Cardiovascular disease disparities across ethnicity and intersecting socioeconomic positions: The role of air pollution and green space

Cardiovascular diseases (CVD) are responsible for an enormous disease burden worldwide. Minoritized ethnic populations generally face higher CVD risks than majority populations, although these risk differences vary significantly among ethnic groups. Additionally, individuals in lower socioeconomic positions consistently have a higher CVD risk compared to those in higher socioeconomic positions. This thesis investigated how air pollution and green space exposures contribute to inequalities in ischemic stroke and ischemic heart disease across ethnic groups and at the intersection of ethnicity and socioeconomic position.

Chapter 2 provides a scoping review on ethnic disparities in exposure to air pollution in high-income countries. This review reveals disparities in air pollution exposure among ethnic groups in high-income countries to the detriment of minoritized ethnic groups.

Chapter 3 presents a nationwide analysis of air pollution exposure in the Netherlands across the 40 largest ethnic groups and three socioeconomic groups. Results show that minoritized ethnic groups experience consistently higher pollution levels than the ethnic Dutch population, with substantial variations among minoritized groups. Disparities persist even after adjusting for socioeconomic position. Policies to address these inequalities should prioritize emission reductions from multiple sources, including vehicular and industrial emissions.

Chapter 4 explores the use of urban green spaces by women from Turkish and South Asian Surinamese backgrounds living in disadvantaged neighborhoods in Utrecht and The Hague. Using six focus group discussions, the study identifies motives, means and prerequisites to visit green space, covering four interacting themes: social, personal, environmental characteristics and activities. Socializing was an important motive to visit green space. Personal motives mainly consisted of positive effects on mental and physical well-being. Activities undertaken in green space were often a means to socialize or improve well-being. Many environmental factors, including safety, aesthetics, and (sanitary) facilities, influenced motivation to visit green space. The possibility of expanding the multifunctionality of green spaces to provide marginalized populations with more equitable access and activities should be further explored.

Chapter 5 evaluates differences in the relationships between air pollution exposure and ischemic stroke or ischemic heart disease (IHD) among six ethnic groups in the Netherlands. Results revealed notable ethnic differences in associations. For ischemic stroke, the hazard ratio of increasing NO2 for ischemic stroke was lowest for Moroccans and highest for Turks, with similar patterns observed for PM2.5. Unexpectedly, for IHD, higher air pollution exposure was associated with lower incidence in some groups, with the lowest HRs observed for Turks and the highest for Surinamese and Dutch populations. Policies to reduce air pollution and prevent ischemic stroke should target populations vulnerable to air pollution with a high cardiovascular disease risk.

Chapter 6 investigates the extent to which air pollution exposure mediates ischemic stroke disparities between Indonesian, Surinamese and Dutch Caribbean populations compared to ethnic Dutch. For Surinamese, NO2 exposure mediates 13.8% and PM2.5 mediates 7.9% of the difference in ischemic stroke occurrence compared to ethnic Dutch. For Dutch Caribbeans, NO2 mediates 14.7% and PM2.5 mediates 8.0%. These results underscore the urgent need for air pollution reduction strategies to reduce the disproportionate ischemic stroke burden in Surinamese and Dutch Caribbean populations.

Chapter 7 discusses the importance of centralizing environmental justice in cardiovascular research to address health disparities across ethnic and socioeconomic groups. It highlights the severe underrepresentation of minoritized ethnic populations in European research cohorts and the limitations of registry data for environmental justice research, which often lack the richness needed to account for diverse CVD risk factors. A balance between large sample sizes and detailed data is necessary to accurately assess differences across subgroups. The chapter calls for more representative data through harmonizing registries across countries and prospectively collecting data in diverse settings.