Intersectionality and Cognitive Weathering: a Growth Curve Analysis of Mid- to Later-Life
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Intersectionality and Cognitive Weathering: A Growth Curve Analysis of Mid- to Later-Life Cognitive Decline Jo Mhairi Hale Max Planck Institute for Demographic Research Abstract Alzheimer‘s disease (AD) is the sixth leading cause of death in the United States, afflicting 8.8% of Whites, but a fifth of Latinx and almost a quarter of Black elders (Alzheimer‘s Association 2010). Drawing from intersectionality theory and the weathering hypothesis, I hypothesize that multiple social disadvantages intersect to cause these AD disparities. Using the Health and Retirement Study (1992-2014), I estimate growth curve models of cognitive function for elders aged 50-90 (n=30,224). Life-course socioeconomic status (SES), health behaviors, and comorbidities only partially explain racial/ethnic and sex cognitive disparities. Multiple social disadvantages accumulate to negatively affect later-life cognition. White women‘s, Blacks‘, Latinas‘, and US-born Latinos‘ cognitive function declines significantly faster that White males‘, net of controls. Life-course SES interacts with race/ethnicity and sex to affect cognitive trajectories in complicated ways, such that the applicability of theories of cumulative disadvantage, persistent inequality, or age-as-leveler depends on the subpopulation. KEY WORDS: Cognitive Function; Alzheimer‘s; Life Course; Weathering; Race/Ethnicity; Health Disparities; United States Intersectionality and Cognitive Weathering: A Growth Curve Analysis of Mid- to Later-Life Cognitive Decline Populating aging has provoked a spate of research on cognitive decline because of the growing share of the population at risk of late-life cognitive impairment, which is most commonly caused by late-onset Alzheimer‘s disease (AD) (Alzheimer‘s Association 2016). AD has significant racial/ethnic, sex, and socioeconomic status (SES) disparities. In the U.S., AD afflicts 5.4 million people (Alzheimer‘s Association 2016). Whereas it is 8.8% of White elders, it is a fifth of Latinx and almost a quarter of Black elders (Alzheimer‘s Association 2010). Though sex disparities are often attributed to female‘s longer life expectancy, research cannot yet explain why at younger ages females‘ prevalence is 16% to males‘ 11% (Fargo, Bleiler, and Mebane- Sims 2009). In terms of SES, individuals with less than a high school education have significantly higher prevalence and incidence than those with at least a high school diploma, and those with lower occupational attainment have over twice the risk of those with high occupational attainment (Meng and D‘Arcy 2012; Stern 2012). However, challenges inherent in life course research (Kuh et al. 2003) mean gaps remain in understanding social predictors of AD. Little research has addressed cognition from an intersectional perspective (Hulko 2004 for an exception). Just as intersecting ascribed (e.g., race/ethnicity, sex) and achieved (e.g., education) characteristics predict a range of life chances, I propose positionality on multiple axes of social stratification affects risk of cognitive decline.1 Social positionality affects health outcomes through structuring access to resources (Phelan, Link, and Tehranifar 2010). But, racism and sexism shape lives beyond that, including subjecting People of Color (POC) and women to chronic stressors (Collins 2015; Das 2013; Phelan and Link 2015; Williams 2012). 2 Geronimus‘s weathering hypothesis proposes that socially-disadvantaged individuals experience accelerated aging due to carrying higher allostatic load (Geronimus et al. 2015; Geronimus and Korenman 1992). ―Allostatic load‖ is the level of physiological dysregulation believed to be caused by chronic or recurring stressors (Juster, McEwen, and Lupien 2010; Seeman et al. 2010). I extrapolate that those who occupy multiple disadvantageous positions will experience faster cognitive decline, which I term ―cognitive weathering.‖ I derive hypotheses from intersectionality theory and the weathering hypothesis to evaluate how social factors, including race/ethnicity, sex, life-course SES, behavior, and health factors, intersect to affect later-life cognitive function and rate of cognitive decline. In other words, to what degree are these racial/ethnic and sex disparities explained by socially-patterned exposures, such as the unequal distribution of education and poverty (Stern 2012; Zhang, Hayward, and Yu 2016)? I posit that the residual disparities may be related to POC‘s and women‘s higher allostatic load. Using the Health and Retirement Study (1992-2014), I estimate growth curve models of cognitive function for elders aged 50-90 (n=30,224), specifically considering the cumulative disadvantage/inequality, persistent inequality, and