Black People Have Faster Cognitive Decline Than Whites Irrespective of Socioeconomic Status, Vascular Risk and Brain Pathology

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Much of the current research into Alzheimer's disease is aimed at secondary prevention—detecting the disease early and preventing it from worsening. Relevant to this effort are previous findings that Black Americans are about twice as likely as white Americans to develop dementia, but rates of cognitive decline are similar in the two groups once baseline disparities in socioeconomic, psychosocial and vascular risk factors are considered.

Rebecca E. Amariglio, PhD, clinical neuropsychologist at Mass General Brigham, and Reisa A. Sperling, MD, who co-leads the Harvard Aging Brain Study at Massachusetts General Hospital, and colleagues recently dug deeper into race-based differences. They compared Black and white participants who were cognitively normal at baseline, and they controlled for brain pathology: white matter hyperintensities (WMH) on MRI, which reflect subclinical cerebrovascular disease, and amyloid-β (Aβ) plaque burden on positron emission tomography, a pathologic hallmark of Alzheimer's disease.

As the team reports in the Journal of Alzheimer's Disease, this analysis showed that the rate of cognitive decline was worse in Black participants than in white participants, despite adjustment for brain pathology and multiple other covariates.

Study Design

The researchers used data on 48 Black and 249 white participants in the Harvard Aging Brain Study, an ongoing observational study. The average age at baseline was 73 (range, 50–89).

The participants underwent brain MRI and PET, and at baseline and annually thereafter, they completed the Preclinical Alzheimer's Cognitive Composite–version 5 (PACC5). That instrument is designed to detect subtle cognitive changes characteristic of preclinical Alzheimer's disease.

Baseline Results

Black participants demonstrated more impairment on the PACC5 than white participants did (β = −0.28; P = 0.002) after adjustment for age, sex, education level and reading ability. The discrepancy persisted (β = −0.24; P = 0.01) even after the researchers further adjusted for Framingham Heart Study (FHS) cardiovascular risk score, WMH and Aβ plaque burden.

Cognitive Decline

The performance of Black participants on the PACC5 declined at a rate 0.05 standard deviations per year greater than that of white participants of the same age and sex. Consideration of baseline PACC5 score did not significantly alter this finding.

Cognitive Decline—Adjusted Results

• After adjustment for educational factors, there was a faster rate of cognitive decline over time for Black participants than for whites (β = −0.06; t = −2.26)
• After adjustment for FHS score, WMH and Aβ burden, the difference in cognitive decline by race remained (β = −0.06; t = −2.25)
• Performance on the PACC5 declined faster in Black participants with elevated Aβ than in white participants with elevated Aβ (β = −0.27; t = −1.99)

Continued Scrutiny Needed

Further work is sorely needed to identify the mechanisms that underlie the differences between Black and white Americans in the rate of cognitive decline. Otherwise, Black patients with Alzheimer's disease may not benefit as much as white patients from any advances in secondary prevention.

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