A new study links long sleep duration to a blood marker tied to Alzheimer’s, raising questions about cause and effect.
Most health guidance treats extra sleep as a win, but a new study is complicating that assumption. Researchers found that adults sleeping more than 8.5 hours a night showed higher levels of a blood biomarker tied to Alzheimer’s disease, suggesting that unusually long naps may sometimes function as an early warning sign rather than a sign of good rest.
Inside the study
The research, published in the journal Alzheimer’s and Dementia, drew on data from 2,410 participants in the long running Framingham Heart Study, with an average age of 70. Investigators found that people who reported sleeping longer than 8.5 hours had elevated levels of p-tau181, a biomarker associated with Alzheimer’s related brain changes. The pattern grew more pronounced among those sleeping 10 hours or more, and long nappers in the study also tended to be older and to have higher rates of depression and existing dementia diagnoses.
Cause or symptom
Neurologist Steven Allder said the findings add to a growing body of evidence connecting shifts in sleep to some of the earliest biological processes involved in Alzheimer’s disease. He cautioned that the relationship likely runs in more than one direction, since early Alzheimer’s pathology can itself disrupt normal sleep, while disturbed or inefficient nap can separately show up as unusually long time spent in bed. Allder noted that duration alone says little about quality, and that someone spending nine or ten hours asleep may still be getting fragmented, poor quality rest that fails to support the brain’s normal restorative processes.
Postdoctoral researcher Vanessa Young echoed that uncertainty, saying the study makes clear that more sleep is not automatically better for brain health. She said the open question, whether long nap duration causes cognitive decline or simply reflects an early symptom of it, will require further research to resolve.
Why catching it early matters
Alzheimer’s disease still has no cure, which makes early detection especially valuable. Identifying the condition sooner gives patients access to disease modifying treatments such as lecanemab and donanemab, and gives families more time to plan for care. Findings like this one add another potential signal doctors could eventually use, alongside existing tools, to flag risk before symptoms become obvious.
What to do with this information
The study does not suggest that everyone who naps nine or ten hours is on a path toward Alzheimer’s, and researchers are careful to stress that the link is still being worked out. Good sleep hygiene remains a reasonable goal regardless of how the underlying science shakes out.
That means keeping a consistent sleep and wake schedule, creating a dark, cool and quiet bedroom, avoiding caffeine and heavy meals close to bedtime, staying physically active during the day and cutting back on screen time in the evening. For anyone noticing a significant, unexplained shift toward longer sleep, especially alongside memory changes or mood shifts, the findings offer one more reason to bring it up with a doctor rather than assume more rest is always the safer bet.
