The association between black individuals and processing speeds may explain the black-white disparities in dementia risk at older age.
Michelle R. Caunca, PhD
Data from the prospective cohort Coronary Artery Risk Development in Young Adults (CARDIA) study revealed that exposure to residential segregation throughout young adulthood was associated with worse processing speed among black individuals as early as midlife.
Analysis containing cognition data on 1568 black participants demonstrated that greater cumulative exposure to segregated neighborhoods was associated with a worse Digit Symbol Substitution Test (DSST) z score (for high segregation, β = −0.37 [95% CI, −0.61 to −0.13]; for medium segregation, β = −0.25 [95% CI, −0.51 to 0.0002]) relative to exposure to low segregation.
In comparison, the coefficient for baseline age was ­—0.07 (95% CI, –0.08 to –0.06), such that 1 extra year of age was associated with a 0.07-point decrease in DSST z score. Associations with Stroop Color Test and Rey Auditory Verbal Learning Test (RAVLT) performance did not reach statistical significance.
“The estimate for the association of high racial residential segregation with DSST was more than 5-fold that of the association of age with DSST,” Michelle R. Caunca, PhD, study author, medical student, Miller School of Medicine, University of Miami, and colleagues, concluded. The study was completed with the goal of examining the association between cumulative exposure to residential segregation during 25 years of young adulthood among black individuals and cognitive performance in midlife.
Originally, 5115 black and white participants, aged 18 to 30 years, were recruited from 4 field centers between February 1985 and May 2011, and included in CARDIA. In 2010, 3671 (71.8%) had survived and attended examination in year 25 of the study. Completion of cognitive assessments was achieved by 3008 (81.9%) of the patients. Data was analyzed from April 16 to July 20, 2019, with researchers using marginal structural models containing inverse probability weighting to account for time-varying confounding and differential censoring.
Researchers used the widely accepted Getis-Ord Local G statistic as a neighborhood-level residential segregation measure. Additionally, Cauna and colleagues created the exposure of interest, a measure of cumulative exposure to racial residential segregation that calculates the mean G statistic (Gi*) for each person across the follow-up period. Patients of CARDIA had mean cumulative exposure to segregation calculated at 6 follow-up visits from baseline, as well as Year 25 examination. Segregation levels were divided into high (Gi* > 1.96), medium (Gi*, 0—1.96), and low (Gi* < 0). At Year 25 examination, patients were evaluated on DSST, Stroop color test (reverse coded), and RAVLT. Z scores were calculated for all cognitive tests to facilitate comparison of estimates.
Mean baseline age across segregation categories was 25 years (standard deviation [SD], 4); 936 were women (59.7%) and 632 (40.3%) were men. Systolic blood pressure, body mass index, number of depressive symptoms, and alcohol consumption were similar across segregation categories.
“Racial residential segregation has been called a fundamental cause of black-white health disparities because it influences the distribution of resources and opportunities that can protect health and/or increase risk of disease,” Caunca and authors concluded. “Consistent with this theory, there are many pathways through which segregation could influence cognitive performance.”
Caunca MR, Odden MC, Glymour MM, et al. Association of racial residential segregation throughout young adulthood and cognitive performance in middle-aged participants in the CARDIA study. JAMA Neurol. Published online May 4, 2020. doi: 10.1001/jamaneurol.2020.0860.