Poor-quality sleep could be an early sign of Alzheimer’s disease in older adults, according to the findings of a new study, published Jan. 9 in the journal Science Translational Medicine.

Daytime napping alone was significantly associated with high levels of the toxic brain protein tau, meaning that asking a simple question — How much do you nap during the day? — might help healthcare professionals identify people who could benefit from further testing, according to the authors.

But sleep monitoring, they said, one day may offer an easy and affordable way to screen for deteriorating brain health earlier, if future research bears out the findings of their study.

“I don’t expect sleep monitoring to replace brain scans or cerebrospinal fluid analysis for identifying early signs of Alzheimer’s disease, but it could supplement them,” said first author Brendan Lucey, M.D., an assistant professor of neurology and director of the Washington University Sleep Medicine Center. “It’s something that could be easily followed over time, and if someone’s sleep habits start changing, that could be a sign for doctors to take a closer look at what might be going on in their brains.”

Lucey and colleagues studied 119 people aged at least 60 years, 80% of whom had normal cognition; the remainder had cognition that reportedly was very mildly impaired. Study participants wore portable electroencephalogram, or EEG, monitors and wristwatch-like sensors to track body movements, kept sleep logs in which they noted when they slept at night and napped during the day, and underwent tests to measure levels of amyloid beta and tau in their brains and cerebrospinal fluid.

The researchers found that older people who have less slow-wave sleep, which is the deep sleep people need to consolidate memories and wake up feeling refreshed, have higher levels of the brain protein tau. Elevated tau is a sign of Alzheimer’s disease and has been linked to brain damage and cognitive decline.

“The key is that it wasn’t the total amount of sleep that was linked to tau; it was the slow-wave sleep, which reflects quality of sleep,” Lucey said. “The people with increased tau pathology were actually sleeping more at night and napping more in the day, but they weren’t getting as good quality sleep.”