The Role of Cumulative Advantage/Disadvantage in Disparities in Alzheimer's Disease Risk

Abstract

BACKGROUND: Substantial disparities have been observed in Alzheimer’s disease (AD) by race and social class. The persistence of health disparities over time and for diseases with distinct etiological processes suggests that the fundamental cause may reside within processes of advantage and disadvantage that accumulate across the life course. Although education is a well established risk factor for AD, it is unclear if the mechanistic role of education in AD disparities is through direct cognitive stimulation – the most commonly accepted hypothesis in AD research – or if it operates indirectly as a marker of social status and discrimination. OBJECTIVES: This dissertation aims to answer the question of how social processes at different points in the life course produce socioeconomic and racial inequalities in Alzheimer’s disease risk. This question is broken into a series of three studies that examine the existing evidence for the role of modifiable risk factors in AD, and test for the role of cumulative advantage/disadvantage in the context of socioeconomic, and racial disparities. METHODS: Study one is a structured narrative review of studies that tested for differences by race of the effect of any of six modifiable risk factors (education, obesity, smoking, physical activity, social isolation, and psychosocial stress) for AD risk. Study two used a Generalized Estimating Equation to examine the effect of individual SES and state-level income inequality on Subjective Cognitive Decline, as reported in the Cognitive Decline module of the Behavioral Risk Factor Surveillance System. Study three used structural equation modeling to conduct mediation and conditional process analysis (moderated mediation) to examine the role of markers of socioeconomic status and stress in racial disparities in AD risk among participants of the National Social Life Health and Aging Project. RESULTS: Of 3,464 identified studies in study one, 45 tested for differences in the modifiable risk factors by race. Education was the most widely examined risk factor, and the only factor in the review with strong evidence for a role in racial disparities. In study two, a dose-response effect was observed for income while those with high school education reported better cognition than those with some college. State-level income inequality was not associated with cognitive decline. In study three, education consistently mediated the race-cognition pathway, and perceived stress and assets mediated the education-cognition pathway. In all models, the direct effect of race on cognition remained large. CONCLUSIONS: Combined, these studies confirmed the importance of education for socioeconomic and racial disparities in AD risk, but suggested that education operates as an indicator of social status and discrimination, as well as through its role via cognitive stimulation. These findings point to the importance of considering social factors from across the life course in public health research and interventions aiming to understand and reduce disparities in AD risk.