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 reported 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 (as reported in included meta-analyses).

Outcomes measured

• Amyotrophic lateral sclerosis (ALS)
• Childhood leukemia
• Lung cancer (radon-related, mentioned in excerpts)

Limitations

• Umbrella review summarizes associations from included meta-analyses; details of individual exposure metrics and effect sizes are not provided in the abstract/excerpts.
• Occupational exposures were excluded; findings pertain to non-occupational environmental exposures as defined by the authors.
• The review notes evidence gaps including inconsistent outcome definitions (e.g., lack of clear ICD definitions), limited comparable exposure definitions, and incomplete reporting of heterogeneity (I2) and dose-response functions in included meta-analyses.

Suggested hubs

• who-icnirp (0.28)
  Addresses environmental radiation/ELF EMF as a health risk factor within a broad evidence synthesis context relevant to guideline discussions.

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    "population": "Humans (umbrella review includes children and adults; 21 meta-analyses included children)",
    "sample_size": null,
    "outcomes": [
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