Sleep Lab Study Links a Wakefulness Chemical to Alzheimer’s Onset
A bad night’s sleep can mean a groggy morning. For someone with Alzheimer’s disease, disrupted sleep may be tied to faster memory loss. A new study in Neurology centers on orexin, a brain chemical that keeps people awake and alert, and finds that higher levels in Alzheimer’s patients went along with faster mental decline and worse behavioral symptoms. Yet certain rhythms of brain activity during sleep appeared to weaken that link.
Sleep trouble affects up to two-thirds of people with Alzheimer’s, and researchers see it as both a result and a possible driver of the disease. Orexin helps control the shift between sleeping and waking. “Just as too little orexin is associated with diseases like narcolepsy, too much orexin can lead to higher vulnerability of Alzheimer’s,” said study co-author Thanh Dang-Vu, a neurologist and professor at Concordia University, in a press release. Earlier studies of orexin levels in Alzheimer’s patients were inconsistent, and few followed patients over time.
Hours of sleep did not account for orexin levels. Total sleep time and how much of the night someone spent awake showed no clear connection to the chemical, pointing toward what the brain does during sleep rather than how long it sleeps.
Higher Orexin Levels Were Tied to Faster Alzheimer’s Decline
Researchers at a memory clinic in Lleida, Spain, enrolled 60 adults aged 60 and older, 30 women and 30 men, with an average age of 74.7. Each had mild-to-moderate Alzheimer’s confirmed with biological markers, and none were taking sleeping pills or other drugs that alter sleep activity. Participants spent one night in a sleep lab with their brain activity recorded, then gave a spinal fluid sample the next morning, drawn from the fluid around the brain and spinal cord, to measure orexin. Tests of memory, thinking, and behavior were repeated after a year, and a standard dementia screening test was given again at two and three years.
Patients with higher orexin at the start scored worse in follow-up testing on overall thinking, verbal memory, and visual memory, and showed more severe behavioral symptoms. Higher orexin also came with higher spinal fluid levels of two forms of tau, a protein linked to nerve cell damage in Alzheimer’s, and of YKL-40, a marker of brain inflammation.
Women averaged roughly 24% higher orexin than men. Researchers speculated that estrogen loss after menopause may be a factor, though the study could not test that.
Sleep Spindles and Slow Waves Tracked With Lower Orexin Levels
Recordings from the sleep lab focused on two kinds of activity during non-REM sleep, the light and deep stages outside dream-heavy REM sleep. Sleep spindles are quick bursts of rhythmic brain activity tied to storing new memories. Slow oscillations, or slow waves, are large, rolling electrical waves that travel across the brain, especially during deep sleep, and may help the brain clear out waste, though the researchers did not measure that process.
Patients with more frequent, stronger spindles and longer slow waves had lower orexin. Not every link survived a statistical check designed to weed out flukes, but the ones for spindle frequency, spindle strength, and slow wave length did.
Source : https://studyfinds.com/sleep-brainwaves-may-temper-alzheimers
