Dementia Risk Remains Uneven Even After Age 90, Study Finds

Dementia risk does not simply disappear after age 90, according to findings from the LifeAfter90 prospective cohort study, which followed more than 800 adults who were free of dementia when they enrolled. The results, published in The Lancet Healthy Longevity, found that dementia incidence remained associated with sex, race, ethnicity and genetic factors.

The study included Kaiser Permanente members with a median age of 92. Researchers evaluated participants every six months, drawing on medical records that in some cases reached back to the 1960s. The analysis was conducted by researchers at UC Davis Health and Kaiser Permanente and was described as the first study of dementia after age 90 in a highly diverse cohort.

Women aged 90 and older had about twice the dementia risk of men. The researchers also found differences across racial and ethnic groups. Black participants had a 75% higher risk than Asian participants, while the study reported significantly higher dementia incidence among Black and Hispanic participants than among white and Asian participants.

Genetic differences remained relevant as well. The analysis examined variants of APOE, a gene associated with Alzheimer’s disease risk. Participants carrying APOE2, which the researchers described as protective, had a 60% lower risk of dementia. APOE4 showed a more complex pattern: across the full study population, it did not substantially increase dementia incidence, but it was associated with higher risk among men and approximately doubled risk among Black participants.

The findings do not establish that these factors directly caused dementia or prevented it. They show how dementia incidence differed across groups in this cohort of very old adults. The results also do not mean that genetic risk determines an individual’s outcome.

Some participants remained cognitively healthy despite having risk factors such as hypertension and high cholesterol during their 60s and 70s. Others carried APOE4 but reached their 90s without developing dementia. Researchers said they now want to investigate the biological or environmental characteristics that may have helped protect these individuals.

The study addresses a population that has received comparatively little research attention as lifespans increase. Its findings suggest that reaching 90 without dementia does not place everyone at the same level of risk, and that differences observed earlier in life may continue into the tenth decade. The research was supported by the National Institute on Aging of the National Institutes of Health.