exposure associated with amyotrophic lateral sclerosis and childhood leukemia. The review also highlights multiple evidence gaps, including inconsistent exposure/outcome definitions and incomplete reporting of heterogeneity and dose-response information.",
    "key_points": [
        "Umbrella review of meta-analyses covering cohort, case-control, case-crossover, and time-series evidence in humans.",
        "Across 103 publications, the review reports 197 associations among 69 environmental exposures and 83 diseases/death causes.",
        "Radiation-related findings mentioned include indoor radon (above 100 Bq/m3) as a risk factor for lung cancer and an association with childhood leukemia.",
        "Included meta-analyses are reported to find long-term ELF electromagnetic field exposure associated with ALS and childhood leukemia.",
        "ELF magnetic fields are described as alternating fields generated by electricity distribution and supply.",
        "The authors note major evidence gaps, including inconsistent exposure definitions and limited reporting of heterogeneity and dose-response functions."
    ],
    "categories": [
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        "Extremely Low Frequency (ELF)",
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        "childhood leukemia",
        "amyotrophic lateral sclerosis",
        "ALS"
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            "reason": "Mentions long-term extremely low-frequency (ELF) magnetic fields generated by electricity distribution/supply and associations with ALS and childhood leukemia."
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    "social": {
        "tweet": "Umbrella review (IJERPH, 2021) of meta-analyses on environmental risk factors reports associations for many exposures; it notes included meta-analyses found long-term ELF magnetic field exposure associated with ALS and childhood leukemia, and indoor radon linked with lung cancer.",
        "facebook": "A 2021 umbrella review in IJERPH summarized meta-analyses on environmental risk factors and health. It reports that included meta-analyses found long-term extremely low-frequency (ELF) magnetic field exposure associated with ALS and childhood leukemia, and indoor radon exposure linked with lung cancer, while also highlighting evidence gaps like inconsistent exposure definitions and limited dose-response reporting.",
        "linkedin": "Umbrella review (IJERPH, 2021) synthesizing meta-analyses of observational studies on environmental exposures and health outcomes. Among radiation-related findings, the authors report that included meta-analyses found long-term ELF magnetic field exposure associated with ALS and childhood leukemia, and indoor radon exposure associated with lung cancer, alongside notable gaps in exposure/outcome definitions and reporting of heterogeneity and dose-response."
    }
}

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