In this first investigation of the association between joint exposure to air pollution and residence in an ethnic enclave and GDM risk, we found evidence that residence within an ethnic enclave may mitigate negative consequences of environmental exposures, particularly VOC. In line with evidence of an association between preconception and first trimester exposure to air pollution and increased risk of GDM(12, 28, 67–69) as well as evidence of lower risk of GDM among women residing within ethnic enclaves(11, 17, 18) we found evidence that residence in enclaves is associated with lower GDM risk, regardless of VOC level.
The observations suggest chronic exposure to residence outside of ethnic enclaves and VOCs are associated with increased GDM risk for API mothers, as risks appear consistent across preconception and first trimester exposure windows. Previously among women in the CSL, we have observed consistent increases in GDM risk across preconception and first trimester exposure windows for criteria air pollutants such as nitrogen oxides and sulfur dioxide(28), as well as VOCs.(12) Similar observations of chronic exposure to criteria air pollutants and GDM were observed among women in Denmark, Sweden, and Taiwan.(67–69) Given that air pollution and ethnic enclave exposures are likely chronic, the development of GDM is likely not due to an acute exposure in pregnancy.
As ethnic enclave residence appears to mitigate the negative consequences of VOC exposure, these observations suggest immunologic response to air pollution may be an important factor. The normative immunologic response to air pollution, including during pregnancy(27), induces pro-inflammatory responses evidenced by heightened cytokine production and serum c-reactive protein levels. (27, 32, 37–40) Exposure to chronic stress leads to excessive release of stress hormones resulting in physiologic dysregulation, including impaired immune function, and consequent excessive inflammation.(42, 43) Evidence of potential physiologic dysregulation and impaired immune function in regards to ethnic enclaves is seen among Hispanic women, as those residing in non-enclave areas have higher risk of increased allostatic load, which incorporates immune function, compared to those residing in ethnic enclaves.(20) Impaired immunologic function may respond to air pollution exposure with excessive inflammation, resulting in excessive release of pro-inflammatory cytokines and damage to healthy cells, which in turn can lead to insulin resistance, a precursor to metabolic disease.(41, 42) Thus, the similar systemic inflammatory and oxidative stress responses between exposure to chronic stress and exposure to air pollution may explain the synergic effects between residence in non-enclave areas and exposure to high levels of VOCs.
Our findings are also in line with evidence suggesting that the deleterious effect of air pollution on health is stronger among those residing in more stressful contexts. For instance, air pollution exposure during the first year of life is associated with increased risk of childhood asthma, but only among children in high poverty areas.(70) Additionally, exposure to high levels of air pollution is more strongly associated with poor cardiometabolic health among adolescents residing in high-poverty areas compared to those residing in low-poverty areas.(71) It is noteworthy that the observed GDM risks were independent of individual-level proxies of health insurance and marital status, suggesting residence in an ethnic enclave may buffer the negative consequences of exposure to high levels of air pollution.
Our observations highlight the importance of focusing on API communities in environmental health research. API communities are often identified as ‘model minorities’ due to higher socioeconomic status compared to other non-white racial/ethnic groups in the U.S., suggesting API communities have favorable health outcomes compared to other racial/ethnic groups.(6, 9) Reliance on the ‘model minority’ label, in addition to API encompassing approximately 6 percent of the U.S. population, contributes to limited representation of API populations in national datasets, poor recognition of disparities among API populations, and a lack of environmental justice research targeting API communities.(6–9) The lack of relevant data excludes API communities from environmental health policy and health promotion planning when they may be an at-risk group.(7, 9) Given known health disparities and adverse environmental exposures among API communities, environmental justice research should increase efforts to better address disparities impacting API communities.
In order to address persistent racial/ethnic health disparities in the U.S. API communities should lead culturally-specific efforts to jointly improve social and environmental conditions. Previous attempts to improve environmental conditions have failed when a community’s cultural considerations have not been taken into account, resulting in worse environmental conditions and rapid displacement and gentrification.(72–74) API communities in California have been successful in community-led efforts to assemble multisector coalitions to implement environmentally friendly transportation and infrastructure improvements, affordable housing developments, and economic vitalization that reflect cultural values of communities.(72) However, further research is warranted to better understand the population-health benefits of these community-led efforts.
Our findings are notable for several reasons. First, to the best of our knowledge, this is the initial investigation of joint exposure to air pollution and residence in an ethnic enclave among pregnant women. The observations that residence within an ethnic enclave mitigates air pollution suggest chronic exposure to low or high stress prior to pregnancy has important physiologic implications during pregnancy. Secondly, this study expands our understanding of complex socioenvironmental exposures among an understudied minority population. API communities are at greater risk for high air pollution exposure, and are typically concentrated within urban areas in the U.S. Lastly, this study benefits from a large amount of clinical data for a large sample of API women in the CSL. This allows for a robust examination of community-level risk factors for GDM, a condition that disproportionately affects U.S. API women.
These findings are best considered in the context of the study’s limitations. Our measure of ethnic enclaves has not been validated in studies outside of the CSL,(11) yet was informed by attempts to capture geographic and social distinctions of ethnic enclaves. API women in the CSL are aggregated into a single category, not allowing us to examine API women by ancestry. Due to this, we used the aggregated API census data to measure ethnic enclaves. This limits our observations as API ancestry may be related to GDM risk,(18) and air pollution exposure,(6, 75) and effect of ethnic enclave residence may differ by API ancestry.(17, 18) However, previous analyses suggest the API population of metropolitan areas represented in the CSL is over 93% women of Asian ancestry with relatively few Pacific Islander women.(12) The CSL lacks maternal residential history, limiting our understanding of length of exposure to ethnic enclaves. However, most residential relocation during pregnancy occurs with a similar geographic area, and cross-sectional data allows for an approximate understanding of chronic exposures to community-level factors.(76)
VOC exposure was averaged over HRRs in which the birth occurred and was not based on participant residence. Exposure misclassification may occur if mothers resided outside the HRR for all or part of their pregnancy. However, while 10–30% of pregnant women change residence during pregnancy, most move to an area of similar level of air pollution.(77, 78) Misclassification may also be a function of local mobility and activity patterns of pregnant women. While the CSL does not have local mobility or daily activity data, current evidence suggests pregnant women and a general population comparison group both spent approximately 15 hours per day indoors.(79) Additionally, during the first trimester of pregnancy, exposure estimates based on residential address are strongly correlated with exposure estimates accounting for daily activities (r = 0.98, p < 0.01).(80)