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The results of the small study hint that people with a higher-than-normal risk of Alzheimer's disease who had worse sleep quality, more sleep problems and daytime sleepiness had more markers for Alzheimer's disease in their spinal fluid than those who didn't have sleep issues.
The markers found by researchers included signs of the proteins amyloid and tau, and brain cell damage and inflammation, all linked to potential Alzheimer's.
Amyloid is a protein that folds and forms plaques. Tau is a protein that forms tangles. Plaques and tangles are found in the brains of those with Alzheimer's disease and are considered a hallmark of the disease.
"This study and others in the field suggest that sleep may be a modifiable risk factor for Alzheimer's disease," said senior researcher Barbara Bendlin. She's an associate professor of medicine at the University of Wisconsin School of Medicine and Public Health.
"This will require studies that directly test whether modifying sleep has a beneficial effect on the brain," Bendlin said.
So, if you're someone who's always tossing and turning at night, does that mean you're destined to a future with Alzheimer's disease?
Not necessarily. Bendlin said these findings cannot prove that poor sleep causes Alzheimer's disease. "We found an association," she said. "But that does not mean cause and effect."
It's possible changes in the brain associated with Alzheimer's could affect sleep, as opposed to the other way around, Bendlin added.
People with markers -- signs -- of Alzheimer's in their spinal fluid aren't necessarily predestined to develop the condition either, she said.
"We found relationships between sleep and levels of proteins related to Alzheimer's disease, but the proteins that we were measuring haven't yet been shown to predict future dementia when measured in cognitively healthy people," Bendlin said.
The study included 101 people and their average age was 63. At the time of testing, all of the study volunteers had normal thinking and memory skills. But they were considered at risk for Alzheimer's either because they had a parent with the disease or they carried a gene that increases the risk for Alzheimer's called apolipoprotein E, or APOE.
The study volunteers gave a sample of spinal fluid to be tested for markers of Alzheimer's disease.
They also answered questions to judge the quality of their sleep. Examples included: "During the past four weeks, how often did you get the amount of sleep you needed?" Or "Did you get enough sleep to feel rested upon waking in the morning?" Bendlin said.
Although a strong association between sleep problems and Alzheimer's markers was seen in most people, not everyone with sleep difficulty had these markers in their spinal fluid, Bendlin said.
For example, there was no association seen between people who had sleep apnea and markers for Alzheimer's in their spinal fluid.
Other factors -- such as the use of drugs to aid sleep, education, depression and weight -- didn't change the association between poor sleep and markers for Alzheimer's disease, the researchers found.
One thing that could have thrown the findings off is that the participants reported their own sleep problems. It's possible that people misreported their sleep issues or didn't remember them correctly, the researchers said.
One specialist said that the association between sleep and amyloid has been seen in mice, but its effect on people isn't clear.
"There is a positive feedback loop involving sleep and amyloid," said Dr. Sam Gandy, director of the Center for Cognitive Health at Mount Sinai Hospital in New York City.
In mice, the worse the sleep, the more amyloid builds up. The more amyloid builds up, the worse the sleep, he said.
It's not known if this occurs in the same way in humans, Gandy said.
"Since our ability to slow progression of Alzheimer's is still quite limited, this is an important area for research so that we might be able to exploit sleep regulation therapeutically," he said.
Bendlin said it's important to identify modifiable risk factors for Alzheimer's because delaying Alzheimer's disease in people by as little as five years could reduce the number of cases in the next 30 years by nearly 6 million and save $367 billion in health care costs.
The report was published online July 5 in the journal Neurology.
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SOURCES: Barbara Bendlin, Ph.D., associate professor, medicine, University of Wisconsin School of Medicine and Public Health, Madison; Sam Gandy, M.D., Ph.D., director, Center for Cognitive Health, Mount Sinai Hospital, New York City; July 5, 2017, Neurology, online