Neighborhood racial/ethnic segregation and cognitive decline in older adults

Highlights

• Social determinants of health affect cognition in ethnically diverse older adults.

• Residential segregation is a manifestation of historical racism.

• Segregation is complexly related to cognition at baseline and cognitive decline.

• More research is needed on complex associations of segregation with cognition.

Abstract

Social determinants of health, including neighborhood factors, play a key role in the health of diverse older adults. However, few longitudinal studies have examined the role of neighborhood racial/ethnic segregation on cognitive decline in diverse samples. We examined older non-Hispanic White (NHW), Black, and Latino participants evaluated at an Alzheimer's Disease Research Center. Neighborhood racial/ethnic segregation was measured using the Getis-Ord G_i* statistic, a spatial measure of clustering that was created for Latino and Black clustering separately. Cognitive outcomes included episodic memory, semantic memory, and executive function. We used mixed effects multivariable regression models to evaluate associations between segregation and cognitive function and decline. We had 452 individuals: 46% NHW, 26% Black, and 21% Latino in 309 census tracts with an average of 5.2 years of follow-up data (range 0.6–15.0). In analyses that adjusted for a variety of covariates (including neighborhood SES), individuals in neighborhoods with a higher clustering of Latino residents (higher Gi* statistic) had slower declines over time on semantic memory and those in neighborhoods with a higher clustering of Black residents had slower declines over time on episodic memory. In race/ethnicity-stratified adjusted analyses: for Black participants, the association between clustering and cognition was present for episodic memory and executive function, showing lower baseline scores in highly clustered Black and Latino neighborhoods, respectively. There was no association with cognitive change. Among Latino participants, highly clustered Latino neighborhoods were associated with lower baseline scores in semantic memory, but slower declines in episodic memory; Latinos living in neighborhoods with a greater clustering of Black residents also had slower declines in episodic memory. Among NHWs, residing in neighborhoods with a higher clustering of Latino residents was associated with slower declines over time on semantic memory. Segregated neighborhoods may be differentially associated with cognitive outcomes depending on individual race/ethnicity.

Introduction

The increase of both ethnically diverse and older adult populations is predicted to be significant over the coming years. Moreover, the Hispanic/Latino and Black/African American populations (henceforth Latino and Black) have been projected to grow significantly (114.8% and 63.6% respectively, between 2014 and 2060) (Colby, 2014). Given this growth in the older adult population in general, and Black and Latino adults specifically, it is imperative that we understand the risks for cognitive impairment in these populations given their higher prevalence of Alzheimer's disease (AD) (Tang et al., 1998). Many studies have denoted the individual characteristics associated with cognitive impairment related to dementia including age, education, genetics, and medical conditions such as cardiovascular disease (Hu et al., 2017; Tilvis et al., 2004). However, a growing body of research has demonstrated the important role of social determinants of health, including neighborhood racial/ethnic characteristics on older adults' general health (White and Borrell, 2011), depression (Mair et al., 2010), mortality (Warner and Gomez, 2010), and more recently-cognition (Caunca et al., 2020; Kovalchik et al., 2015). Contextual factors play an important role in health disparities but up until only recently, have been understudied in cognition. Given that some contextual factors may be modified by public health policy and intervention, it is important that their role be elucidated in AD research.

Williams and Collins (2001) posited that racial segregation, or the spatial separation of groups, is a fundamental cause of health disparities among Black populations. Segregation, one form of structural racism that existed prior to the 1960's, was pervasive and enforced by social and public policies such as the Jim Crow laws and the historical act of redlining, which directly played a role in the segregation of neighborhoods by race and socioeconomic status (SES) through involvement of the national mortgage market (Kimble, 2007; Kushner, 1979). Neighborhoods that are segregated and thus disenfranchised experience higher levels of poverty and policing/crime. When certain groups of people are systematically placed into environments that are exposed to higher levels of policing/crime, individuals tend to socially isolate from each other which limits their interactions (Massey and Denton, 1993). The limitation on diverse social interactions, in turn, inhibits potential for cognitive growth and stimulation. Segregation has created distinct social environments in that most poor Black adults reside in neighborhoods of concentrated poverty (Williams and Collins, 2001). Similarly, Latinos are disproportionately exposed to neighborhood disadvantage, which may have detrimental consequences for their health (Firebaugh and Farrell, 2016; Do et al., 2017). Oftentimes, concentrated poverty is linked to poor cognitive functioning due to the lack of resources like higher quality education, access to health care, better job opportunities, healthy grocery stores (including fresh produce), and safe recreational and greenspace areas, all of which can impact health and cognition (Ertel et al., 2008).

