Long-term PM2.5 exposure and various health outcomes: An umbrella review of systematic reviews and meta-analyses of observational studies

Choices of morbidity outcomes and concentration-response functions for health risk assessment of long-term exposure to air pollution

Background

Air pollution health risk assessment (HRA) has been typically conducted for all causes and cause-specific mortality based on concentration-response functions (CRFs) from meta-analyses that synthesize the evidence on air pollution health effects. There is a need for a similar systematic approach for HRA for morbidity outcomes, which have often been omitted from HRA of air pollution, thus underestimating the full air pollution burden. We aimed to compile from the existing systematic reviews and meta-analyses CRFs for the incidence of several diseases that could be applied in HRA. To achieve this goal, we have developed a comprehensive strategy for the appraisal of the systematic reviews and meta-analyses that examine the relationship between long-term exposure to particulate matter with an aerodynamic diameter smaller than 2.5 µm (PM2.5), nitrogen dioxide (NO2), or ozone (O3) and incidence of various diseases.

Methods

To establish the basis for our evaluation, we considered the causality determinations provided by the US Environmental Protection Agency Integrated Science Assessment for PM2.5, NO2, and O3. We developed a list of pollutant/outcome pairs based on these assessments and the evidence of a causal relationship between air pollutants and specific health outcomes. We conducted a comprehensive literature search using two databases and identified 75 relevant systematic reviews and meta-analyses for PM2.5 and NO2. We found no relevant reviews for long-term exposure to ozone. We evaluated the reliability of these studies using an adaptation of the AMSTAR 2 tool, which assesses various characteristics of the reviews, such as literature search, data extraction, statistical analysis, and bias evaluation. The tool's adaptation focused on issues relevant to studies on the health effects of air pollution. Based on our assessment, we selected reviews that could be credible sources of CRF for HRA. We also assessed the confidence in the findings of the selected systematic reviews and meta-analyses as the sources of CRF for HRA. We developed specific criteria for the evaluation, considering factors such as the number of included studies, their geographical distribution, heterogeneity of study results, the statistical significance and precision of the pooled risk estimate in the meta-analysis, and consistency with more recent studies. Based on our assessment, we classified the outcomes into three lists: list A (a reliable quantification of health effects is possible in an HRA), list B+ (HRA is possible, but there is greater uncertainty around the reliability of the CRF compared to those included on list A), and list B- (HRA is not recommended because of the substantial uncertainty of the CRF).

Results

In our final evaluation, list A includes six CRFs for PM2.5 (asthma in children, chronic obstructive pulmonary disease, ischemic heart disease events, stroke, hypertension, and lung cancer) and three outcomes for NO2 (asthma in children and in adults, and acute lower respiratory infections in children). Three additional outcomes (diabetes, dementia, and autism spectrum disorders) for PM2.5 were included in list B+. Recommended CRFs are related to the incidence (onset) of the diseases. The International Classification of Diseases, 10th revision codes, age ranges, and suggested concentration ranges are also specified to ensure consistency and applicability in an HRA. No specific suggestions were given for ozone because of the lack of relevant systematic reviews.

Conclusion

The suggestions formulated in this study, including CRFs selected from the available systematic reviews, can assist in conducting reliable HRAs and contribute to evidence-based decision-making in public health and environmental policy. Future research should continue to update and refine these suggestions as new evidence becomes available and methodologies evolve.

Spatial variability of pollution source contributions during two (2012-2013 and 2018-2019) sampling campaigns at ten sites in Los Angeles basin

This study assessed the spatial variability of PM2.5 source contributions across ten sites located in the South Coast Air Basin, California. Eight pollution sources and their contributions were obtained using positive matrix factorization (PMF) from the PM2.5 compositional data collected during the two sampling campaigns (2012/13 and 2018/19) of the Multiple Air Toxics Exposure Study (MATES). The identified sources were "gasoline vehicles", "aged sea salt", "biomass burning", "secondary nitrate", "secondary sulfate", "diesel vehicles", "soil/road dust" and "OP-rich". Among them, "gasoline vehicle" was the largest contributor to the PM2.5 mass. The spatial distributions of source contributions to PM2.5 at the sites were characterized by the Pearson correlation coefficients as well as coefficients of determination and divergence. The highest spatial variability was found for the contributions from the "OP-rich" source in both MATES campaigns suggesting varying influences of the wildfires in the Los Angeles Basin. Alternatively, the smallest spatial variabilities were observed for the contributions of the "secondary sulfate" and "aged sea salt" sources resolved for the MATES campaign in 2012/13. The "soil/road dust" contributions of the sites from the 2018/19 campaign were also highly correlated. Compared to the other sites, the source contribution patterns observed for Inland Valley and Rubidoux were the most diverse from the others likely due to their remote locations from the other sites, the major urban area, and the Pacific Ocean.