age-as-leveler hypotheses. My findings provide clear evidence for the importance of intersectional approaches. Background Alzheimer’s prevalence by sex, race/ethnicity, and SES Current research shows associations between AD and sex, race/ethnicity, and some SES, behavioral, and health factors. Two-thirds of those with an Alzheimer‘s diagnosis are females, partially because they have longer life expectancy than males, i.e. males die before they are diagnosed and/or longer-living males possess protective factors (Resnick and Driscoll 2007). Yet, taken at the same age, females‘ prevalence is still 5% higher (Alzheimer‘s Association 2015). Recent research suggests female carriers of a genetic risk factor (ApoE-ɛ4) may be at 3 higher risk of AD, as well as experiencing greater symptom severity (Mazure and Swendsen 2016). Although medical researchers continue to search for biological determinants for these disparities (Altmann et al. 2014; Zhao et al. 2016), cognitive differences are likely also rooted in social structures. For example, women over age 65 average less education (negatively associated with AD) than men (Siegel 2011; U.S. Census Bureau 2016). I argue that, in addition to these socially-patterned disparities, the stress of living in a patriarchal, sexist society may cause cognitive weathering (Collins 2015). Among other stressors, women are more likely to be survivors of domestic and sexual violence, and they are more likely than their same- race/ethnicity male counterparts to face employment discrimination (England 2010; Krieger 2014; Pedulla and Thebaud 2015; Read and Gorman 2010). Similarly, despite evidence that POC are underdiagnosed for memory diseases, U.S. Blacks and Latinx still have higher rates of Alzheimer‘s diagnosis than Whites (1.5 to 2 times and 1.5 times, respectively) (Manton, Stallard, and Corder 1997; Steenland et al. 2015). Blacks and Latinx transition to cognitive impairment earlier than Whites and live with cognitive impairment longer (Reuser, Willekens, and Bonneux 2011). Researchers have published conflicting results on how much SES factors, health behaviors, and chronic illnesses mediate Black/White cognitive disparities (Zhang et al. 2016). But, most prevalence studies do not take life-course SES into consideration, thus it is unclear to what extent these disparities are driven by racially-patterned socioeconomic factors (Fargo et al. 2009; Reskin 2012). However, many other health disparities exist even net of SES (Hayward et al. 2000), and I suggest the stress of living in a White supremacist society may contribute to cognitive disparities beyond socioeconomic inequalities. 4 Related to other social disadvantages, researchers find significant independent effects on cognitive function of educational attainment and occupation (Richards and Sacker 2003). There are mixed results as to whether early-life SES affects later-life cognitive function (Turrell et al. 2002). Other significant early socioeconomic indicators include number of siblings and childhood area of residence (suburban/rural/urban) (Moceri et al. 2000). Education is negatively associated with AD risk and appears to delay age of clinical manifestation (cf. Siegel 2011). In the U.S., those with less than twelve years of education had a 35% greater chance of developing dementia than those with more than fifteen years of education, and those with less than eight years of formal schooling had over twice the risk of those with higher education (Kukull et al. 2002; Stern 2012). Those with higher occupational attainment had about 44% lower risk of cognitive impairment (Valenzuela and Sachdev 2006). Lower-SES is also associated with higher allostatic load (Seeman et al. 2010). Most of the above research on race/ethnicity, sex, and SES focuses on one factor, not controlling for each other or confounding variables such as health behaviors or chronic illnesses (cf. Zhang et al. 2016 for an exception). The evidence is therefore inconclusive as to how life- course social factors mediate racial/ethnic/sex disparities in cognition. These gaps in the literature motivate my first hypothesis. Hypothesis 1: Life-course socioeconomic status, behavioral factors, and chronic illnesses partially mediate racial/ethnic/sex disparities in mid- to later-life cognitive function. As intersectionality theory indicates, however, analyzing race/ethnicity, sex, and SES separately paints an incomplete picture. Social positions on multiple axes interact to influence outcomes. 5 Intersectionality theory Intersectionality theory asserts that ascribed and achieved characteristics intersect to influence opportunity structures through exposure to a particular balance of benefit and risk related to human and cultural capital in the form of ―material, relational, and lifestyle‖ factors (Warner and Brown 2011:1238). These characteristics