This study evaluated the short-term effects of PM2.5 exposure on cardiovascular disease incidence from 1 January 2014 to 31 December 2019 in Yantai. We found that the PM2.5 concentration was positively associated with cardiovascular disease incidence. Every 10 µg/m3 increase of PM2.5 was associated with 0.147% (95%CI: 0.008–0.286) increase in risk of cardiovascular disease incidence, and the largest effect on cardiovascular disease incidence was found at a lag of 2 days for PM2.5. We found that females (as compared to males) and residents aged 60-75years-olds (as compared to < 60-year-olds and > 75-year-olds) were relatively more susceptible to cardiovascular disease that are related to PM2.5 pollution, and residents are more vulnerable to suffering from acute myocardial infarction. In the multi-pollutant model, the PM2.5-exposed estimated effects were higher than in the single PM2.5 pollutant model.
The short-term PM2.5-exposed effects were proved to be slightly associated with cardiovascular disease incidence, which is consistent with several previous studies(Ma, Yang et al. 2019, Kim, Lee et al. 2020). Previous studies have proved an incremented risk of 3% in the incidence of cardiovascular disease [95%CI = 1.016, 1.036] and the Hazard Ratio (HR) for acute myocardial infarction (AMI) was 1.031 [95%CI = 1.005, 1.057](Jalali, Karbakhsh et al. 2021), 4% increase in the incidence of total cardiovascular disease [95%CI: 0%-9%] and 10% increase in ischemic heart disease [95%CI: 4%-16%] for the previous 5 years(Kim, Lee et al. 2020), the relative risk of the incidence of ischemic heart disease was 1.023 [95%CI:1.007–1.040](Ma, Yang et al. 2019), the outpatient volume of cardiovascular disease of Beijing increased by 0.74%, the relative risk of angina as a chief complaint was 1.007 [95%CI: 1.003–1.012] and total respiratory outpatient visits[RR = 1.001, 95%CI: 1.000-1.002](Guangxi, Haitao et al. 2017) in cardiovascular disease for every 10 µg/m3 increase of PM2.5. The results found a slightly weaker effect between PM2.5 and the incidence of cardiovascular disease. An explanation may be that, instead of choosing certain specific subgroups, this study introduced the whole population which might lead to a more general result. Another explanation may be that the coastal region has a lower estimated effect of exposure on pollution compared to the other regions(Sinclair and Tolsma 2004). Furthermore, the difference in the value of the risk effect may be due to the difference in sources and components of pollutants in countries and regions, the regional economic level, and the local pollution status(Cao, Lv et al. 2014, Zhang, Shao et al. 2019) .
In terms of stratified analysis, we found that females were more vulnerable to cardiovascular disease occurrence associated with PM2.5 contamination(Gong, Sun et al. 2019). Studies have confirmed that due to increased pulmonary particle deposition and high airway reactions(Kan, London et al. 2008), and the female are more sensitive to indoor contamination from kitchen lampblack and other sources(Smith, Bruce et al. 2014, Bruce, Pope et al. 2015). In addition, women generally receive less attention to their health from the family and society level, which also may lead to a higher risk of cardiovascular disease occurrence in female than male. As for age subgroups, people aged 60–75 years are more sensitive to PM2.5 than the other subgroups. RR for cardiovascular disease incidence peaked at a lag of 4 ,0 and 0 day(s) for the aged below 60 years, 60–75 years, and above 75 years subgroups respectively. It suggests that older elderly(aged above 60 years) are more sensitive to PM2.5 exposure, which can increase the risk of cardiovascular disease in the elderly. Moreover, the 60–75 years subgroup has the highest estimated effects risk, which suggests that the elderly subgroup is most likely to increase their risk of cardiovascular disease(Ma, Yang et al. 2019). It is similar to the findings of Bautista’s study(Bautista 2019). The older residents were accompanied by physiological hypo-function as the growth of age(Analitis, Katsouyanni et al. 2006, Bellavia, Urch et al. 2013). The previous finding suggests that exposure to PM2.5 can impair cardiovascular function in elderly people(Bruce, Pope et al. 2015), who are more susceptible, even if the concentration of PM2.5 was lower than 10 µg/m3. In addition, the youth and middle-aged adults (the age below 60 years) have to work or study outdoor and would be difficult to avoid exposure, contributing to the degree of higher risk effect of cardiovascular disease. In contrast, the elderly aged above 75 years will consciously avoid going outside in severe pollution weather and could reduce their exposure to air pollution(Analitis, Katsouyanni et al. 2006). In terms of disease categories subgroups, elevating PM2.5 concentrations leads to an increased risk of acute myocardial infarction in residents(Mustafić, Jabre et al. 2012, Wang, Zhang et al. 2016). Furthermore, the case of myocardial infarction is far greater than the coronary heart disease, along with large RR, indicating that the myocardial infarction incidence has a higher risk in populations with the same degree of contamination(Zang and Qi 2017, Farhadi, Abulghasem Gorgi et al. 2020). It was found that inherent risk factors like age, gender, and family history could not be regulated, but some risk factors such as environmental air pollution and unhealthy lifestyle are largely preventable(Kiani, Hesabi et al. 2016, Bhandari, Singh et al. 2017, Rathore, Singh et al. 2018).
