Is smaller worse? New insights about associations of PM1 and respiratory health in children and adolescents
Introduction
Several recent reviews on associations between ambient air pollution and respiratory health such as asthma and allergic rhinitis showed controversial conclusions (Anderson et al., 2013; Bowatte et al., 2015; Fuertes and Heinrich, 2015; Gowers et al., 2012; Guarnieri and Balmes, 2014; Heinrich et al., 2016; Khreis et al., 2017; Jacquemin et al., 2015). Reviews that included both cross-sectional and longitudinal studies supported a positive association between air pollution and respiratory health (Khreis et al., 2017), while those based exclusively on longitudinal studies did not show these associations (Bowatte et al., 2015; Fuertes and Heinrich, 2015; Heinrich et al., 2016; Jacquemin et al., 2015). One hypothesis attributes these differences, at least partially, to regional differences in air pollution composition and concentrations (Burbank and Peden, 2018; Cheng et al., 2016; Guarnieri and Balmes, 2014; Jiřík et al., 2017; Liu et al., 2017; Rice et al., 2018; Watanabe et al., 2017). Since most existing studies are from European and North American areas with comparatively low exposures, there is a need to study associations between air pollution and respiratory health in high exposure settings, such as in Asia (Doğruel et al., 2017; Gerez et al., 2010; Kou et al., 2018; Pinart et al., 2017). In China, high rates of population growth, coupled with rapid industrial development and urbanization, have led to well-publicized air quality concerns due to the coexistence of intense coal smoke and motor vehicle emissions. Therefore, China presents an ideal opportunity to examine the effects of ambient air pollution on respiratory health.
While the effects of airborne particulate matter (PM) with aerodynamic diameters <2.5 μm (PM2.5) on asthma and allergies have been widely investigated (Bose et al., 2018; Khalili et al., 2018; Keet et al., 2018; Lavigne et al., 2018; Pennington et al., 2018), few studies have characterized respiratory health impacts for the smaller, and potentially more toxic PM size fraction <1 μm aerodynamic diameter (PM1). PM2.5 can penetrate the small airways and alveoli of the lower respiratory tract, leading to potentially more pronounced health effects (Chen et al., 2017; Mei et al., 2018). PM1 particles are even smaller, and are characterized by high surface area to volume ratio, having an even greater potential for deleterious biological interactions with respiratory tissues and risks for adverse health outcomes (Mei et al., 2018; Borm et al., 2006; Seaton et al., 2010). However, PM1 is not routinely measured because it is not subject to air quality standards in most countries and limited data are available to characterize exposure (Chen et al., 2017; Krzyzanowski, 2008).
In a systematic Medline search, we identified only six relevant human studies examining the effect of PM1 exposure on human health (Chen et al., 2017; Hassanvand et al., 2017; Lin et al., 2016; Wang et al., 2018; Chen et al., 2015; Yang et al., 2018a, Yang et al., 2018b), but none of these studies looked at respiratory outcomes. Furthermore, among these six human-related studies, two studies were panel studies (Chen et al., 2015; Hassanvand et al., 2017), and three studies were both based on Chinese disease monitoring data (Chen et al., 2017; Wang et al., 2018). Only our 33 Communities Chinese Health Study (33CCHS) previously provided a large general population investigation to evaluate the associations of PM1 with diabetes and metabolic syndrome (Yang et al., 2018a, Yang et al., 2018b). To begin to address the absence of evidence on ambient PM1 and children's respiratory health, we used data from the Seven Northeastern Cities (SNEC) Study. Our primary aim was to evaluate the effects of PM2.5 and PM1 on asthma, asthma-related symptoms, and allergic rhinitis in children aged 2 to 17 years. As a secondary aim, we explored whether these associations were modified by sex and allergic predisposition.
Section snippets
Study population and participants
The SNEC was a large population based study designed to examine health outcomes in association with ambient PM exposure among children residing in Liaoning Province, a highly industrialized area in northeastern China. To maximize the contrasts of ambient PM concentrations, in April 2012, we selected 27 urban districts in seven cities as study sites, based on mean air pollution levels during 2009–2012. In total, we selected six districts in Shenyang, five districts in Dalian, four districts in
Characteristics of the study population
From the 63,910 participants, we excluded 4156 children and adolescents (6.50%) that had resided in their current residential address for <2 years. In the final sample of 59,754 children and adolescents, the average age was 10.31 years, and 50.64% were boys. As shown in Table 1, the overall prevalence of doctor-diagnosed asthma (9.51% vs. 6.07%), current asthma (3.50% vs. 1.98%), current wheeze (4.61% vs. 3.31%), wheeze (12.79% vs. 10.07%), persistent phlegm (3.43% vs. 2.80%), persistent cough
Discussion
In this large population-based study in northeastern China, we detected associations between higher concentrations of ambient PM1 and PM2.5 and greater odds for clinical asthma diagnosis and self-reported asthma-like symptoms. All the associations were more pronounced in boys than girls and in those with allergic predisposition than in their non-allergy predisposed counterparts.
Acknowledgement
This work was supported by Major Program of National Natural Science Foundation of China (91543208), Science and Technology Program of Guangzhou (201807010032), the National Natural Science Foundation of China (81872582, 81673128, 81703179, 81472936), National Key Research and Development Program of China (2016YFC0207000), Fundamental Research Funds for the Central Universities (16ykzd02, 17ykpy14, 17ykpy16), Science and Technology Planning Project of Guangdong Province (2014A050503027,
Competing financial interests
The authors declare they have no actual or potential competing interests.
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These authors contributed equally to this work and should both be list as the first author.