Racially Segregated Neighborhoods Bad for the Brain?

Megan Brooks

May 11, 2020

Living in racially segregated neighborhoods in young adulthood is associated with poor cognitive function in midlife, new research shows.

Investigators found that black individuals who lived in highly segregated neighborhoods throughout young adulthood had worse processing speed than their counterparts living in less segregated areas by the time they reached middle-age — an effect that was fivefold greater than the impact of aging on cognition.

"These findings may explain black–white disparities in dementia risk at older age," study investigator Adina Zeki Al Hazzouri, PhD, a researcher in the Department of Epidemiology, Mailman School of Public Health at Columbia University in New York City, told Medscape Medical News.

The study was published online May 4 in JAMA Neurology.

“Disconcerting” Findings

Neighborhood-level residential segregation has previously been tied to poor health outcomes among black individuals, but the literature examining the association of racial residential segregation with cognitive function is limited.

Zeki Al Hazzouri and colleagues evaluated the link between cumulative exposure to residential segregation during 25 years of young adulthood and cognitive performance in middle age in 1568 black adults participating in the Coronary Artery Risk Development in Young Adults (CARDIA) study. The mean age of participants at baseline was 25 years and 60% were women.

Racial residential segregation was categorized as high, medium, or low, with 1286, 188 and 94 participants in each group, respectively. 

Cognitive function was measured at year 25 of the study, using the Digit Symbol Substitution Test (DSST), Stroop color test (reverse coded), and Rey Auditory Verbal Learning Test.

Greater cumulative exposure to segregated neighborhoods was associated with a worse DSST z score relative to exposure to low segregation, whereas the association with the other two performance tests did not reach statistical significance.

Table. Association Between Cumulative Exposure to Racial Segregation Throughout Young Adulthood and Midlife Cognitive Function

Racial residential segregation DSST β (95% CI)
High –0.37 (–0.61 to –0.13)
Medium –0.25 (–0.51 to 0.0002)
Low  1 [reference]

DSST – Digit Symbol Substitution Test

 

"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," the investigators report.

They suggest interventions targeting "mediating pathways" of this association may help lower the risk of cognitive impairment in black residents living in highly segregated neighborhoods.

"More importantly," they note, policies that address segregation and the uneven distribution of resources "may be beneficial for reducing inequities in cognitive performance."

Consequences of an Unjust Society

Reached for comment, Harlan Krumholz, MD, from Yale University School of Medicine in New Haven, Connecticut, said this "disconcerting study documents some of the likely harms deriving from structural racism throughout our society."

"The segregation of segments of our population surely have so many critical economic harms, but this study reveals the possibility that there are direct health harms, as measured here by cognitive function," Krumholz told Medscape Medical News.

"We do not need a reason to make society more just, but studies like this help us face up to the consequences of our unjust society and should stimulate us to work harder to address these circumstances," said Krumholz.

Support for the study was provided by the National Institutes of Health. Zeki Al Hazzouri and Krumholz have disclosed no financial relationships relevant to this study.

JAMA Neurology. Published online May 4, 2020. Abstract

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