Elsevier

Environmental Research

Volume 201, October 2021, 111487
Environmental Research

Effects of air pollution on health: A mapping review of systematic reviews and meta-analyses

https://doi.org/10.1016/j.envres.2021.111487Get rights and content

Abstract

Background

There has been a notable increase in knowledge production on air pollution and human health.

Objective

To analyze the state of the art on the effects of air pollution on human health through a mapping review of existing systematic reviews and meta-analyses (SRs and MAs).

Methods

The systematic mapping review was based on the recommendations for this type of scientific approach in environmental sciences. The search was performed using PubMed, Web of Science, Scopus, Cinahl, and Cochrane Library databases, from their inception through June 2020.

Results

Among 3401 studies screened, 240 SRs and MAs satisfied the inclusion criteria. Five research questions were answered. There has been an overall progressive increase in publications since 2014. The majority of the SRs and MAs were carried out by researchers from institutions in China, the US, the UK, and Italy. Most studies performed a meta-analysis (161). In general, the reviews support the association of air pollution and health outcomes, and analyzed the effects of outdoor air pollution. The most commonly investigated health outcome type was the respiratory (mainly asthma and COPD), followed by cardiovascular outcomes (mainly stroke). Particulate matter (with a diameter of 2.5 μm (PM2.5) and 10 μm (PM10) or less) and nitrogen dioxide (NO2) were the most widely investigated pollutants in the reviews. The general population was the most common sample in the reviews, followed by children, and adults. The majority of the reviews investigated health outcomes of respiratory diseases in children, as well as cardiovascular diseases in all ages. Combining health outcomes and air pollutants, PM2.5 was included in a higher number of reviews in eight health outcomes, mainly cardiovascular diseases.

Discussion

The majority of SRs and MAs showed that air pollution has harmful effects on health, with a focus on respiratory and cardiovascular outcomes. Future studies should extend the analysis to psychological and social aspects influenced by air pollution.

Introduction

Air pollution is recognized as a leading problem for public health, and a major environmental health problem around the world, deserving growing interest from the scientific community (Brunekreef, Holgate, 2002; Landrigan, 2017). The ambient air pollution may be caused by many different contaminants, although the following are the most commonly studied; particulate matter (PM), ground-level ozone (O3), carbon monoxide (CO), sulfur dioxide (SO2), and nitrogen dioxide (NO2) (Brook et al., 2004; Sheehan et al., 2016). Regarding particulate matter, the most widely used descriptors are PM2.5 and PM10, defined as the mass, in a given air volume, of all the particles with an aerodynamic diameter below 2.5 μm and 10 μm, respectively.

There is much evidence that both acute and chronic exposure to air pollution, especially coarse and fine particulates, increases the morbidity and mortality of the population (Liu et al., 2019; Sanyal et al., 2018). The World Health Organization (WHO) estimates 4.2 million deaths every year as a result of exposure to ambient (outdoor) air pollution (WHO, 2018), which makes air pollution the fourth highest-ranking risk factor for death worldwide (Brauer, 2016). It is also worth mentioning that 91% of the world's population lives in places where air quality levels exceed WHO guideline limits (WHO, 2016). According to the Lancet Report, pollution costs the global economy $4.6 trillion per year, corresponding to 6.2% of global economic output (GAHP, 2020).

A notable increase in knowledge production on air pollution and human health has recently been observed (Sun, Zhu, 2019a), through numerous studies that reported both short- and long-term effects of air pollution exposure, including several investigated health outcomes and different pollutants (Sun, Zhu, 2019a). In particular, Sun, Zhu recently detected 799 original studies focused on health outcomes caused by outdoor air pollution (2019a).

According to Sheehan et al. (2016), the last decade was marked by the increase in the use of systematic reviews and meta-analyses (SRs and MAs) techniques in environmental health epidemiology with respect to the recent past. Considering the exponential increase in systematic reviews and meta-analyses, which may be related to the increase in scientific production of original studies, there is a need to analyze these publications, to identify gaps in the literature and guide future research. As the a priori hypothesis was that there are many systematic reviews and meta-analysis dealing with the topic, a mapping review could be a better way to analyze this vast literature, instead of an umbrella review. Mapping reviews are a research tool used to map out and categorize research with the aim of identifying gaps and commissioning further reviews (Craig et al., 2017).

To the best of the authors’ knowledge, there are few studies in this sense in the environmental sciences area. A similar study was conducted by Song et al. (2017) to investigate the impact of ambient temperature on morbidity and mortality; the authors included twenty-eight studies and concluded that heat exposure seemed to have an adverse effect on mortality. Alternatively, an overview of reviews on ambient air pollution was performed by Sheehan et al. (2016) who focused on reviewing the reporting and methods practices of 43 systematic reviews and meta-analyses published from 2009 to 2015.

Therefore, there is currently no up-to-date, complete, and comprehensive analysis through a systematic summary of systematic reviews and meta-analyses about the effects of air pollution on health, focused on human health outcomes. Thus, to better understand the research evolution in the field, considering the quantity of scientific evidence already published, it is important to analyze the characteristics of the studies and the main health outcomes investigated due to exposure to different pollutants. Thus, to assimilate the vast amount of research available regarding the relationship between air pollution and health, we performed a mapping review of existing systematic reviews and meta-analyses aiming to analyze the state of the art concerning the effects of air pollution on human health.

Section snippets

Guidelines

A systematic mapping review was performed to analyze and summarize the effects of air pollution on health. The work was based on the recommendations for mapping reviews in environmental sciences by James, Randall, and Haddaway (2016).

Three filters to gather (search procedure), select (inclusion and exclusion criteria), and extract (data extraction) relevant information from the literature were applied in this mapping review (Peters, Wood, 2017). The steps described in the Template for a Mapping

Literature search results

The literature search identified 3401 relevant articles and 2199 unique citations across all sources. Of these, 283 full papers were assessed for eligibility, and 240 SRs and MAs were selected for synthesis (see Fig. 1 PRISMA flowchart).

Here, the five previously detailed research questions will be answered based on the review synthesis.

RQ1. How many SRs and MAs have been published on the effects of air pollution on health? Is there any temporal trend? What is the geographical distribution of

Discussion

This is the first systematic mapping review carried out on the effects of air pollution on health, considering only systematic reviews and meta-analysis. The current mapping review includes relevant SRs and MAs to provide a more complete picture of the work performed thus far in one of the most important fields of research. Air pollution is a major environmental risk to health and a global health concern, being one of the main causes of morbidity and mortality of the population worldwide (WHO,

Funding

This work was supported by the Research Innovation Support Foundation of the State of Santa Catarina (FAPESC) under Grant [2019031000035 and Call number 04.2018]. This study was financed in part by the Coordenação de Aperfeiçoamento de Pessoal de Nível Superior - Brasil (CAPES) – Finance Code 001.

Declaration of competing interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

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