Air pollution and cardiovascular heath in a changing climate

Abstract

Air pollution is one of the major causes of mortality and morbidity in the world today. World Health Organization (WHO) data show that almost all of the global population (99%) breathe air that exceeds WHO guideline limits and contains high levels of pollutants, with low- and middle-income countries suffering most from air pollution exposure. In China, the largest developing country, the poor air quality is primarily attributed to the rapid economic expansion the country experienced since the reform and opening-up in 1978, resulting in a drastic increase in coal-powered industrial production and electricity demand, as well as an exponential rise in private vehicles. Although there has been continuous air quality improvement following a series of stringent control policies, air pollution remains an important public health threat in China. The Global Burden of Disease Study estimated that in 2019, air pollution was responsible for 1.85 million deaths in China[1]. Meanwhile, non-communicable diseases (NCDs), such as cardiovascular disease and cancer, have placed much more disease burden on the population than ever[2]. It has been estimated that cardiovascular disease is now the leading cause of death in the Chinese population of adults 40 years of age and older, accounting for around 40% of total mortality. A growing body of human and animal evidence has led to a concern about the potential deleterious effects of ambient air pollution on the cardiovascular system[3,4]. For example, using the largest nationwide data in 272 Chinese cities, Chen et al. reported that a 10 μg/m3 increment of PM2.5 was associated with an increase of 0.27% in cardiovascular mortality. Similarly, in 652 cities of 24 countries, Liu et al. reported that an increase of 10 μg/m3 increment of PM2.5 was associated with increases of 0.36% in daily cardiovascular mortality[5]. The mixture of air pollutants may adversely affect the cardiovascular system directly and indirectly[6]. Direct effects may occur via agents that readily cross the pulmonary epithelium into the circulation, such as ultra-fine particles (UFPs), soluble constituents of particles (e.g., sulfate and nitrate), and gaseous pollutants (e.g., nitrogen oxides). Indirect effects may occur via induction of pulmonary inflammation and oxidative stress, leading to systemic inflammation and endothelial dysfunction. Although the adverse cardiovascular effects of air pollution have been documented in China, questions remain to be solved in human-based studies, especially for a stronger causal inference[7]. In this issue, we invited esteemed colleagues from some of the most reputable institutions in China and the United States, including Yale University, the Chinese Center for Disease Control and Prevention, Fudan University, and Chinese Academy of Medical Sciences and Peking Union Medical College to report their latest findings on air pollution and cardiovascular disorders. Their intriguing findings underscore the importance of understanding the health impacts of air pollution, particularly in China where the problem is especially severe due to rapid industrialization and urbanization. Ban et al. investigated the linear and non-linear patterns for the association between PM2.5 and acute incidence of myocardial infarction (MI) based on a multi-county registry dataset. They evaluated the reduction of premature MI incidence under different pollution control objectives in China[8]. This study provided valuable insights into the impact of PM2.5 on cardiovascular health on a national scale, and its findings can help inform policies aimed at reducing the burden of cardiovascular disease in China. Du et al. investigated the health effects of short-term exposure to PM2.5 from agricultural sources on acute MI onset using a nationwide database in China[9]. The study found that exposure to agricultural PM2.5 was associated with an increased risk of acute MI, highlighting the need for more research on estimating the adverse health effects of different air pollution sources. The study conducted by Jiang et al. explored the impacts of PM2.5 and PM2.5–10 on the onset of stable and unstable angina at an hourly temporal resolution, adjusting for key confounders[10]. They suggest that life-threatening cardiovascular disease risk from transient exposure to air pollution must be considered by healthcare professionals including cardiologists and patient caregivers to avoid negative cardiorespiratory outcomes. Finally, Zhou et al. reviewed available evidence quantifying the relationship between exposure to ambient gaseous and particulate air pollutants and cardiovascular symptoms[11]. The study found that exposure to air pollution was associated with a wide range of cardiovascular symptoms, including heart failure, arrhythmias, and hypertension. Although the findings above confirm that air pollution contributes to the cardiovascular disorders in China, several questions or challenges remain to be solved in human-based studies, especially for a stronger causal inference. Although some recent prospective cohort studies in China have examined the long-term effects of air pollution on cardiovascular mortality or morbidity[12], cohort studies are still lacking in examining a full spectrum of cardiometabolic diseases. Most Chinese studies on air pollution and cardiovascular health are observational in nature, thus limiting the power of causal inference. Accountability studies that evaluate long-term health benefits of clean air policies and intervention studies that reduce individual exposure may help to establish a causal relationship between air pollution and cardiovascular health[13]. The application of the difference-in-differences approach and randomized crossover design in intervention studies have been shown to further improve the causality[14]. Controlled-exposure human trials are particularly useful to establish the biological causation for the adverse cardiovascular effects of air pollution[15]. As research on the relationship between air pollution and cardiovascular health in the Chinese population continues to evolve, it is important to remember the many questions and challenges that remain. One area requiring further investigation is the lifetime course of cardiovascular damage effects, which could be addressed through prospective cohort studies. By following a large cohort of individuals over time, researchers can better understand how air pollution exposure affects the development and progression of cardiovascular diseases over the course of an individual’s life. In addition to clarifying the long-term effects of air pollution on cardiovascular health, it is also important to examine the relevance of cumulative exposure. This requires not only tracking the levels of air pollution that individuals are exposed to over time but also considering how exposure to other risk factors, such as smoking, physical activities, green space, or a poor diet, may interact with air pollution exposure to affect cardiovascular health outcomes. By taking a more comprehensive approach to understanding the health impacts of air pollution, researchers can help to identify the most vulnerable populations and periods and develop more effective public health interventions to mitigate the negative health effects of air pollution. Another crucial area for future research is the investigation of genetic–environment interactions in relation to air pollution exposure and cardiovascular health. While genetic factors have been shown to play a role in the development of cardiovascular disease, their interaction with environmental factors such as air pollution is still poorly understood. By identifying genetic variations that may increase an individual’s susceptibility to the negative health effects of air pollution, researchers can help to develop more personalized approaches to the prevention and treatment of cardiovascular diseases. Finally, it is important to establish the pathophysiologic link between air pollution and cardiometabolic diseases in the Chinese population. This requires identifying the specific mechanisms by which air pollution exposure leads to cardiovascular disease and understanding how these mechanisms may differ across different population subgroups. By gaining a more detailed understanding of the biological pathways that link air pollution exposure to cardiovascular disease, researchers can help to develop more targeted and effective interventions to mitigate the negative health effects of air pollution. Beyond these research priorities, there is clear evidence showing that climate change poses significant health risks to the population, and population health risks due to environmental factors under changing climate will become more severe in the future[16]. Air quality is closely linked to the earth’s climate and ecosystems globally, as many of the air pollutants and greenhouse gases share the same sources (e.g., combustion of fossil fuels). Therefore, policies to reduce air pollution offer a win-win strategy for both climate and health, lowering the burden of disease attributable to air pollution, and contributing to the near- and long-term mitigation of climate change can be accomplished at the same time. Therefore, air pollution, climate change, and population health need to be considered simultaneously. Meanwhile, health risks from environmental factors will persist under climate change, and gaps in research evidence that may support population adaptation should be filled. In addition, innovative technologies and methodologies that may be applied to population health interventions should be developed. In summary, consideration of the health impacts and coping strategies of air pollution and climate change can help the government move forward towards sustainable development with appropriate urgency, reducing the disease burden and promoting a more healthy and sustainable future for all. CONFLICTS OF INTEREST STATEMENT Haidong Kan is an Editorial Board member of Cardiology Plus.