An analysis of trends in the burden of ischemic stroke caused by air pollution in China between 1990 and 2021 | BMC Public Health

Research findings indicate that from 1990 to 2021, the ASMR and ASDR of ischemic stroke attributable to air pollution generally exhibited a downward trend, with AAPC of -1.99% and -2.02%, respectively. However, compared with women, the decline in ASMR and ASDR among men has been slower. The analysis using the Joinpoint regression model indicates that, while the ASMR and ASDR for men and women have varied over the past 32 years, they have consistently decreased over the last decade. Notably, in the past three years, the decline in ASMR and ASDR for men has been slower compared to women. It is important to highlight that the disease burden of ischemic stroke is particularly significant among the elderly, especially among men aged 70 and above. According to the decomposition analysis, epidemiological changes play the leading role in reducing deaths and DALYs from ischemic stroke, while population growth and aging have contributed opposing forces to these trends.The ARIMA model prediction analysis suggests that over the next 15 years, the ASMR and ASDR of ischemic stroke attributable to air pollution among women will continue to decline. In contrast, the ASMR among men will continue to rise, and the ASDR will initially increase slowly before stabilizing. Although the overall disease burden of ischemic stroke attributable to air pollution has shown a downward trend, the disease situation remains severe, particularly for men, especially elderly men.

Joinpoint regression analysis indicates that the ASMR and ASDR of ischemic stroke attributable to air pollution in China have shown a downward trend in recent years, consistent with the overall trend in the disease burden of ischemic stroke [21]. This suggests that the current measures taken by China to improve air quality and reduce pollutant emissions are effective. Evidence from studies suggests that both brief and prolonged exposure to air pollution can heighten the risk of ischemic stroke. The underlying mechanism may involve environmental PM2.5 exposure contributing to the formation of atherosclerosis, which affects both cerebral small vessels and large arteries, thereby increasing the risk of ischemic stroke [8, 9, 22, 23]. Studies have further indicated that ischemic stroke caused by PM2.5 exposure is connected to systemic inflammation and oxidative stress, which elevate reactive oxygen species (ROS) levels and decrease anti-inflammatory capabilities, thus raising the risk of thrombosis [24]. Additionally, PM1 and O₃ pollutants are also linked to the occurrence of ischemic stroke. Small rises in air pollution levels are associated with a greater likelihood of developing cerebrovascular diseases. This is because these pollutants can damage the vascular endothelium, activate the sympathetic nervous system, and adversely affect blood circulation [25]. In recent years, with the growing public awareness of air pollution and the continuous improvement of environmental protection laws, various air pollutants have exhibited a decreasing trend annually [26, 27]. While China has achieved remarkable progress in enhancing air quality, the burden of ischemic stroke due to air pollution remains significant, and sustained initiatives are still essential.

Our findings indicate that the impact of air pollution on ischemic stroke is more pronounced among men than women in China, especially during the last decade and for men aged 70 and over.The primary contributor to this burden is PM2.5 from air pollution. Inhaled pollutants can disrupt the homeostasis of the autonomic nervous system (ANS), leading to increased vascular resistance [28]. Studies have shown that when environmental PM2.5 concentrations are between 0 and 35 μg/m³, men exhibit greater sensitivity to fine particulate matter exposure compared to women. Additionally, elderly individuals are more susceptible to PM2.5 exposure than younger populations [29]. Studies have also found that short-term exposure to PM2.5 in older adults is associated with increased cerebral vascular resistance and diminished cerebral blood flow [30]. Therefore, it can be inferred that elderly men are more sensitive to air pollution. Air pollution increases the risk of various diseases in elderly men, including cardiovascular and cerebrovascular diseases, as well as respiratory diseases. Consequently, during periods of high air pollution, elderly men should minimize outdoor activities and actively wear masks to protect their respiratory and cerebrovascular health.

According to our decomposition analysis, the principal force driving the decrease in ischemic stroke mortality and DALY rates is epidemiological change. This indicates that the implementation of air pollution control policies and the reduction of anthropogenic pollutant emissions have significantly improved air quality [26], thereby reducing the disease burden of ischemic stroke. However, with the aging of the population, the cerebral blood flow in elderly individuals will decline, increasing their susceptibility to air pollution and, consequently, the risk of ischemic stroke. This finding is consistent with previous research [29, 30]. Population growth and aging are expected to lead to increases in mortality and DALY rates, necessitating continuous public health interventions that prioritize prevention, early diagnosis, and effective treatment to address this growing concern.