Our study has several public health implications. Our study extended the evidence of adverse effects of PM2.5 exposure on cardiovascular disease incidence and found that the elderly aged 60–75 years and female are sensitive to PM2.5 exposure, which provides evidence to make environmental and health intervention policies. Firstly, the government and enterprises should pay more attention to PM2.5 air pollution in the future, the government should develop detailed industrial emission standards, and enterprises innovative industrial waste gases technologies to protect vulnerable populations(Han, Xu et al. 2021, Han, Xu et al. 2021). In addition to strategies at the government level, we should take female and the elderly into key consideration to implement the tertiary prevention of cardiovascular diseases, enhance the residents’ recognition of the risk of air pollution on cardiovascular diseases through community interventions, conduct early warnings of severe polluted weather, and reduce exposure to polluted weather for vulnerable populations.
The present study has several advantages. Firstly, the study estimates the effects of short-term exposure to PM2.5 on cardiovascular diseases incidence cases instead of cardiovascular disease-related hospitalizations and mortality, which can avoid the interference of prognostic factors and disease conditions effectively(Pearson-Stuttard, Buckley et al. 2021); incidence can measure the counts of new cases which can accurately reflect the effect of air pollution exposure as a pathogenic factor on the occurrence of cardiovascular disease(Kim, Lee et al. 2020); the effects estimated by cardiovascular diseases incidence exposed to pollution provide evidence on guide primary prevention. Secondly, previous researches have discussed the risk of short-term exposure to PM2.5 on cardiovascular disease-related hospitalizations and mortality, and few studies discussed associations between short-term exposure to PM2.5 and cardiovascular diseases incidence. Therefore, this study analyzes the relationship between short-term exposure to atmospheric PM2.5 and cardiovascular disease incidence to fill the theoretical gaps, so as to comprehensively evaluate the health effect of PM2.5 pollution on cardiovascular diseases. Finally, Yantai is a coastal city with a maritime climate of gentle moisture. The air quality is higher when the sea breeze is transported, and the sea-land breeze circulation is closely related to the ambient pollution and plays an important role in the dilution and diffusion behavior of pollutants in the atmosphere, thus, the results may also enable analogy to countries and regions with similar climates(Fishman, Iraci et al. 2012).
Inevitably, there are also several limitations in this study. Firstly, the population PM2.5 exposure level in the study used the average data of outdoor fixed monitoring points, ignoring such penetration of ambient pollutants to indoor spaces and indoor pollution sources, which could not reflect the accurate ambient pollution exposure level of individuals. Secondly, the classification of cardiovascular disease types was possibly not accurate enough, and parts of cardiovascular disease subgroups were not monitored in city-level systems, so other subgroups' effects may be underestimated. Finally, the socioeconomic information on the individual level such as the potential risks of cardiovascular diseases, residence and career, were not introduced into the analysis due to the limit of data. It is difficult to avoid the deviation, so further studies are warranted.