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Research Article
October 18, 2023
Letter to the Editor

Short-term Exposure to Air Pollution and Ischemic Stroke
A Systematic Review and Meta-analysis

November 7, 2023 issue
101 (19) e1922-e1932

Abstract

Background and Objectives

Approximately 5 million fatalities occur annually due to stroke, along with its substantial effects on patient well-being and functional impairment. Research has established a connection between extended exposure to air pollutants and ischemic stroke. However, the link between short-term exposure to air pollutants and stroke remains less definitive.

Methods

A comprehensive search was conducted on MEDLINE, Scopus, the Cochrane Central Register of Controlled Trials (CENTRAL), and Web of Sciences databases up until February 2023, without any language restrictions. The inclusion criteria encompassed observational or interventional studies that examined the correlation between short-term exposure to air pollutants (carbon monoxide [CO], sulfur dioxide [SO2], nitrogen dioxide [NO2], ozone [O3]) and particulate matter with diameters of less than 1 µm, less than 2.5 µm, or less than 10 µm (PM1, PM2.5, and PM10), with the incidence and mortality of ischemic stroke. Short-term exposure was defined as exposure occurring within 5 days of the onset of stroke.

Results

A total of 18,035,408 cases of ischemic stroke were included in the analysis, derived from 110 observational studies. Asia accounted for most included studies, representing 58.8% of the total. By contrast, Europe and the Americas contributed 24.6% and 16.7% of the studies, respectively. Notably, none of the included studies were conducted in Africa. Stroke incidence was significantly associated with an increase in the concentration of NO2 (RR = 1.28; 95% CI 1.21–1.36), O3 (RR = 1.05; 95% CI 1.03–1.07), CO (RR = 1.26; 95% CI 1.21–1.32), SO2 (RR = 1.15; 95% CI 1.11–1.19), PM1 (RR = 1.09; 95% CI 1.06–1.12), PM2.5 (RR = 1.15; 95% CI 1.13–1.17), and PM10 (RR = 1.14; 95% CI 1.12–1.16). Moreover, an increase in the concentration of NO2 (RR = 1.33; 95% CI 1.07–1.65), SO2 (RR = 1.60; 95% CI 1.05–2.44), PM2.5 (RR = 1.09; 95% CI 1.04–1.15), and PM10 (RR = 1.02; 95% CI 1.00–1.04) was associated with an increase in stroke mortality.

Discussion

There is a strong and significant correlation between gaseous and particulate air pollutants and the occurrence and mortality rates of stroke. This close temporal association underscores the importance of implementing global initiatives to develop policies aimed at reducing air pollution. By doing so, alleviate the burden of ischemic stroke and its consequences.

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Supplementary Material

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Letters to the Editor
13 March 2024
Reader Response: Short-term Exposure to Air Pollution and Ischemic Stroke: A Systematic Review and Meta-analysis
Lauren Grobois | School of Medicine | New York Medical College
Michelle You | School of Medicine | New York Medical College
Mill Etienne | School of Medicine | New York Medical College

We read the recent article “Short-term Exposure to Air Pollution and Ischemic Stroke: A Systematic Review and Meta-analysis” by Toubasi and Al-Sayegh with great interest. In their study, the authors hypothesize that air pollution exposure is correlated with increased ischemic stroke risk globally, and they highlight the far-reaching impact of environmental injustice.1 They show that even short-term exposure to air pollutants was associated with stroke and stroke mortality. This conclusion supports hypothesized notions of air pollution’s association with neurologic disease risk.

As our climate continues to change and we face more frequent and intense ramifications of pollution, doctors around the world need to consider the neurologic consequences. Recent US Census data shows that inhabitants of densely populated cities are increasingly young, non-White, Hispanic, and of low socioeconomic status.2 These groups are exposed to a greater degree of pollution than their peers living in less-populated areas.3  

Many studies have explored the connection between race, ethnicity, and socioeconomic status and increased stroke risk.4 However, recent data also highlights increased stroke incidence in people under 50 years of age.5 This raises the question: is pollution a factor in this shift? More research must be done to explore this correlation. Environmental changes affect everyone, but we must address the needs of vulnerable communities to lessen the continued divide among people from different backgrounds, both locally and globally.

References

  1. Toubasi A, Al-Sayegh TN. Short-term Exposure to Air Pollution and Ischemic Stroke: A Systematic Review and Meta-analysis. Neurology. 2023;101(19):e1922-e32.doi: 10.1212/WNL.0000000000207856.
  2. Exploring Age Groups in the 2020 Census. US Census Bureau. Updated May 25, 2023. Accessed February 9, 2024. https://www.census.gov/library/visualizations/interactive/exploring-age-groups-in-the-2020-census.html
  3. Krzyzanowski M, Apte JS, Bonjour SP, Brauer M, Cohen AJ, Prüss-Ustun AM. Air pollution in the mega-cities. Current Environmental Health Reports1. 2014;185-191.
  4. Tsao CW, Aday AW, Almarzooq ZI, et al. Heart Disease and Stroke Statistics—2023 Update: A Report From the American Heart Association. 2023;147:e93–e621.
  5. Krishnamurthi RV, Moran AE, Feigin VL, et al., and the GBD 2013 Stroke Panel Experts Group. Stroke Prevalence, Mortality and Disability-Adjusted Life Years in Adults Aged 20-64 Years in 1990-2013: Data from the Global Burden of Disease 2013 Study. Neuroepidemiology. 2015;45(3):190–202.

