Sleep Brainwaves May Temper A Chemical Tied To Alzheimer’s

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.

Stronger Sleep Brain Activity Weakened Orexin’s Link to Cognitive Decline

Looking at orexin and sleep activity together produced the main finding. In patients with stronger spindle or slow wave activity, higher orexin was less tightly tied to worse test scores. In one case, higher orexin went with worsening behavioral symptoms overall, but in patients with more frequent spindles, that pattern reversed. That cushioning appeared across overall thinking, verbal memory, and visual memory, and on the dementia screening test it showed up at every checkup from the start through three years.

Cushioning of this kind persisted after researchers adjusted for amyloid and tau, two Alzheimer’s-related proteins in spinal fluid, and for sleep apnea severity. Higher orexin also weakened the benefits linked to strong sleep activity, so the relationship ran both ways.

Orexin-Blocking Sleep Drugs Are Not Yet Shown to Slow Alzheimer’s

Medicines that block orexin are already approved for insomnia, and some are being studied in people with dementia. This study was observational, so it cannot show that orexin drives decline or that sleep rhythms protect anyone. Higher orexin might be partly the brain compensating for damage, in which case blocking it too aggressively could backfire. Future trials will need to weigh dose, timing, and which patients to treat. Dang-Vu pointed to “new ways to potentially act on sleep to slow the progression of Alzheimer’s disease.”

Only 60 people took part, with no healthy older adults for comparison, so it remains unclear whether the patterns are specific to Alzheimer’s or simply reflect aging. Sleep was recorded for a single night, and about 45% of participants had severe sleep apnea, a breathing condition that disrupts sleep.

In people already living with Alzheimer’s, stronger sleep brain activity went along with a weaker connection between orexin and worse thinking and behavior. That makes sleep quality a reasonable target for future trials, but whether improving it would actually slow the disease is still unknown.

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Disclaimer: This article is for general information only and is not medical advice. The study it describes is observational, so its findings show associations, not cause and effect. Anyone with concerns about Alzheimer’s disease, sleep, or medications should talk with a qualified health care professional.

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