Poor sleep has been associated with Alzheimer's disease risk, but a new study suggests a specific aspect of sleep is important.
The study, involving 119 older adults (60+), of whom 80% were cognitively normal and the remainder very mildly impaired, found that decreased slow-wave sleep coincided with higher levels of tau in the brain and a higher tau-to-amyloid ratio in the cerebrospinal fluid.
Amyloid plaques and tau tangles develop for decades before cognitive symptoms of dementia emerge. Identifying the process at an early stage offers a possible window of opportunity for successful intervention.
Participants’ sleep at home was monitored over the course of a normal week, and participants also kept sleep logs of nighttime sleep and daytime napping. Thirty-eight people underwent PET brain scans for amyloid-beta and tau proteins, and 104 people underwent spinal taps to provide cerebrospinal fluid. Twenty-seven did both.
Those with increased tau pathology actually slept more, during both night and day, but their quality of sleep was poorer. In fact, daytime napping alone was significantly associated with high levels of tau, making it a useful indicator of risk.