Many people assume reaching age 90 without dementia signifies they’ve escaped the condition. New research indicates that is not necessarily true.
Researchers from the University of California, Davis Health and Kaiser Permanente tracked over 800 adults aged 90 and older as part of the ongoing LifeAfter90 study. They discovered that dementia risk persists well into advanced age, differing by sex, race, ethnicity, and genetics. Published in The Lancet Healthy Longevity, the findings are among the first to examine dementia risk in a diverse group of those over 90 without signs at enrollment.
Rachel Whitmer, a UC Davis Health professor of public health sciences and neurology and senior author of the study, stated, “We know from other studies on those aged 65 and older that there are differences in dementia rates, and women tend to have higher risk. No one knew if that was true after 90. We need to understand who is most affected by dementia after 90 and how the main Alzheimer’s risk gene, APOE, factors in.”
What the New Research Shows
Participants, Kaiser Permanente members, underwent assessments every six months for cognitive health changes. The long-term enrollment in the health system allowed researchers to examine historical records, some dating back to the 1960s.
The study’s results showed:
- Women remained more vulnerable to dementia than men even after age 90. Women had roughly double the risk compared to men.
- Racial and ethnic disparities persisted. Black participants had a 75 percent greater risk of dementia than Asian participants. Overall, Black and Hispanic participants had significantly higher dementia rates than White and Asian participants.
Hilary Colbeth, a UC Davis postdoctoral scholar in public health sciences and first author of the study, commented, “It is striking that racial and ethnic disparities in dementia risk in younger adults continue into the tenth decade of life. Specifically, Black and Hispanic participants had higher incidence rates than White and Asian participants.”
Researchers Also Looked at APOE
Researchers examined APOE, a gene linked to Alzheimer’s disease risk. One version, APOE2, is protective, while APOE4 is associated with increased risk. The study found APOE2 reduces dementia risk by about 60 percent even after age 90. The picture was more nuanced for APOE4. Across the population, APOE4 did not significantly increase incidence. However, analyzing specific groups separately showed elevated risk among men and nearly doubled risk among Black participants.
Colbeth stated, “We saw evidence that APOE4 impacts males and females differently after age 90. This has prompted us to look more closely at how APOE genotypes impact mortality among those with and without dementia after 90.”
An interesting finding emerged: some participants were cognitively healthy despite risk factors like hypertension or high cholesterol earlier in life. Others remained dementia-free despite carrying APOE4, prompting interest in what protected these individuals.
What the Findings Reveal
Lisa George, founder of Talk Tribeca Psychiatry in New York City and a dual board-certified NP in Psychiatry and Family Health not involved in the research, noted the findings challenge common misconceptions about aging.
“People think if someone makes it to 90 without dementia, they’re in the clear, but unfortunately, they aren’t,” George told Newsweek. “Age is still the biggest risk factor for dementia. Reaching your 90s with ‘intact cognition’ is encouraging but doesn’t mean dementia can’t develop later.”
George noted dementia becomes increasingly complex among the oldest old. Multiple processes can affect the brain simultaneously, including Alzheimer’s-related changes, vascular disease, and age-related brain changes.
“Dementia in the ‘oldest old’ is fascinating because two people can have similar brain changes and one develops dementia while the other remains sharp,” George said. “That’s the question I’d love researchers to answer. What protects the second person’s brain?”
She added memory concerns in very old adults should not automatically signal dementia. “From a psychiatric perspective, it’s important to remember not every memory complaint in a 90-year-old is dementia,” George said. “Depression, anxiety, poor sleep, medication side effects can mimic dementia.”
The study’s authors suggest these findings could help clinicians better recognize which groups remain at risk even in very old age.
As Whitmer noted, “Doctors need to know some groups are at higher or lower risk. We can’t assume someone from a high-risk group who reaches 90 without dementia is in the clear. We need to talk about risk reduction for everyone.”
What’s Next for Dementia Research?
The findings contribute to growing evidence that dementia risk doesn’t plateau after 90. This raises new questions about how aging, genetics, and lifelong health disparities influence cognitive decline in the oldest old. The study highlights the need for more research focused on people over 90, one of the fastest-growing age groups worldwide.
Broadly, Alzheimer’s research is moving towards earlier detection and prevention. Emerging blood-based biomarker tests measuring proteins linked to Alzheimer’s show promise in identifying risk years before symptoms appear. These might help researchers involve high-risk individuals in prevention trials.
Answers from studies like LifeAfter90 could 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). DOI: 10.1016/j.lanhl.2026.100882