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 María Vicedo-Cabrera, Yuming Guo, Shilu Tong, Éric Lavigne, Patricia Matus, Nicolás Valdés, Haidong Kan, Jouni J. K. Jaakkola, Niilo Ryti, Veronika Huber, Matteo Scortichini, Masahiro Hashizume, Yasushi Honda, Baltazar Nunes, Joana Madureira, Iulian‐Horia Holobâcă, Simona Fratianni, Ho Kim, Whanhee Lee, Aurelio Tobı́as, Carmen Íñiguez, Bertil Forsberg, Christofer Åström, Martina S. Ragettli, Yue Leon Guo, Bing-yu Chen, Shanshan Li, Ai Milojevic, Antonella Zanobetti, Joel Schwartz, Michelle L. Bell, Antonio Gasparrini, Alexandra Schneider
Abstract
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: 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.