A large community-based study reveals that more than 4 in 10 adults will develop dementia after age 55, with substantially higher lifetime risks found among women, Black adults, and those carrying the APOE ε4 gene variant.
The research, published in Nature Medicine, also projects the annual number of new dementia cases in the U.S. will roughly double to approximately 1 million by 2060.
The study, which followed 15,043 participants over three decades, found that women face a 48% lifetime risk of developing dementia compared with 35% for men. Black adults showed a 44% lifetime risk versus 41% for White adults. Those carrying 2 copies of the APOE ε4 gene variant faced the highest risk at 59%.
"The lifetime risk of dementia is a critical public health measure that can raise awareness, enhance engagement in prevention, and inform policymaking," the researchers wrote.
The median age of dementia diagnosis was 81 years, with notable disparities across populations. Black adults received diagnoses approximately 3 years earlier than White adults (median age 79 vs 82 years). Similarly, carriers of two APOE ε4 alleles were diagnosed about 3 years earlier than non-carriers (median age 79 vs 82 years).
The study found dementia incidence remained relatively low between ages 55-75 (3.9%) but increased substantially after age 75. Race-based differences in lifetime risk emerged around age 75, while sex-based differences became apparent around age 85.
The researchers attribute women's higher lifetime risk primarily to greater longevity rather than inherent susceptibility. The study found men experienced nearly double the rate of death without dementia compared to women, meaning fewer men survived to ages when dementia risk increased significantly.
For APOE ε4 carriers, the impact varied by race and sex. The presence of 2 APOE ε4 alleles increased lifetime dementia risk by 29 percentage points in White men and 19 percentage points in White women compared with non-carriers. However, among Black men, carrying 2 APOE ε4 alleles only increased risk by 5 percentage points.
The researchers project that approximately 514,000 new dementia cases will occur in 2020, rising to roughly 1 million annual cases by 2060. This increase appears particularly pronounced among Black adults, who are projected to see a tripling in new cases compared with a doubling among White adults.
The study used data from the Atherosclerosis Risk in Communities (ARIC) study, tracking participants from 1987 to 2020 across four US communities. Dementia cases were identified through cognitive testing at study visits, phone interviews, and review of medical and death records.
The researchers note that their lifetime risk estimates exceed those from previous studies, which typically reported 11-14% risk for men and 19-23% for women. They attribute this difference to their study's more comprehensive dementia surveillance methods and greater demographic diversity.
"Our results suggest that the current lifetime risk of dementia may be substantially higher than previously thought, emphasizing the importance of prevention throughout the life course," the researchers concluded, advocating for "policies that enhance prevention and healthy aging" with particular attention to health equity.
The research was supported by multiple institutes within the National Institutes of Health. Conflict of interest disclosures can be found in the study.