Short-term exposures to PM2.5 and cause-specific mortality of cardiovascular health in China
Introduction
Short-term exposure to fine particle [Particulate Matter < 2.5 µm in aerodynamic diameter (PM2.5)] pollution has been linked to adverse cardiovascular effects (Englert, 2004, Pope and Dockery, 2006, Brook et al., 2004). Over the last decade, efforts to understand and mitigate the effects of PM2.5 concentrations at below-guideline levels on human health and welfare have been made through a great deal of multi-center epidemiologic research in the United States, Europe, and other developed countries (Ostro et al., 2006, Franklin et al., 2007, Zanobetti and Schwartz, 2009). The results of these studies have been well applied to improve the mitigation of local air pollution and the development of methods designed to protect the health of local populations. However, few related studies have been conducted in developing countries due to limitations of available data, funding and other reasons. In many cases, the PM2.5 pollution levels in these countries are much higher than the levels in the developed world (Van Donkelaar et al., 2015), and this is coupled with quite distinct characteristics of the population and the socio-economic status of those societies. As a result, evidence of developed countries cannot be readily applied to the air pollution policy-making and related public health protection efforts of developing countries. Moreover, another critical gap in our current knowledge is whether specific individuals or population subgroups experience a greater level of risk due to short-term exposure to PM2.5 (Pope and Dockery, 2006, Clougherty, 2010). For the reasons above, it is critical for researchers to conduct epidemiologic work on air pollution in developing countries to fill these missing gaps of knowledge.
The rapid industrialization of China, one of the largest developing countries, in the past few decades has significantly increased China's air pollution levels (Kan et al., 2012, Shang et al., 2013, Gao et al., 2011). The cities of Beijing, Shijiazhuang, Chengdu, and Xi’an have recently reported annual levels of PM2.5 at around 87, 144, 89, and 97 μg/m3, respectively, during 2013–2014 (Wang et al., 2014). At the same time, the Chinese population is currently experiencing a heavy burden from cardiovascular disease; in 2005, cardiovascular disease accounted for 32% of all deaths and 13% of total disability-adjusted life-years lost in China (Wang et al., 2005). In addition, with China's aging population growing, these numbers continue to increase (Ezzati et al., 2015, Moran et al., 2010). Atkinson et al. (2014) summarized the existing epidemiologic evidence related to PM2.5 and cardiovascular mortality in the literature up to 2011 and presented estimates for various WHO regions. However, Western Pacific Area-A, which is mainly made up of China, was not included in this meta-analysis because no available studies met the eligibility criteria. Although some single-center time-series studies provided partial insight (Huang et al., 2012, Yang et al., 2012, Li et al., 2013, Chen et al., 2013), those studies had concentrated on several large cities and focused on the endpoints of all-cause death rather than addressing cardiovascular or other specific causes of death. In addition, to date, relatively few multi-center studies have been conducted in China (Shang et al., 2013, Lu et al., 2015). Compared with single-center studies, multi-center studies has several distinct advantages, especially in terms of strengthening the power of the statistical analysis and reducing the likelihood of spurious results (Anderson et al., 2005, Pope and Dockery, 2006).
Given the severe pollution situation and the knowledge gaps mentioned above, it is worth initiating more in-depth and larger epidemiological studies to understand of the acute health effects of PM2.5 on cardiovascular death in China. Generating a complete PM2.5-mortality exposure response relationship and determining the effect size of PM2.5 on cause-specific cardiovascular death is also essential. Knowledge related to the subpopulations that are sensitive to PM2.5 will be necessary for guiding future strategies designed to protect the population from the adverse effects of air pollution. Thus, in this paper, we conducted a multi-county time series analysis to investigate the short-term effects of PM2.5 on cause-specific mortality of cardiovascular health across China, and to explore which groups are at a relatively higher risk or are more susceptible to the adverse effects of PM2.5 exposure.
Section snippets
Study site
Thirty Chinese counties with a total resident population of 23.7 million were selected for our study. These counties were located in the major cities of northern, eastern and southwestern China (Fig. 1) and includes 21 urban and 9 rural areas. Counties of interest were selected based on the availability of daily mortality data, PM2.5 and O3 concentration data, and meteorological factors with a baseline of at least 900 days from January 1, 2013 to December 31, 2015.
Mortality data
Daily mortality counts were
Results
Among the populations of the 30 counties analyzed during the study period of 2013–2015, 379,133 deaths occurred from natural causes, of which 164,061 were related to CVD, 69,041 to CHD, 26,098 to AMI, and 49,669 to stroke. Fig. 1 shows the locations of the mortality within the 30 counties with their corresponding levels of PM2.5 concentration at the city scale during 2013–2015. In general, most people in these counties were exposed to a mean concentration of PM2.5 above 50 μg/m3 (ranging from
Discussion
In this time series study of people in 30 Chinese counties covering nearly 380,000 deaths between 2013 and 2015, short-term exposures to PM2.5 were associated with increased daily mortality risk from natural causes, CVD and AMI. The associations were found at a daily average PM2.5 concentration near 72 μg/m3. Our analysis also provided evidence that people 65–74 years old might be more vulnerable to PM2.5 exposure. In addition, significant effects of PM2.5 on mortality of cardiovascular causes
Conclusion
Our multi-center time series study focused on obtaining the temporal relationship of short-term exposure to PM2.5 and cause-specific mortality related to the human cardiovascular health as well as identifying sensitive subpopulations in China. The magnitude of PM2.5 acute effect on cardiovascular mortality was lower than those reported in Europe and America. These findings shed new light on the differences between the acute health effects of PM2.5 on the people mortality of cardiovascular
Acknowledgements
This research was funded by grants from National Natural Science Foundation of China (Grant: 21277135, 91543111), Beijing Municipal Natural Science Foundation (7172145), National High-Level Talents Special Support Plan of China for Young Talents National Institute of Environmental Health.
A competing financial interests declaration
The authors declare they have no actual or potential competing financial interests.
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