A new study tracked more than 800 adults who had already reached age 90 without a dementia diagnosis. I think the question they were asking is one a lot of us have probably wondered about. If you make it to 90 with your cognition intact, are you home free?

The short answer is no. Not entirely.

Over the course of follow-up, one subset of participants had roughly double the dementia risk of the others. The full details of what separated the higher-risk group from the lower-risk group aren't laid out in the source coverage, but the core finding stands on its own. Even after 90, dementia can still develop, and the risk is not the same for everyone.

The study, covered by Newsweek, adds to a growing area of research into how dementia operates in the oldest segment of the population. We still have a lot to learn about what happens with cognitive health in our 90s and beyond.

One thing the study makes clear is that dementia risk doesn't plateau at some magic age. The disease process can continue well into your 90s. My mother-in-law is 93 and sharp as a tack, and I'll admit I always assumed that meant she was simply past the window of risk. This research suggests that assumption deserves more nuance.

What I find most interesting is how little we actually know about the oldest-old population when it comes to brain health. Most dementia research has historically focused on people in their 60s and 70s. Studies like this one are starting to fill in the picture for those who've already outlived the average life expectancy. Which factors matter most at that stage, and which ones become less relevant, are still open questions.

The practical takeaway is limited but important. Reaching 90 with your mind intact is something to celebrate, but not a reason to stop paying attention. The risk hasn't disappeared, and researchers are still working to understand why some nonagenarians stay cognitively healthy while others don't.