Ambient carbon monoxide and daily mortality: a global time-series study in 337 cities

Kai Chen, Susanne Breitner, Kathrin Wolf, Massimo Stafoggia, Francesco Sera, Ana M. Vicedo-Cabrera, Yuming Guo, Shilu Tong, Eric Lavigne, Patricia Matus, Nicolás Valdés, Haidong Kan, Jouni J.K. Jaakkola, Niilo R.I. Ryti, Veronika Huber, Matteo Scortichini, Masahiro Hashizume, Yasushi Honda, Baltazar Nunes, Joana MadureiraIulian Horia Holobâcă, Simona Fratianni, Ho Kim, Whanhee Lee, Aurelio Tobias, Carmen Íñiguez, Bertil Forsberg, Christofer Åström, Martina S. Ragettli, Yue Liang Leon Guo, Bing Yu Chen, Shanshan Li, Ai Milojevic, Antonella Zanobetti, Joel Schwartz, Michelle L. Bell, Antonio Gasparrini, Alexandra Schneider

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Background: Epidemiological evidence on short-term association between ambient carbon monoxide (CO) and mortality is inconclusive and limited to single cities, regions, or countries. Generalisation of results from previous studies is hindered by potential publication bias and different modelling approaches. We therefore assessed the association between short-term exposure to ambient CO and daily mortality in a multicity, multicountry setting. Methods: We collected daily data on air pollution, meteorology, and total mortality from 337 cities in 18 countries or regions, covering various periods from 1979 to 2016. All included cities had at least 2 years of both CO and mortality data. We estimated city-specific associations using confounder-adjusted generalised additive models with a quasi-Poisson distribution, and then pooled the estimates, accounting for their statistical uncertainty, using a random-effects multilevel meta-analytical model. We also assessed the overall shape of the exposure–response curve and evaluated the possibility of a threshold below which health is not affected. Findings: Overall, a 1 mg/m3 increase in the average CO concentration of the previous day was associated with a 0·91% (95% CI 0·32–1·50) increase in daily total mortality. The pooled exposure–response curve showed a continuously elevated mortality risk with increasing CO concentrations, suggesting no threshold. The exposure–response curve was steeper at daily CO levels lower than 1 mg/m3, indicating greater risk of mortality per increment in CO exposure, and persisted at daily concentrations as low as 0·6 mg/m3 or less. The association remained similar after adjustment for ozone but was attenuated after adjustment for particulate matter or sulphur dioxide, or even reduced to null after adjustment for nitrogen dioxide. Interpretation: This international study is by far the largest epidemiological investigation on short-term CO-related mortality. We found significant associations between ambient CO and daily mortality, even at levels well below current air quality guidelines. Further studies are warranted to disentangle its independent effect from other traffic-related pollutants. Funding: EU Horizon 2020, UK Medical Research Council, and Natural Environment Research Council.

Original languageEnglish
Pages (from-to)e191-e199
Number of pages9
JournalThe Lancet Planetary Health
Issue number4
Publication statusPublished - 1 Apr 2021

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