When people hear about Alzheimer's they immediately think about memory loss, Lea Grinberg, professor of neurology at the University of California San Francisco told USA TODAY.
Grinberg and 18 other scientists from the University of California San Francisco, University of California, Berkeley and the University of Sao Paulo, among others, worked on the paper.
Researchers have previously found that people who develop Alzheimer's show changes in sleep years before their memory begins to decline, Grinberg said.
People who develop Alzheimer's tend to sleep more during the day, taking naps or feeling drowsy and dosing off. Sometimes, they wake up during the night; that's called fragmented sleep, Grinberg said.
If napping is a part of your routine on a regular basis though, you don't need to worry about taking an afternoon snooze, or mid-morning for that matter.
"It only gets worrisome when it represents a change," said Grinberg. "For instance, in some cultures, it is pretty common to nap every day. This is quite okay."
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Although researchers knew Alzheimer's disease and changes in a person's sleeping behavior were linked, the nature of this relationship has been unclear. Grinberg said researchers didn't know if the sleep changes could be a risk factor for Alzheimer's or a symptom of the disease.
"This new research suggests that sleep problems may be closely linked to the brain cell death seen in Alzheimer's," Heather Snyder, vice president of medical science relations at the Alzheimer's Association told USA TODAY.
The team looked at areas of the brain that promote awakening.
When they did, they found evidence that an entire network of neurons that keeps us awake is wiped out by the disease, Grinberg said.
They studied postmortem brain tissue of people who had donated their brain to research. Looking at the tissue after death is still the only reliable way to diagnose a neuro-degenerative condition.
Grinberg and her team examined postmortem tissue of 13 deceased Alzheimer's patients and compared them to others without the disease.
They found the destruction of "wakening neurons" happens in brains affected by Alzheimer's disease. In those brains, the three areas of the brain that keep us awake had lost up many of their neurons.
Researchers found "considerable amounts of tau inclusions" in the awakening areas of the brain, the study said.
Tau is a protein present in the neurons of all species. Its normal function is to stabilize a certain part of the neuron. However, in the brain of a person with Alzheimer's disease, tau becomes abnormal and instead destabilizes the neurons, researchers have found.
Accumulation of abnormal tau protein is one of the hallmarks of Alzheimer's disease, said Grinberg.
They don't know how long elapses between sleep pattern changes and memory loss. Grinberg said it happens with different levels of severity in different patients and may not affect some patients at all.
Their findings provide the foundation for clinical trials that will aim to answer questions raised by the new research, Grinberg said.
As a result of this study and one in the past, she said, they have received funding to keep looking into changes in sleep patterns before memory loss begins.
"The NIH and Rainwater Charitable Foundation are investing $1.4 million per year in our group to continue this research," she said.
While the published study focused on areas of the brain promoting awakening, researchers are now assessing other areas of the brain responsible for promoting sleep and the areas that regulate circadian rhythm.
Snyder said that more research is needed to understand the exact relationship between sleep and Alzheimer's. Making sure that you're getting good sleep though, she said, is one of the Alzheimer’s Association’s "10 Ways to Love Your Brain."
Follow Morgan Hines on Twitter: @MorganEmHines.
This article originally appeared on USA TODAY: Warning sign for Alzheimer's: Increased napping, says new research