A recent study published in The Lancet Healthy Longevity advances understanding of dementia risk among people aged 90 and older, according to findings released on Aug. 4 by researchers at UC Davis Health and Kaiser Permanente. The LifeAfter90 study tracked a large group of individuals over the age of 90 since 2018 to investigate how advanced age affects cognitive health, with a focus on differences between genders and racial or ethnic groups.
Rachel Whitmer, UC Davis Health professor of public health sciences and neurology, chief of epidemiology, and senior author on the study, said, "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. We need to understand who is most affected by dementia after 90 and how the main Alzheimer's risk gene (APOE) factors in."
The LifeAfter90 participants are long-term Kaiser Permanente members who enrolled before showing signs of dementia. Researchers followed these patients every six months to assess their cognitive health. Medical records from over 800 participants with a median age of 92 were examined for this research—the first effort to investigate dementia after age 90 in such a highly diverse cohort.
Findings showed that women aged 90 or older have twice the risk for developing dementia compared to men. Racial and ethnic disparities similar to those seen in younger populations also persisted; Black participants had a 75% greater risk than Asian participants. Hilary Colbeth, UC Davis postdoctoral scholar in public health sciences and first author on the paper, said, "It is striking that the racial and ethnic disparities in dementia risk observed in younger adults continue into the tenth decade of life. Specifically, Black and Hispanic participants had significantly higher dementia incidence rates than white and Asian participants."
The study also analyzed genetic factors related to Alzheimer's disease. The APOE2 gene variant continued its protective effect past age 90 by reducing Alzheimer's risk by about sixty percent for carriers; meanwhile, APOE4 increased overall risk primarily among men as well as doubling it for Black participants specifically.
Researchers caution that more questions remain regarding why some individuals with known risks—such as hypertension or high cholesterol—remained cognitively healthy into their nineties while others did not. Whitmer concluded, "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 ninety without dementia and they're in the clear."
