In the United States, Racial Disparities in Dementia Risk Persist

In the U.S., African Americans are more likely to get dementia than are whites. It is unclear why, although it could have something to do with a higher burden of cardiovascular disease, which boosts dementia risk. Societal improvements in heart health in recent decades have nudged down overall dementia incidence; has this helped close the racial gap? No, according to researchers led by Melinda Power at George Washington University in D.C. In the November 30 JAMA Neurology, they report that, in a longitudinal cohort study, blacks continued to have a higher risk of dementia than whites over a period of 16 years, even while overall incidence fell slightly in both groups. “Additional effort to identify and mitigate factors contributing to these disparities is warranted,” the authors wrote.

  • Dementia incidence has fallen in the last three decades.
  • Even so, the racial gap between black and white people persists.
  • This may relate to cardiovascular health, education, or other factors.

In an accompanying editorial, Carl V. Hill of the Alzheimer’s Association in Chicago suggested that socioeconomic factors and stress due to racial inequalities might interact to cause poorer health outcomes in African Americans. Research to date has focused more on individual risk factors than societal ones, he noted. “Researchers must continue to push the boundaries of the field and account for the lived experiences that increase risk for black Americans,” he wrote.

Several studies have found up to twice the incidence of Alzheimer’s disease among blacks as whites (Tang et al., 2001; Weuve et al., 2018; Oct 2018 news). Few studies, however, have addressed whether this relative risk has changed over the last three decades as overall dementia incidence has fallen (May 2013 news; Feb 2016 news; Nov 2016 news). 

To examine this, Power and colleagues analyzed data from the Health and Retirement Study. It follows older U.S. adults in their communities with assessments every two years. The authors used data from nine such assessments, 2000 through 2016. Approximately 6,000 white and 1,000 black participants were enrolled at each of these time points. Demographically, the two groups were quite different. The white population’s average age was 79; 58 percent of them were women. The black population was slightly younger, at an average age of 78, and more female, with 63 percent women. One-quarter of whites had some college education, while 19 percent did not complete high school. Blacks had less education, with 12 percent attending college and 48 percent not finishing high school. Finally, 64 percent of whites had hypertension, and 20 percent had diabetes. This chronic disease burden was higher for blacks, with 79 percent having hypertension, and 33 percent diabetes.

The researchers determined dementia status every two years based on cognitive and functional scores, using algorithms shown to perform similarly in blacks and whites (Gianattasio et al., 2019). Overall, about 20 percent of participants had dementia, with the prevalence falling by about 10 percent between 2000 and 2016. Despite this, the racial disparity remained stable. At every timepoint, blacks had 1.5 to 1.9 times the dementia prevalence as whites. Similarly, cognitively healthy blacks were 1.4 to 1.8 times more likely to develop dementia over the next four years than were whites.

Notably, during these 16 years, the average education level climbed for both black and white participants, though it increased more dramatically for the former. Alas, the prevalence of hypertension rose equally for both, while diabetes rose more in blacks than whites. Diabetes and hypertension are both linked to body weight, which is also a risk factor for dementia, but BMI was not reported for this study (Sep 2015 news). 

“What appears to have remained stable is the effect of what the authors call structural racism,” Walter Rocca at the Mayo Clinic in Rochester, Minnesota, wrote to Alzforum (full comment below). Carol Brayne at the University of Cambridge, U.K., agreed. “It would be good to place the findings … in the context of the changing social environments of the different populations included, and how policy changes have been the same and different across groups. This might help to disentangle what the major drivers for our populations are,” she wrote to Alzforum (full comment below).—Madolyn Bowman Rogers

Comments

  1. This is an important new piece of the puzzle about time trends in the risk of dementia. The novel observation is that the racial disparities in prevalence and incidence have not changed over 16 years, between 2000 and 2016 in the United States. The implication is that the risk or protective factors that did underlie the difference between black and white participants in 2000 continue to underlie the difference in 2016.

    Some known risk or protective factors for dementia have changed over time differently in the two groups. For example, education has improved in both racial groups, but more among black participants. Hypertension and diabetes have increased in both groups, but more among black participants. 

    What appears to have remained stable is the effect of what the authors call structural racism. They describe structural racism as the result of life-long and complex interactions of factors such as educational attainment and quality, work experiences, income, family structure, burden of vascular risk factors, and stress caused by the personal experience of racism and discrimination. Structural racism may affect brain health at any stage of life through material, behavioral, and biological mechanisms.

    Understanding the causes of the differences between blacks and whites is essential to reduce or eliminate such disparities.

    View all comments by Walter A. Rocca

  2. This is an important analysis of the HRS data, providing as close a representation of the U.S. population as is possible, with sufficient diversity to make comparisons across time. The finding of stable relative relationships and decline in prevalence in diverse ethnicities is both bad and good. It suggests that whole societal influences are influencing shape of change, but that the relative ones are associated with others that have not changed.

    It would be good to place the findings, and the authors start to do this, in the context of the changing social environments of the different populations included, and how policy changes have been the same and different across groups. This might help to disentangle what the major drivers for our populations are.

    The paper’s messages that reduction is seen across time in all populations but that inequalities in this lifecourse outcome disorder for the brain are still very clear are rallying calls to policy makers to build on the success and address the enduring and unacceptable differences in our societies.

    View all comments by Carol Brayne

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References

News Citations

  1. Do African-Americans Have More, or Different, Alzheimer’s Disease? Too Little Data to Tell
  2. Dementia Incidence Said to Drop as Public Health Improves
  3. Falling Dementia Rates in U.S. and Europe Sharpen Focus on Lifestyle
  4. U.S. Dementia Rates Fall
  5. Extra Weight in Midlife Hastens Onset of Alzheimer’s Disease

Paper Citations

  1. Tang MX, Cross P, Andrews H, Jacobs DM, Small S, Bell K, Merchant C, Lantigua R, Costa R, Stern Y, Mayeux R. Incidence of AD in African-Americans, Caribbean Hispanics, and Caucasians in northern Manhattan. Neurology. 2001 Jan 9;56(1):49-56. PubMed.
  2. Weuve J, Barnes LL, Mendes de Leon CF, Rajan KB, Beck T, Aggarwal NT, Hebert LE, Bennett DA, Wilson RS, Evans DA. Cognitive Aging in Black and White Americans: Cognition, Cognitive Decline, and Incidence of Alzheimer Disease Dementia. Epidemiology. 2018 Jan;29(1):151-159. PubMed.
  3. Gianattasio KZ, Wu Q, Glymour MM, Power MC. Comparison of Methods for Algorithmic Classification of Dementia Status in the Health and Retirement Study. Epidemiology. 2019 Mar;30(2):291-302. PubMed.

Further Reading

Primary Papers

  1. Power MC, Bennett EE, Turner RW, Dowling NM, Ciarleglio A, Glymour MM, Gianattasio KZ. Trends in Relative Incidence and Prevalence of Dementia Across Non-Hispanic Black and White Individuals in the United States, 2000-2016. JAMA Neurol. 2021 Mar 1;78(3):275-284. PubMed.

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