1. High exposure to racial residential segregation among African Americans resulted in worse mid-life processing speed performance compared to those with medium and low exposure, though set-shifting and memory changes were not significantly different across groups.
Evidence Rating Level: 2 (Good)
Residential segregation is a social determinant of health, found to be associated with poor health outcomes among African American individuals. The degree to which this segregation impacts cognitive performance in mid-life has been largely unexplored. The Coronary Artery Risk Development in Young Adults (CARDIA) study is a prospective cohort study which recruited 5,115 African American and Caucasian adults between the ages of 18 and 30 years across four medical centers across the U.S. Data was acquired from February 1985 to May 2011. This study was limited to those who self-reported as African American and excluded those who did not undergo cognitive testing, resulting in a total of 1,568 participants for analysis (M [SD] age = 25  years, 59.7% female). The Getis and Ord local Gi* statistic was used to measure neighborhood-level residential segregation, a method that is empirically-supported by measuring the relative racial composition of a given neighborhood compared to the larger metropolitan region. Proportions of African Americans in these neighborhood and metropolitan areas were obtained from the census, and spatial weight of individual racial tracts were compared to nearby tracts. The Gi* produces a z score representing the number of SDs that an individual’s neighborhood racial composition is from the surrounding area. Gi* was grouped into high (>1.96), medium (0-1.96), and low (<0). Individuals in high-segregation areas had lower education than medium- and low-segregation groups (difference 1 year). The high-segregation group was also more likely to be married and be current smokers. Lastly, this group exhibited decreased median total physical activity compared to medium- and low-segregation groups. Body mass index, number of depressive symptoms, alcohol consumption, and systolic blood pressure were similar across segregation groups. Cumulative racial residential segregation exposure was associated with decreased Digit Symbol Substitution Test (DSST; also known as Coding) performance (z scores) in a dose-dependent manner (high segregation β = -0.37 [95% CI -0.61 to -0.13]; medium segregation β = -0.25 [95% CI -0.51 to 0.0002]) compared to low segregation exposure. The baseline age coefficient (-0.07, 95% CI -0.08 to -0.06) suggested that a 0.07-point decrease in DSST z score would occur for every one year of aging. Tests of set-shifting and memory did not yield statistically significant differences across segregation groups; the DSST is a measure of processing speed that includes a motor component. Overall, this study suggests a negative, duration-dependent effect of racial residential segregation on processing speed in mid-life among African Americans. There are also notable differences between the groups in social determinants of health, such that this study highlights future areas of research.
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