On the other hand, residential segregation may lead to ethnically clustered neighborhoods, or ethnic enclaves, characterized by high social capital or cohesion (Ostir et al., 2003; Shaw and McKay, 1942). This theoretical perspective assumes a positive effect of living within a neighborhood characterized by a high concentration of individuals from similar backgrounds through the creation of social networks and the diffusion of positive cultural practices (Eschbach et al., 2004a; Aneshensel and Sucoff, 1996; Lee and Ferraro, 2007; Patel et al., 2003). At the neighborhood level, social capital is composed of collective resources accessible to groups of people within a social structure that allows for achieving common goals (Rostila, 2011). Ethnically homogeneous Latino neighborhoods are associated with higher self-rated health (Patel et al., 2003), lower risk of mortality (Eschbach et al., 2004b; LeClere et al., 1997; Bond Huie et al., 2003), fewer depressive symptoms (Ostir et al., 2003; Aneshensel and Sucoff, 1996), and healthier dietary habits (Lee and Cubbin, 2002). In Philadelphia, Black mortality was lower among residents of predominantly Black neighborhoods with high neighborhood social capital in comparison to Black residents living in predominantly White neighborhoods (Hutchinson et al., 2009). It may be that residents in ethnically homogeneous neighborhoods benefit from shared psychosocial resources, social organization and control, preservation of culture, common language, and healthful traditional behavioral norms (Ostir et al., 2003; Patel et al., 2003; Eschbach et al., 2004b; Lee and Cubbin, 2002), as well as high rates of labor force participation, intact family structures, home ownership, and residential stability (Moore, 1989). Latino and Black residents living in homogeneous neighborhoods were more likely to use health care services than those living in heterogeneous communities (Haas et al., 2004). This collective capital may contribute to better cognitive health (Glymour and Manly, 2008).

These two theoretical perspectives and subsequent predicted outcomes may vary because of the different ways that segregation has been measured. There are formal measures of segregation, namely evenness, exposure, concentration, centralization, and clustering (Massey and Denton, 1988). Evenness captures the level of differential spatial distribution of groups: racial/ethnic minorities are overrepresented in some areas and underrepresented in others. Exposure refers to the probability of interacting with other groups. Concentration measures the physical space inhabited by certain groups. Centralization indicates the degree to which a group is located at the center of an area. Finally, clustering refers to the level that groups might form one large contiguous enclave, or be scattered widely around the urban area. Then, there are proxies of segregation, such as racial/ethnic composition of neighborhoods. Segregation and composition are conceptually different (Lee et al., 2014). The former relates to how two or more groups distribute spatially across neighborhoods within a large area (e.g., a metropolitan area), whereas the latter refers to the relative size of racial/ethnic groups in an area (i.e., racial composition). It is important to distinguish these categorizations in empirical studies of residential segregation. We highlight the different ways that segregation has been assessed to provide a context for understanding studies on segregation and health outcomes.Aneshensel et al. (2011)

Using data from the Health and Retirement Study (HRS), Aneshensel et al. (2011) showed that late middle-aged adults living in highly segregated Black communities had poor cognitive function at baseline; however, this was the case only if they had low education. In contrast, the highest level of cognitive functioning was among highly educated persons who lived in predominantly Black neighborhoods. In that study, racial/ethnic segregation was operationalized as the proportion of residents who were Black and proportion of residents who were Latino. Kovalchik et al. (2015) expanded on this work by using multiple waves of HRS data and by examining both informal (census tract racial/ethnic composition) and formal (county-level isolation index) measures of segregation. They found that both Latino composition and segregation were positively correlated with cognitive function (cognition at baseline) and negatively correlated with cognitive decline (cognition over time) for all older adults- NHW, Black, and Latino. The cross-sectional finding suggested that there may be higher levels of social integration and cultural resources that protect people, regardless of their race/ethnicity, in Latino communities (Scarmeas and Stern, 2003). The longitudinal finding, however, showed a steeper rate of decline (over time) in these neighborhoods. Recently, Caunca et al. (2020) examined life-course or long-term residential segregation of Black participants in CARDIA. They found that the longer Black participants were segregated in young adulthood, the worse their processing speed was in midlife.

Given the paucity of longitudinal studies on cognition, it is unclear how residential segregation is associated with cognitive trajectories of its diverse residents. The goal of this study is to examine the association of neighborhood segregation on cognitive function (cross-sectionally as measured at study baseline) and cognitive decline over time in a diverse cohort of older NHWs, Latinos, and Blacks. We add to the literature on neighborhood and cognition by considering the impact of racial/ethnic segregation and contrasting the potential effects of segregation and ethnic enclaves. Moreover, the cognitive outcomes of living in distinct neighborhoods may impact residents differently, as posited by the ecological framework principle-that the same environment has systematically different effects on people depending upon their personal characteristics (Bronfenbrenner, 1979). Given these unique individual-environment interactions, we additionally stratify our analyses based on individual race/ethnicity. Thus, we hypothesized that greater neighborhood segregation would be associated with baseline cognition and change in cognition over time and that the associations would vary by race/ethnicity. However, relevant prior studies and theoretical underpinnings are currently insufficient to hypothesize specific directions for the associations.