You might recall that researchers recently connected poor sleep with raised levels of tau in the brain. Sleep is needed to clear out tau, the amount of which rises during the active use of the brain while waking. Altered forms of tau protein can aggregate in the aging brain to form the neurofibrillary tangles that occur in later stages of Alzheimer's disease, and this might explain some of the known correlation between sleep disruption and neurodegeneration. The study here provides more data on this correlation, linking higher levels of tau with sleep apnea specifically, a common form of sleep disturbance. This is still a correlation in search of definitive proof of causation in humans, however, even if the recent animal study seems fairly compelling on the point of poor sleep causing raised tau levels.
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. 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. "Our research results raise the possibility that sleep apnea affects tau accumulation. But it's a chicken and egg problem." 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?