Our fourth presenter, Dr. Jennifer Manly, is Associate Professor of Neuropsychology in Neurology at the Gertrude H. Sergievsky Center and the Taub Institute for Research in Aging and Alzheimer’s Disease at Columbia University. Her presentation, Lifecourse Social Conditions and Racial and Ethnic Patterns of Cognitive Aging, was a fitting culmination of the special session, as it brought together many of the themes that others on the panel had discussed.
Evidence for disparities in cognitive aging and Alzheimer’s disease
Dr. Manly began by summarizing the evidence for disparities in cognitive aging and Alzheimer’s disease (AD). According to multiple studies, the incidence and prevalence of cognitive impairment (which includes mild cognitive impairment as well as various forms of dementia, Alzheimer’s disease, and related dementias) is higher among African Americans and Hispanics than among non-Hispanic whites. More detailed information is available in this review.
Methodological challenges to AD disparities research
While the evidence of disparities appears strong, it must be interpreted in the context of the methodological challenges associated with this area of research. These include selection bias, survival bias, and complex causal pathways linking race/ethnicity, cognitive aging, and AD. Lack of data on, and adjustment for, important factors in AD incidence are also common.
Some researchers have proposed that African ancestry is associated with higher risk for cognitive decline in aging and dementia. As shown in a recent study by Marden, Walter, Kaufman, & Glymour, African ancestry is correlated with social factors, including:
- Less education
- Fewer years of parental schooling
- Higher likelihood of no inheritance
- Lower income (by an average of about $1,400/year)
- Less wealth (by an average of about $12,000)
Differences in school quality may also obscure or alter that relationship. Educational attainment, whether measured in years or credentials, ignores tremendous variability in quality of schooling. Most African American seniors alive today experienced segregated school systems with different school year lengths, student-teacher ratios, and curricula. These differences led to inequalities in educational experience that are not reflected in years of schooling, yet few researchers account for this in their estimates.
Racial/ethnic disparities in AD are attenuated in analyses that adjust for key confounders
Dr. Manly finished by sharing data from the Washington/Hamilton Heights-Inwood Columbia Aging Project (WHICAP), an ongoing, community-based study of aging and dementia. In that study, models adjusted only for age/sex result in an AD incidence hazard ratio (HR) of 2.3 for African Americans and 3.1 for Hispanics. Models further adjusting for genetic markers, comorbidities, health behaviors, and years of education still found significantly higher HRs for both African Americans and Hispanics relative to non-Hispanic whites. However, after further adjusting for occupation, income, and reading level, there were no significant differences between ethnoracial groups (see presentation slides for details).
Dr. Manly concluded her presentation, and we will conclude this blog post, with the following important points:
- Indicators of school quality explain racial disparities in cognitive function cross-sectionally and longitudinally, and also explain AD incidence trends.
- Sociocultural factors correlate with African ancestry and may confound the relationships between African ancestry and AD risk.
- Intervening on psychosocial factors may narrow disparities in cognitive decline and improve responses to interventions.