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Multi-Country Analysis Confirms Increased Mortality Risk from Air Pollution

MedicalResearch.com Interview with:
Cong Liu, PhD

Department of Environmental Health
School of Public Health
Fudan University
Shanghai 200032, China

MedicalResearch.com: What is the background for this study?

Response: Numerous time-series studies have examined the short-term associations between particulate air pollution (PM10 and PM2.5) exposures and daily mortality. However, most evidence has been obtained from studies in single cities, regions, or countries. There are challenges in comparing these results and in synthesizing effect estimates because of different modeling approaches and potential publication bias. Furthermore, there has never been a global representative concentration-response function for risk assessment and policy making.

We and our co-authors established the Multi-City Multi-Country (MCC) Collaborative Research Network to perform a global assessment of the effects of weather or climate on mortality. This network allowed us to examine and compare the associations of PM concentrations with daily mortality at the global, regional, and country level with the use of a standardized analytic framework.

MedicalResearch.com: What are the main findings?

  • The largest study so far on the independent associations between short-term exposure to particulate matter (PM10 and PM5) and mortality, analysing data from 652 cities in 24 countries/regions
  • First study to apply consistent analytical methods to compare estimates across countries and regions, including developing areas
  • The pooled results indicate an increased risk in all-cause mortality risk of 0.44% and 0.68% per a 10-μg/m3 increase of PM10 and PM5, respectively
  • The estimated association was approximately linear without discernible threshold even at exposure levels below the current air-quality guidelines and regulatory limits, but with steeper slopes at lower PM concentrations 

MedicalResearch.com: What should readers take away from your report?

  • Evidence on an independent effect of short-term particulate matter exposure in increasing the risk of all-cause and cause-specific mortality, consistently across 652 cities in 24 countries/regions.
  • Differences across countries and regions are attributable to different ranges of PM exposures, with higher effects at lower ranges.
  • The concentration-response curve indicates no discernible threshold, with significant increases in mortality even at exposure levels below the current Air Quality Guidelines, suggesting a need to tighten these regulatory limits.

MedicalResearch.com: What recommendations do you have for future research as a result of this work? 

  • Using a unified analytical protocol, this study synthesized a short-term association between PM and mortality at a global level. The same idea may be applicable to pool the results from long-term studies, such as cross-sectional designs or cohort studies with prospective designs.
  • The exposure assessment of this study relies on fixed-site monitoring, which may introduce measurement error. With the rapid development in modeling framework, such as satellite retrievals, chemical transport models, and machine learning techniques, a more precise and feasible exposure assessment may be warranted in future analysis.
  • Identifying the specific constituents of particulate matter that are mainly responsible for mortality risk and other health outcomes. 

Disclosures: The corresponding author Haidong Kan, was supported by the National Natural Science Foundation of China (91843302 and 91643205), and China Medical Board Collaborating Program (Grant 16-250). The senior author Antonio Gasparrini, was supported by the Medical Research Council UK (MR/R013349/1 and MR/M022625/1)


Ambient Particulate Air Pollution and Daily Mortality in 652 Cities

Cong Liu, M.S., Renjie Chen, Ph.D., Francesco Sera, Ph.D., Ana M. Vicedo-Cabrera, Ph.D., Yuming Guo, Ph.D., Shilu Tong, Ph.D., Micheline S.Z.S. Coelho, Ph.D., Paulo H.N. Saldiva, Ph.D., Eric Lavigne, Ph.D., Patricia Matus, Ph.D., Nicolas Valdes Ortega, M.Sc., Samuel Osorio Garcia, Ph.D.

August 22, 2019
N Engl J Med 2019; 381:705-715
DOI: 10.1056/NEJMoa1817364


Last Modified: [last-modified]


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Last Updated on August 22, 2019 by Marie Benz MD FAAD