People who stop breathing during sleep may have higher accumulations of the toxic protein tau, a biological hallmark of Alzheimer's disease, in part of the brain that manages memory, navigation and perception of time. A preliminary Mayo Clinic study released Sunday, March 3, will be presented at the American Academy of Neurology's 71st Annual Meeting in Philadelphia May 4-10.
Recent evidence has supported an association between an increased risk for dementia and sleep disruption. That's particularly true for obstructive sleep apnea, which is a potentially serious disorder where breathing repeatedly stops during sleep. However, it remains unclear what could be driving this association.
Using the population-based Mayo Clinic Study of Aging, researchers identified 288 people 65 and older who did not have dementia. Their bed partners were asked whether they noticed if their partners stopped breathing during sleep. Positron emission tomography brain scans of study participants looked for buildup of the toxic protein tau in the entorhinal cortex, which is the part of the brain that is deep behind the nose and susceptible to accumulating tau. The entorhinal cortex stores and retrieves information related to visual perception and when experiences happen. The dysfunctional tau protein forms tangles in the brains of people with Alzheimer's disease, contributing to cognitive decline.
Fifteen percent of the study group, or 43 participants, had bed partners who witnessed sleep apnea. Participants with witnessed apneas had about 4.5 percent higher levels of tau in the entorhinal cortex than those who have not been observed to have apneas during sleep. To reduce the effect of confounding variables, researchers controlled for several other factors that affect tau levels in the brain, such as age, sex, education, cardiovascular risk factors and other sleep complaints.
"Our research results raise the possibility that sleep apnea affects tau accumulation," says Diego Z. Carvalho, M.D., first author and neurology fellow at Mayo Clinic.
"But it's a chicken and egg problem," he notes, pointing to questions of which comes first as an underlying cause. Does sleep apnea cause an accumulation of tau, a toxic protein that forms into tangles in the brains of people with Alzheimer's disease? Or does the accumulation of tau in certain areas cause sleep apnea? "Longer studies are now needed to solve this problem."
Study limitations included a lack of sleep studies to confirm sleep apnea and its severity, and a lack of information about participants' sleep apnea treatment.