Causal association between particulate matter 2.5 and Alzheimer's disease: a Mendelian randomization study

Background

Although epidemiological evidence implies a link between exposure to particulate matter (PM) and Alzheimer's disease (AD), establishing causality remains a complex endeavor. In the present study, we used Mendelian randomization (MR) as a robust analytical approach to explore the potential causal relationship between PM exposure and AD risk. We also explored the potential associations between PM exposure and other neurodegenerative diseases.

Methods

Drawing on extensive genome-wide association studies related to PM exposure, we identified the instrumental variables linked to individual susceptibility to PM. Using summary statistics from five distinct neurodegenerative diseases, we conducted two-sample MR analyses to gauge the causal impact of PM on the risk of developing these diseases. Sensitivity analyses were undertaken to evaluate the robustness of our findings. Additionally, we executed multivariable MR (MVMR) to validate the significant causal associations identified in the two-sample MR analyses, by adjusting for potential confounding risk factors.

Results

Our MR analysis identified a notable association between genetically predicted PM2.5 (PM with a diameter of 2.5 μm or less) exposure and an elevated risk of AD (odds ratio, 2.160; 95% confidence interval, 1.481 to 3.149; p < 0.001). A sensitivity analysis supported the robustness of the observed association, thus alleviating concerns related to pleiotropy. No discernible causal relationship was identified between PM and any other neurodegenerative diseases. MVMR analyses-adjusting for smoking, alcohol use, education, stroke, hearing loss, depression, and hypertension-confirmed a persistent causal relationship between PM2.5 and AD. Sensitivity analyses, including MR-Egger and weighted median analyses, also supported this causal association.

Conclusion

The present MR study provides evidence to support a plausible causal connection between PM2.5 exposure and AD. The results emphasize the importance of contemplating air quality interventions as a public health strategy for reducing AD risk.

Ultra-processed food consumption and metabolic disease risk: an umbrella review of systematic reviews with meta-analyses of observational studies

Background and aims

There is an ongoing debate on whether to advocate reducing ultra-processed food (UPF) in dietary guidelines to control metabolic disease (such as obesity and type 2 diabetes mellitus [T2DM]). We aimed to summarize the evidence from systematic reviews with meta-analyses between UPF consumption and metabolic diseases risk, assess the credibility, and verify the robustness of these associations.

Methods

We systematically searched PubMed, Web of Science, Embase, and Cochrane Library databases from their inception to July 15, 2023, to identify relevant systematic reviews with meta-analyses. We used the random-effects model to evaluate the summary effect size, along with 95% confidence interval and prediction interval. We also assessed heterogeneity, evidence of small-study effects and excess significance bias, and categorized the credibility of each association based on quantitative umbrella review criteria. Additionally, we conducted subgroup and sensitivity analyses to assess the robustness of associations based on continents, study design, dietary assessment methods, definition methods of UPF, population, and units of UPF consumption.

Results

Overall, 6 systematic reviews with 13 meta-analyses were included. Three (23.08%) meta-analyses were classified as highly suggestive evidence for meeting the criteria that associations were significant at p < 10-6, had more than 1,000 cases, and presented the largest study with significance at p < 0.05. Among them, the highest UPF consumption quantile was associated with an increased risk of obesity (OR = 1.55, 95% CI: 1.36-1.77) when compared with the lowest UPF consumption quantile. The highest UPF consumption quantile was associated with an increased risk of T2DM (RR = 1.40, 95% CI: 1.23-1.59) when compared with the lowest UPF consumption quantile, and a 10% increase in UPF consumption (% g/d) was associated with an increased risk of T2DM (RR = 1.12, 95% CI: 1.10-1.13). Meanwhile, the robustness of these associations was verified by a series of subgroup and sensitivity analyses.

Conclusion

UPF consumption may be a risk factor for several metabolic diseases. However, well-designed studies are still needed to verify our findings in the future.

Common and distinct pollution sources identified from ambient PM2.5 concentrations in two sites of Los Angeles Basin from 2005 to 2019

The effects of air quality control policies implemented in California from 2005 to 2019 targeting sources contributing to ambient PM2.5 concentrations, were assessed at two sampling sites in the Los Angeles Basin (N. Main Street and Rubidoux). The spatial and temporal variations of pollution source contributions obtained from dispersion-normalized positive matrix factorization, (DN-PMF) were interpreted with respect to site specific locations. Secondary nitrate and secondary sulfate were the major contributors to the ambient PM2.5 mass concentrations at both sites with substantial concentration decreases after 2008 that were likely due to the implementation of California specific programs including stricter NOx emissions control on motor vehicles. Biomass burning emissions also decreased over the study period at both sampling sites except for one event in December 2005 when strong winter storms and multiple floods led to unusually low atmospheric temperatures and likely increased residential wood burning. The large number of wildfires, trans-Pacific transport of mineral dust and regional dust transported by strong Santa Ana winds and agriculturally generated dust in Rubidoux contributed to poor air quality. Severe storms and devastating wildfires were also linked to the elevated pyrolyzed organic carbon (OP-rich) concentrations. The two distinct region-specific sources, describing fuel combustion in LA, were "residual oil" and "traffic", while separate "gasoline" and "diesel" vehicles sources were identified in Rubidoux. California emissions standards program which required replacement of conventional cars with electric or hybrid vehicles and standards for gasoline and diesel fuels, led to lower "traffic" contributions. Gasoline vehicle emissions after 2017 in Rubidoux also decreased. "Diesel" concentrations declined between 2007 and 2011 because of the recession from late 2007 to early 2009 and the Federal Heavy-Duty Diesel Rule.

