Which populations are most vulnerable to Alzheimer’s disease and why?

Multiple environmental, sociocultural, behavioral, and biological factors determine vulnerability to AD

As average life expectancy increases, the prevalence of dementia is expected to increase, and by 2050, most cases will be in developing countries, the audience was informed.

Meanwhile, the incidence of dementia is declining in high-income countries, with the incidence of dementia in the Framingham Heart Study declining over the past three decades.¹ The reasons for the decline are not clear, but multiple factors — environmental, sociocultural, behavioral, and biological — determine the incidence and prevalence of AD.²

Populations most vulnerable to dementia

Birth in a high-stroke mortality state is associated with a 28% higher risk of dementia

A large population-based sample with equal access to healthcare was followed for 14 years and revealed dementia incidence to be:

• highest among African Americans and American Indian/Alaska Natives
• lowest among Asian Americans
• intermediate among Latinos, Pacific Islanders, and Whites³

These patterns of racial/ethnic disparities in dementia have also been shown in individuals over 90 years of age.⁴

Explanations for the differences between the racial/ethnic groups, such as education (eg, it has been suggested that the higher risk of AD among African Americans may result from a lower level of cognitive test performance related to disparities in educational attainment),⁵ genetics, and vascular comorbidities were not demonstrated, and lifecourse risk factors are being investigated.³

• In terms of other comorbidities, older Mexican Americans with diabetes at baseline experience faster rates of cognitive decline than those without diabetes, while new-onset diabetes is not associated with rate of cognitive decline.⁶
• Birth in a high-stroke mortality state in the United States is associated with a 28% higher risk of dementia — birth in a high-stroke mortality state is 9.6 times more common for African Americans than for non-African Americans.⁷

Strategies to reflect the diversity of Alzheimer’s disease in clinical studies

Understanding the causes of health disparities is a first step to eliminating them

It is estimated that reducing dementia rates in all racial/ethnic groups to the rates observed among Asian Americans would prevent over 190,000 cases of dementia each year in the United States.³ 

Health disparities therefore need to be investigated in a rigorous and thoughtful manner by:

• asking the right questions
• using the correct methods
• contextualizing the research in terms of education, bilingualism, and occupation; and using contextualized research instruments with cultural relevance
• harmonization of analytic approaches across studies and subsequent pooling of data

Need to balance the breadth and depth of studies

It was also emphasized that there needs to be a balance between:

• the breadth of the study — the size of the study population and the extent to which it adequately reflects known risk factors in terms of its racial and ethnic, educational, and geographic diversity; and
• the depth of the study — in terms of which tissue, brain, plasma, and imaging biomarkers are used

Furthermore, researchers were advised to ask themselves the following three questions to acquire a meaningful understanding of the sources of racial health disparities:⁸

1. Are there substantive between-group differences in outcome prevalence?
2. Are there substantive between-group differences in exposure prevalence?
3. Are there substantive between-group differences in the relationship between the exposure and outcome?