The ARIMA model projects that, over the next 15 years, the ASMR and ASDR of ischemic stroke linked to air pollution will continue to drop among women in China, while among men, these rates are anticipated to rise steadily. These trends suggest an enhanced health awareness among the female population, including healthier lifestyles and improved disease prevention measures. The reduction in the burden on women is a positive development, reflecting the positive impact of improvements in air quality and ischemic stroke management. Differences in health awareness and behavior between men and women may contribute to these divergent trends. For instance, unhealthy habits such as smoking are more prevalent among men. The increased burden suggests that there is a need to enhance public awareness of the health risks posed by air pollution, particularly among the male population, in order to promote healthier lifestyles and stronger environmental protection consciousness. In response to this burden, improving air quality is crucial. The government can strengthen supervision over environmental protection and mobilize all sectors of society to actively participate in atmospheric environment protection, thereby reducing the impact of air pollution on public health, especially for the male population.

However, the ARIMA model relies on several key assumptions that may influence the accuracy of its predictions. First, it assumes that the time series data are stationary, meaning that statistical properties such as mean and variance do not change over time [31]. This assumption could be problematic if the data show long-term trends or abrupt changes in external conditions, such as air pollution control policies or economic shifts. Second, ARIMA assumes that the error terms in the model are normally distributed and independent, but real-world data often contain autocorrelations or external shocks that violate these assumptions [32]. For example, public health crises like the Coronavirus disease 2019 (COVID-19) pandemic or significant policy changes can introduce biases. To address these limitations, we performed sensitivity analyses to test the robustness of our predictions by varying key assumptions and comparing different model specifications. This process ensures that our findings are not overly dependent on any single set of assumptions or external factors.

Social, cultural, and biological factors behind gender and age differences

Evidence suggests that the burden of ischemic stroke attributable to air pollution is disproportionately higher among men, particularly older men. These gender differences can be attributed to a combination of biological and sociocultural factors. Biologically, men are at greater risk for ischemic stroke due to differences in cardiovascular risk factors, such as higher rates of smoking and alcohol consumption [33,34,35]. These factors increase their susceptibility to stroke, especially in the presence of environmental pollutants like PM2.5 [29]. Additionally, older adults, especially men, tend to have a higher prevalence of chronic conditions such as hypertension, diabetes, and atherosclerosis, making them more vulnerable to the adverse effects of air pollution [36,37,38]. Socioculturally, men are more likely to engage in outdoor activities that increase their exposure to air pollution, including occupational exposure, which is often higher in male-dominated industries [39]. Furthermore, older men may have more limited access to healthcare and resources to mitigate the effects of air pollution, such as air purifiers or appropriate medical interventions.

These biological and sociocultural differences explain why men, particularly elderly men, are more severely affected by air pollution than women. The aging process itself exacerbates the risks associated with environmental pollutants due to reduced physiological resilience and the accumulation of chronic health conditions. Therefore, gender and age differences in health outcomes are shaped not only by biological mechanisms but also by broader social determinants, including lifestyle choices, socioeconomic status, and healthcare access [40,41,42].

Public health policy recommendations

The ARIMA model projects that, over the next 15 years, the ASMR and ASDR of ischemic stroke linked to air pollution will continue to drop among women in China, while among men, these rates are anticipated to rise steadily. These trends suggest that public health interventions, particularly those targeting women, may be more effective in raising health awareness and improving health behaviors. The decrease in the disease burden among women can be attributed to increasing health awareness, healthier lifestyles, and more proactive disease prevention measures [43]. However, the rising burden among men calls for intensified health education campaigns specifically targeting male populations, particularly older men.

Our findings underline the need for a more tailored approach to public health interventions. For instance, government policies should prioritize air quality improvements, but with a specific focus on vulnerable populations such as elderly men [44]. Health education campaigns should raise awareness of the risks of air pollution and promote protective measures such as reducing outdoor activities during high pollution periods and wearing masks [45, 46]. Furthermore, policymakers should consider gender-specific interventions that address the unique risks faced by men, particularly in occupational settings, and ensure that healthcare systems are equipped to support elderly individuals with chronic conditions that exacerbate the effects of air pollution.

Limitations and future research directions

Although GBD 2021 employed rigorous algorithms to estimate the data, the study inevitably faces some limitations. Firstly, the GBD 2021 dataset is limited to national-level data and does not provide more detailed information at the provincial or municipal levels. The use of finer-grained classification data would help reveal regional differences more accurately. Secondly, due to challenges in accurately recording deaths caused by ischemic stroke and distinguishing them from other causes, the statistical data on the disease burden of ischemic stroke attributable to air pollution may be underestimated. Thirdly, predictions are based on specific assumptions, while the occurrence of diseases is influenced by multiple unpredictable factors, including population dynamics, environmental conditions, healthcare services, and economic conditions. Therefore, the prediction results may be subject to bias. It is necessary to further refine the ARIMA model to enhance its predictive accuracy.