The built environment and cardiovascular disease: an umbrella review and meta-meta-analysis

AIMS

To provide a comprehensive overview of the current evidence on objectively measured neighbourhood built environment exposures in relation to cardiovascular disease (CVD) events in adults.

METHODS AND RESULTS

We searched seven databases for systematic reviews on associations between objectively measured long-term built environmental exposures, covering at least one domain (i.e. outdoor air pollution, food environment, physical activity environment like greenspace and walkability, urbanization, light pollution, residential noise, and ambient temperature), and CVD events in adults. Two authors extracted summary data and assessed the risk of bias independently. Robustness of evidence was rated based on statistical heterogeneity, small-study effect, and excess significance bias. Meta-meta-analyses were conducted to combine the meta-analysis results from reviews with comparable exposure and outcome within each domain. From the 3304 initial hits, 51 systematic reviews were included, covering 5 domains and including 179 pooled estimates. There was strong evidence of the associations between increased air pollutants (especially PM2.5 exposure) and increased residential noise with greater risk of CVD. Highly suggestive evidence was found for an association between increased ambient temperature and greater risk of CVD. Systematic reviews on physical activity environment, food environment, light pollution, and urbanization in relation to CVD were scarce or lacking.

CONCLUSION

Air pollutants, increased noise levels, temperature, and greenspace were associated with CVD outcomes. Standardizing design and exposure assessments may foster the synthesis of evidence. Other crucial research gaps concern the lack of prospective study designs and lack of evidence from low-to-middle-income countries (LMICs).

REGISTRATION

PROSPERO: CRD42021246580.

Urban dust particles disrupt mitotic progression by dysregulating Aurora kinase B-related functions

Particulate matter (PM), a major component of outdoor air pollution, damages DNA and increases the risk of cancer. Although the harmful effects of PM at the genomic level are known, the detailed mechanism by which PM affects chromosomal stability remains unclear. In this study, we investigated the novel effects of PM on mitotic progression and identified the underlying mechanisms. Gene set enrichment analysis of lung cancer patients residing in countries with high PM concentrations revealed the downregulation of genes associated with mitosis and mitotic structures. We also showed that exposure of lung cancer cells in vitro to urban dust particles (UDPs) inhibits cell proliferation through a prolonged M phase. The mitotic spindles in UDP-treated cells were hyperstabilized, and the number of centrioles increased. The rate of ingression of the cleavage furrow and actin clearance from the polar cortex was reduced significantly. The defects in mitotic progression were attributed to inactivation of Aurora B at kinetochore during early mitosis, and spindle midzone and midbody during late mitosis. While previous studies demonstrated possible links between PM and mitosis, they did not specifically identify the dysregulation of spatiotemporal dynamics of mitotic proteins and structures (e.g., microtubules, centrosomes, cleavage furrow, and equatorial and polar cortex), which results in the accumulation of chromosomal instability, ultimately contributing to carcinogenicity. The data highlight the novel scientific problem of PM-induced mitotic disruption. Additionally, we introduce a practical visual method for assessing the genotoxic outcomes of airborne pollutants, which has implications for future environmental and public health research.

Health impacts of PM2.5-bound metals and PAHs in a medium-sized Brazilian city

Rio Grande is a medium-sized industrial city located in the extreme south of Brazil, and previous studies in this city have shown contamination by metal(loids) and polycyclic aromatic hydrocarbons (PAHs) in water, soil, and sediment and in the atmosphere. In Brazil, the incorporation of PM_2.5 monitoring in environmental legislation is recent (2018) and, like other developing countries, the number of studies is still small. This study aimed to investigate the levels of PM_2.5 in the industrial and urban area of Rio Grande, to determine the concentration of metal(loid)s As, Cd, Cu, and Pb and of 16 PAHs in the samples of PM_2.5, to perform the health risk assessment for these contaminants and the health impact assessment for two possible scenarios of reduction of PM_2.5 levels. Our main findings regarding the PM_2.5 samples include the following: (1) The levels of this pollutant in the city of Rio Grande were higher than those allowed in current Brazilian legislation, in both the industrial and urban areas; (2) the existence of non-carcinogenic and carcinogenic risks for metals present in all samples; (3) the absence of carcinogenic risk for the assessed PAHs; and (4) the reduction scenarios proposed pointed to a reduction of up to 22 deaths annually in conjunction with reductions in health-related expenditures. Thus, these results may serve as a basis for the development of public health policies aimed at improving air quality, jointly assisting health surveillance and directing future studies towards a better intrinsic approach to the problem.