Researchers at UC Davis Health and Kaiser Permanente have published findings from LifeAfter90, a study that has followed a large group of people aged 90 and older since 2018. Writing in The Lancet Healthy Longevity, the team describes differences in dementia risk between men and women and across racial and ethnic groups, along with how brains at this advanced age respond to genetic risk factors, including APOE, the main Alzheimer's risk gene.
That may sound like territory already well covered, but it is not. Most of what is known about dementia risk comes from studies of people 65 and older, and those results have generally been assumed to carry forward into the tenth decade of life without much direct evidence. As Rachel Whitmer, professor of public health sciences and neurology at UC Davis Health and senior author on the study, put it, women are known to have a higher risk in younger cohorts, but no one knew whether that pattern held after 90.
The design is what makes the data unusual. LifeAfter90 participants are Kaiser Permanente members who joined the study before showing any signs of dementia, and researchers have examined them every six months since to track cognitive changes as they happen rather than reconstructing them after the fact. That kind of close, repeated follow-up in the oldest old is rare.
The practical stakes are growing quickly. By 2100, an estimated 230 million people worldwide could be 90 or older, and clinicians and policymakers currently have thin evidence to guide care and planning for that group. Knowing who is most affected by dementia after 90, and how established genetic risk factors behave at that age, is a starting point for tailoring support to a population that until now has largely been studied by extrapolation.