Living to 90 with your memory intact does not put you beyond the reach of dementia, according to new findings from the LifeAfter90 study published in The Lancet Healthy Longevity. Researchers at UC Davis Health and Kaiser Permanente report that among adults in their 90s, dementia risk still differs meaningfully by sex, race, ethnicity and genetics - patterns that had gone largely unmeasured in this age group.
Most of what is known about who develops dementia comes from studies of people 65 and older. In those populations, women tend to carry higher risk. Whether that pattern holds once people pass 90 was an open question. "Nobody knew if that was true after 90," said Rachel Whitmer, professor of public health sciences and neurology at UC Davis Health, chief of epidemiology and the study's senior author, who added that researchers also need to understand how APOE, the main Alzheimer's risk gene, factors in at these ages.
The LifeAfter90 team has followed a large group of adults in their 90s since 2018, which is what makes the analysis possible. The oldest old have historically been thin on the ground in dementia research, and assumptions drawn from younger seniors have simply been extended upward without much evidence behind them.
The practical stakes are growing quickly. By 2100, an estimated 230 million people worldwide could be 90 or older. Knowing which groups in that population face the highest dementia risk - and how genetic risk behaves at very advanced ages - shapes everything from how families plan for care to how clinicians interpret a 92-year-old's cognitive testing.