Author disclosures are available upon request ([email protected]).

1 February 2024
Author Response: Short-term Exposure to Air Pollution and Ischemic Stroke: A Systematic Review and Meta-analysis
Ahmad A. Toubasi | Faculty of Medicine, the University of Jordan, Amman, Jordan

We thank Lin and Zhou for their interest in our article.1 The definition of 'short-term exposure' to air pollution within 7 days before ischemic stroke is a period that has already been validated.2,3 The studies varied regarding single or multiple pollutants in their models. This variability might have contributed to the significant heterogeneity in the models. However, it is important to note that including estimates from single or multiple air pollutants might not significantly impact the results. Several previous studies indicated that the increase in one pollutant is usually accompanied by an increase in other pollutants. 4,5 In addition, air pollutants are correlated with several meteorological factors such as wind and temperature.4,5 The interpretation of our results should not be based on single pollutants but rather based on the impact of all the pollutants as most of these chemicals are emitted from the same sources.       

We acknowledge that our models had high heterogeneity attributed to systemic differences in the baseline characteristics of the underlying population and measurement of the exposure and outcome. We used random effect analysis in our models to account for this heterogeneity which is a well-known method to deal with heterogenous models.6 This method weighs the studies inversely by the total study variations including between-study variations 6

In addition, we accounted for this heterogeneity by conducting subgroup analysis according to the quality of the study scored using the Newcastle Ottawa Scale. We did not use meta-regression in the analysis due to its limitations when used with heterogenous models including low power and the requirement of notable variation of its independent variable 7.

  1. Toubasi A, Al-Sayegh TN. Short-term Exposure to Air Pollution and Ischemic Stroke. Neurology. 2023;101(19):e1922-e1932. doi:doi:10.1212/WNL.0000000000207856
  2. Matsuo R, Michikawa T, Ueda K, et al. Short-Term Exposure to Fine Particulate Matter and Risk of Ischemic Stroke. Stroke. 2016;47(12):3032-3034. doi:doi:10.1161/STROKEAHA.116.015303
  3. Xu R, Wang Q, Wei J, et al. Association of short-term exposure to ambient air pollution with mortality from ischemic and hemorrhagic stroke. Eur J Neurol.2022;29(7):1994-2005. doi:https://doi.org/10.1111/ene.15343
  4. Jiang Y, Chen J, Wu C, et al. Temporal cross-correlations between air pollutants and outpatient visits for respiratory and circulatory system diseases in Fuzhou, China. BMC Public Health. 2020;20(1):1131. doi:10.1186/s12889-020-08915-y
  5. Liu Y, Zhou Y, Lu J. Exploring the relationship between air pollution and meteorological conditions in China under environmental governance. Scientific Reports. 2020;10(1):14518. doi:10.1038/s41598-020-71338-7
  6. Imrey PB. Limitations of Meta-analyses of Studies With High Heterogeneity. JAMA Network Open. 2020;3(1):e1919325-e1919325. doi:10.1001/jamanetworkopen.2019.19325 %J JAMA Network Open
  7. Stanley TD, Doucouliagos H, Ioannidis JPA. Beyond Random Effects: When Small-Study Findings Are More Heterogeneous. 2022;5(4):25152459221120427. doi:10.1177/25152459221120427

Author disclosures are available upon request([email protected]).

31 January 2024
Reader Response: Short-term Exposure to Air Pollution and Ischemic Stroke A Systematic Review and Meta-analysis
Wenjian Lin | Shanghai Tenth People's Hospital, Tongji University School of Medicine, Shanghai, China
Xiaoyu Zhou | Shanghai Tenth People's Hospital, Tongji University School of Medicine, Shanghai, China

We read the article by Toubasi and Al-Sayegh1 with great interest and concur with the premise that short-term exposure to air pollution is associated with an increased risk of stroke.1,2 We would, however, like to point out an inconsistency within the article regarding the definition of 'short-term exposure' to air pollution. In the 'Methods' section of the abstract, this term is defined as a period of 5 days, while in the 'Search Strategy' section, it is referred to as 7 days.

