Recent research challenges the belief that reaching age 90 without dementia means escaping the condition. The study by the University of California, Davis Health and Kaiser Permanente tracked over 800 adults aged 90 and above as part of the ongoing LifeAfter90 study. Researchers found that dementia risk persists into advanced age and varies by sex, race, ethnicity, and genetics. Published in The Lancet Healthy Longevity, this study is among the first to explore dementia risk in a diverse group of people over 90 without initial signs of the condition.

Research Findings

Participants, affiliated with Kaiser Permanente, underwent assessments every six months to monitor cognitive health changes. Many had long-term health records dating back to the 1960s, providing valuable historical data.

The study’s results revealed certain patterns:

• Women remained more susceptible to dementia than men, even after age 90. They had approximately double the risk of developing dementia compared to men.
• Racial and ethnic differences persisted. Black participants faced a 75% higher dementia risk than Asian participants. Overall, Black and Hispanic individuals experienced significantly higher dementia incidence rates than White and Asian groups.

According to Hilary Colbeth, a UC Davis postdoctoral scholar and the study’s first author, these racial and ethnic disparities in dementia risk observed in younger adults continue into later life.

Genetic Factors and APOE

Researchers also focused on APOE, a gene associated with Alzheimer’s disease risk. The APOE2 variant offers protection and continues to reduce dementia risk by about 60% beyond age 90. In contrast, the APOE4 variant did not significantly increase dementia incidence overall. However, it nearly doubled dementia risk among Black participants and impacted men more prominently than women after age 90.

These findings prompted further investigation into how APOE genotypes influence mortality among those with and without dementia beyond age 90. Some participants defied odds by remaining cognitively healthy despite having risk factors like hypertension or high cholesterol earlier in life, or carrying APOE4. Understanding what protected these individuals is now a major area of interest.

Implications of the Findings

Lisa George, founder of Talk Tribeca Psychiatry in New York City, noted that these findings challenge common misconceptions about aging. She emphasized that age remains the most significant dementia risk factor, and reaching one’s 90s with intact cognition does not preclude later development of dementia.

George highlighted that dementia in the “oldest old” is complex, as multiple processes can impact the brain. This complexity means that similar brain changes can result in different cognitive outcomes. Memory concerns in very old adults should not be immediately attributed to dementia, as other factors like depression, anxiety, poor sleep, or medication side effects can mimic its symptoms.

The study’s authors believe the findings can help clinicians better recognize high-risk groups, even among those reaching advanced age. Professionals must be aware of differences in dementia risk based on demographics and genetic factors.

Future Research Directions

The study extends evidence that dementia risk does not plateau after 90. It raises questions on how aging, genetics, and lifelong health disparities affect cognitive decline in this age group. The findings underline the need for more research specifically targeting individuals over 90, a rapidly growing demographic worldwide.

Alzheimer’s research is increasingly focused on earlier detection and prevention. Emerging blood-based biomarker tests measuring Alzheimer’s-related proteins show promise in identifying risk years before symptoms emerge. This could enable researchers to enroll high-risk individuals in prevention trials. Insights from studies like LifeAfter90 might guide future screening, treatment, and prevention strategies for an aging population.

Reference: Hilary L Colbeth et al, “Incidence of dementia after age 90 years and association with APOE genotype, race, and sex in the USA: the LifeAfter90 prospective cohort study,” The Lancet Healthy Longevity (2026).

For further information, contact Newsweek editors Kara Dolman and Gray R. Thomas.