Reaching 90 Without Dementia Doesn't Mean the Risk Is Gone, Study Finds

People who reach their 90s without dementia might seem to have escaped much of the risk of cognitive decline. But a new study finds that dementia risk still varies sharply within this age group, depending on sex, race, ethnicity and genetics. The findings come from the LifeAfter90 study, run by researchers at UC Davis Health and Kaiser Permanente, who have followed a large group of adults in their 90s since 2018, and are published in The Lancet Healthy Longevity. By 2100, roughly 230 million people aged 90 or older could be alive worldwide, making such data increasingly important.

"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," said Rachel Whitmer, UC Davis Health professor of public health sciences and neurology and the study's senior author. The new analysis included more than 800 Kaiser Permanente members, with a median age of 92. None showed signs of dementia when they enrolled. It is the first study of dementia after 90 conducted in a highly diverse group.

Women aged 90 and older had about twice the dementia risk of men. Black participants faced a 75% higher risk than Asian participants. "It is striking that the racial and ethnic disparities in dementia risk observed in younger adults continue into the tenth decade of life," said Hilary Colbeth, a UC Davis postdoctoral scholar and the study's first author, who noted that Black and Hispanic participants had significantly higher dementia rates than white and Asian participants.

The researchers also examined APOE, a gene strongly linked to Alzheimer's disease. Carrying the protective APOE2 variant was associated with a 60% lower risk of dementia even beyond age 90. The APOE4 variant, known to raise risk, did not substantially increase dementia rates across the study group as a whole, but it was associated with higher risk among men, and it nearly doubled dementia risk among Black participants who carried it.

The study also found a mystery still to be explained. Some participants had well-established risk factors, such as high blood pressure and high cholesterol, in their 60s and 70s, yet remained cognitively healthy decades later, and some who carried APOE4 still reached their 90s without dementia. "We can't just assume that someone from a high-risk group makes it to 90 without dementia and they're in the clear," Whitmer said. "We need to talk about risk reduction for everyone."