Several high-quality studies have uniformly defined short-term exposure as a period of up to 7 days.2,3 Additionally, we believe that it would enhance the clarity of such studies if they explicitly stated whether a single or multiple air-pollutant model was utilized in their methodology. Upon reviewing Toubasi and Al-Sayegh’s research, we observed a considerable degree of heterogeneity in most outcomes. This observation leads us to suggest that the exclusive use of the Castle-Ottawa scale for subgroup analysis may not be sufficient in these cases. Instead, we propose the incorporation of meta-regression analysis for a more thorough examination, to be used in tandem with the Newcastle-Ottawa scale for subgroup analysis.5

  1. Toubasi A, Al-Sayegh TN. Short-term Exposure to Air Pollution and Ischemic Stroke: A Systematic Review and Meta-analysis. Neurology. 2023;101(19):e1922-e32.doi: 10.1212/WNL.0000000000207856.
  2. Lin W, Pan J, Li J, et al. Short-term Exposure to Air Pollution and the Incidence and Mortality of Stroke: A Meta-Analysis. Neurologist. 2023;24(11):1-7.doi: 10.1097/NRL.0000000000000544.
  3. Shah ASV, Lee KK, McAllister DA, et al. Short term exposure to air pollution and stroke: systematic review and meta-analysis. BMJ. 2015;350:h1295.doi: 10.1136/bmj.h1295.
  4. Shah AS, Langrish JP, Nair H, et al. Global association of air pollution and heart failure: a systematic review and meta-analysis. Lancet. 2013;382(9897):1039-1048.
  5. Shamseer L, Moher D, Clarke M, et al.; PRISMA-P Group. Preferred reporting items for systematic review and meta-analysis protocols (PRISMA-P) 2015: elaboration and explanation. BMJ. 2015;350:g7647. doi: 10.1136/bmj.g7647. 

Author disclosures are available upon request([email protected]).

Information & Authors

Information

Published In

Neurology®
Volume 101Number 19November 7, 2023
Pages: e1922-e1932
PubMed: 37758483

Publication History

Received: May 22, 2023
Accepted: July 28, 2023
Published online: September 27, 2023
Published in print: November 7, 2023

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Disclosure

The authors report no relevant disclosures. Go to Neurology.org/N for full disclosures.

Study Funding

The authors report no targeted funding.

Authors

Affiliations & Disclosures

From the Faculty of Medicine, the University of Jordan, Amman.
Disclosure
Scientific Advisory Boards:
1.
NONE
Gifts:
1.
NONE
Funding for Travel or Speaker Honoraria:
1.
NONE
Editorial Boards:
1.
NONE
Patents:
1.
NONE
Publishing Royalties:
1.
NONE
Employment, Commercial Entity:
1.
NONE
Consultancies:
1.
NONE
Speakers' Bureaus:
1.
NONE
Other Activities:
1.
NONE
Clinical Procedures or Imaging Studies:
1.
NONE
Research Support, Commercial Entities:
1.
NONE
Research Support, Government Entities:
1.
NONE
Research Support, Academic Entities:
1.
NONE
Research Support, Foundations and Societies:
1.
NONE
Stock/stock Options/board of Directors Compensation:
1.
NONE
License Fee Payments, Technology or Inventions:
1.
NONE
Royalty Payments, Technology or Inventions:
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Legal Proceedings:
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Thuraya N. Al-Sayegh, MD
From the Faculty of Medicine, the University of Jordan, Amman.
Disclosure
Scientific Advisory Boards:
1.
NONE
Gifts:
1.
NONE
Funding for Travel or Speaker Honoraria:
1.
NONE
Editorial Boards:
1.
NONE
Patents:
1.
NONE
Publishing Royalties:
1.
NONE
Employment, Commercial Entity:
1.
NONE
Consultancies:
1.
NONE
Speakers' Bureaus:
1.
NONE
Other Activities:
1.
NONE
Clinical Procedures or Imaging Studies:
1.
NONE
Research Support, Commercial Entities:
1.
NONE
Research Support, Government Entities:
1.
NONE
Research Support, Academic Entities:
1.
NONE
Research Support, Foundations and Societies:
1.
NONE
Stock/stock Options/board of Directors Compensation:
1.
NONE
License Fee Payments, Technology or Inventions:
1.
NONE
Royalty Payments, Technology or Inventions:
1.
NONE
Stock/stock Options, Research Sponsor:
1.
NONE
Stock/stock Options, Medical Equipment & Materials:
1.
NONE
Legal Proceedings:
1.
NONE

Notes

Correspondence Dr. Toubasi [email protected]
Go to Neurology.org/N for full disclosures. Funding information and disclosures deemed relevant by the authors, if any, are provided at the end of the article.
Submitted and externally peer reviewed. The handling editor was Editor-in-Chief José Merino, MD, MPhil, FAAN.

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Cited By
  1. Influence of Air Pollution Exposures on Cardiometabolic Risk Factors: a Review, Current Environmental Health Reports, (2023).https://doi.org/10.1007/s40572-023-00423-6
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