I should easily get to 90, and without dementia.
Scientists followed 800 adults over 90. One group had double dementia risk
Many people assume that reaching age 90 without dementia means they have escaped the condition; however, new research suggests that is not necessarily the case.
Researchers from the University of California, Davis Health and Kaiser Permanente tracked more than 800 adults aged 90 and older as part of the ongoing LifeAfter90 study and found that dementia risk continues well into advanced age, with notable differences by sex, race, ethnicity and genetics.
The findings, published in The Lancet Healthy Longevity, are among the first to examine dementia risk in a highly diverse group of people aged over 90 who did not have signs of dementia at enrollment.
“We know from other studies, done in people 65 and older, that there are differences in dementia rates, and women tend to have higher risk, but nobody knew if that was true after 90,” Rachel Whitmer, a UC Davis Health professor of public health sciences and neurology and senior author of the study, said. “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, who were Kaiser Permanente members, were assessed every six months so researchers could monitor changes in cognitive health. Because many had been enrolled in the health system for decades, investigators were also able to examine historical health records, in some cases dating back to the 1960s.
Moreover, women had roughly double the risk of developing dementia compared with men.
- Racial and ethnic disparities persisted as well. Black participants had a 75 percent greater risk of dementia than Asian participants. Overall, Black and Hispanic participants experienced significantly higher dementia incidence rates than White and Asian participants.
“It is striking that the racial and ethnic disparities in dementia risk observed in younger adults continue into the 10th decade of life,” said Hilary Colbeth, a UC Davis postdoctoral scholar in public health sciences and first author of the study. “Specifically, Black and Hispanic participants had significantly higher dementia incidence rates than white and Asian participants.”
Researchers Also Looked at APOE
The researchers also looked at APOE, a gene long associated with Alzheimer’s disease risk. One version of the gene, APOE2, is considered protective, while another, APOE4, is associated with increased Alzheimer’s risk.
The study found that APOE2 continued to provide protection even after age 90, reducing dementia risk by about 60 percent.
The picture was more complicated for APOE4. Across the study population as a whole, APOE4 did not substantially increase dementia incidence. However, when specific groups were analyzed separately, the variant was linked to elevated risk among men and nearly doubled dementia risk among Black participants.
“We saw evidence that APOE4 impacts males and females differently after age 90,” Colbeth said. “This has prompted us to look more closely at how APOE genotypes impact mortality among those with and without dementia after age 90.”
Researchers also noted an intriguing finding: some participants remained cognitively healthy despite having risk factors such as hypertension or high cholesterol earlier in life. Others remained dementia-free despite carrying APOE4. Understanding what protected these individuals is now a major area of interest.
What the Findings Reveal
For Lisa George, founder of Talk Tribeca Psychiatry in New York City and a dual board-certified NP in Psychiatry and Family Health who was not involved in the research, the findings challenge a common misconception 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, so reaching your 90s with what we call ‘intact cognition’ is encouraging but it doesn’t mean someone can’t develop dementia later on.”
George said dementia becomes increasingly complex in the “oldest old” because multiple processes can affect the brain simultaneously, including Alzheimer’s-related changes, vascular disease and age-related brain changes.
“That’s one of the reasons dementia in the ‘oldest old’ is so fascinating becuase two people can have very similar changes in their brains and one develops dementia while the other is still sharp as a tac,” she said. “That’s the question I’d love researchers to answer. What is protecting that second person’s brain?”
She added that memory concerns in very old adults should not automatically be assumed to signal dementia.
“From a psychiatric perspective, its so important to remember that not every memory complaint in a 90-year-old is dementia,” George said. “I’ve seen depression, anxiety, poor sleep, medication side effects all look like dementia.”
The study’s authors say the findings could help clinicians better recognize which groups remain at elevated risk even after reaching very old age. As Whitmer put it, “Doctors need to know that certain groups are at higher or lower risk.”
“We can’t just assume that someone from a high-risk group makes it to 90 without dementia and they’re in the clear,” she said. “We need to talk about risk reduction for everyone.”
What’s Next for Dementia Research?
The findings add to a growing body of evidence that dementia risk does not plateau after age 90, raising new questions about how aging, genetics and lifelong health disparities influence cognitive decline in the oldest-old.
The study also highlights the need for more research focused specifically on people over 90, one of the fastest-growing age groups worldwide.
More broadly, Alzheimer’s research is moving toward earlier detection and prevention. New blood-based biomarker tests that measure proteins linked to Alzheimer’s disease are showing promise in identifying risk years before symptoms appear and could help researchers enroll high-risk individuals in prevention trials.
Answers from studies like LifeAfter90 could help 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
Contact Newsweek editors on this story: Kara Dolman and Gray R. Thomas
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