Researchers at Vanderbilt Health have discovered something that challenges a fundamental assumption about dementia: Black and Hispanic people with cognitive impairment are significantly less likely to show Alzheimer's pathology on brain scans, even though they develop dementia at far higher rates than other groups. The finding, based on 5,757 Medicare recipients across the country, suggests that the stark racial and ethnic disparities in dementia may stem not from a single disease, but from multiple, overlapping causes that have been largely invisible to modern medicine.
This contradiction matters deeply. Dementia already strikes Black Americans 54% more often than white Americans and Hispanic Americans 92% more often, according to a 2022 study of 1.9 million people. Yet the new research, published in Alzheimer's & Dementia: The Journal of the Alzheimer's Association, reveals that among people with mild cognitive impairment or dementia, Black participants showed 28% lower odds of amyloid positivity on positron emission tomography (PET) scans, while Hispanic participants showed 22% lower odds. Amyloid plaques are considered the hallmark of Alzheimer's disease, which accounts for 60–80% of dementia cases overall.
"These results suggest that the yawning ethnoracial differences in dementia may be driven in part by group differences in underlying causes of dementia symptoms," said Dr. Consuelo Wilkins, the Mildred Thornton Stahlman Professor in Rural Health at Vanderbilt, who led the study. The research team, which included 18 co-authors from 11 institutions, deliberately gathered one of the largest and most diverse cohorts ever studied with PET brain imaging: 22% of participants were Black, 20% were Hispanic, and 58% were from other racial and ethnic groups.
The implications are troubling. In current clinical practice, normal PET results often mean reduced access to Alzheimer's treatments and exclusion from clinical trials. Black and Hispanic participants in this study were more than twice as likely to be enrolled in Medicare Advantage plans—a finding the researchers tie to barriers in accessing specialized care—and were more likely to present with full dementia rather than mild cognitive impairment. "Our results confirm that these disadvantages are apt to fall inordinately on Black and Hispanic people," said Dr. Corey Bolton, first author and assistant professor in Vanderbilt's Division of Geriatric Medicine.
Geography and economic circumstance also shaped the picture. Participants in distressed neighborhoods showed 40% higher odds of amyloid positivity than those in prosperous areas, suggesting that social determinants of health play a significant role in which type of dementia people develop. Comfortable neighborhoods showed 22% higher odds compared to prosperous areas.
The research offers no easy answers, only an urgent call to look beyond Alzheimer's. People who develop other forms of dementia—vascular dementia, Lewy body disease, frontotemporal dementia—may have no amyloid plaques at all. Dr. Wilkins put it plainly: "We need desperately to combat the scourge of Alzheimer's, but our results highlight that a fixation on Alzheimer's pathology, to the exclusion of other causes of dementia, could inadvertently worsen stark ethnoracial health differences." For Black and Hispanic Americans already burdened by disproportionate rates of cognitive decline, a narrower diagnostic lens could become another barrier to understanding and treatment.