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Story at-a-glance

• Sleep apnea, especially during rapid eye movement (REM) sleep, causes oxygen drops that damage small brain vessels and raise dementia risk, often before cognitive symptoms become noticeable
• New research links REM-specific oxygen loss to white matter lesions and entorhinal cortex thinning, two key markers of early neurodegeneration in aging and Alzheimer’s disease
• Standard apnea scores like apnea-hypopnea index (AHI) often miss these deeper risks because they don’t measure oxygen depth or track when during sleep the damage occurs
• Long-term studies confirm that even mild, untreated apnea accelerates brain aging and disproportionately increases dementia risk in women compared to men
• Treatments like breathing machines, oral devices, and lifestyle changes reduce apnea severity and help preserve brain health by ensuring proper oxygen delivery during sleep

Sleep apnea is a disorder defined by repeated interruptions in breathing during rest, often without your awareness. These pauses last from a few seconds to over a minute and happen dozens or even hundreds of times each night. The most common form, obstructive sleep apnea (OSA), occurs when the muscles in the back of your throat fail to keep the airway open, triggering brief arousals from sleep that fragment your sleep cycle.1

OSA has become one of the most common sleep disorders, affecting nearly 1 billion people worldwide, with rates increasing significantly with age, weight gain, and certain body traits. Snoring is one recognizable sign, but many people with OSA remain undiagnosed for years, especially when symptoms like fatigue, forgetfulness, or mood changes are mistaken for normal aging or stress.2

However, OSA does far more than just cause daytime sleepiness, especially when it disrupts the deeper stages of rest. Recent research from the University of California, Irvine, reinforces the strong association between sleep apnea and subtle but significant brain damage in areas that support memory and cognition.3 Understanding this link may prove vital for protecting your brain as you age.

Why Is REM Sleep Important?

REM sleep is when your brain does some of its most important work — processing emotions, consolidating memory, and regulating mood. It is named for the quick, darting eye movements that occur during this phase, which are accompanied by elevated brain activity, irregular breathing, and near-total muscle paralysis. Although it makes up a smaller portion of total sleep time compared to non-REM sleep, REM is essential.4

• The timing of REM matters — In a typical sleep cycle, REM occurs about 90 minutes after falling asleep and recurs every 90 to 120 minutes thereafter. Early in the night, REM stages are short, but they lengthen with each successive cycle. By the early morning hours, REM lasts 30 minutes or longer at a time.5

This pattern makes the later stages of sleep disproportionately important for memory consolidation, problem-solving, and emotional processing. Interruptions during this period have a far greater impact on cognitive function than disruptions in earlier, lighter stages of sleep.

• REM causes temporary paralysis of most voluntary muscles — This phenomenon is known as atonia, a protective feature that prevents your body from acting out dreams.6 However, this also causes muscle tone in the upper airway to drop significantly, making the throat more prone to collapse.

As a result, breathing becomes less stable during this stage, even in people who have no formal diagnosis of sleep apnea. For those who do, REM is the period when breathing is most likely to become labored or completely obstructed.7

• REM sleep is when the brain performs its most intensive housekeeping work — During this stage, the brain replays and reorganizes information gathered during the day. Experiences are sorted, stored, or discarded, and emotionally charged events are processed to reduce reactivity and stress. This mental recalibration supports learning, creativity, and psychological resilience.8

• REM has been a focus of aging and dementia research — Disruption of REM sleep has been associated with earlier onset of cognitive decline and structural changes in brain regions like the hippocampus and prefrontal cortex. These effects may not be immediately noticeable but accumulate over time.

Even in healthy adults, a consistent lack of uninterrupted REM sleep weakens attention span, impairs recall, and increases sensitivity to stress. The brain’s long-term resilience depends in part on getting enough of this stage and protecting it from disruption. This is where sleep apnea becomes especially concerning.

• The standard apnea score fails to detect this hidden risk — Clinicians typically rely on the apnea-hypopnea index (AHI), which counts the number of breathing disturbances per hour of sleep, to determine the presence and severity of OSA.

However, AHI does not differentiate between sleep stages or account for how long oxygen levels remain low. Someone with a modest AHI score may still experience prolonged and deep desaturations, specifically during REM sleep. These episodes escape detection yet carry meaningful health consequences.9

REM Sleep Oxygen Loss Predicts Early Brain Damage

All stages of sleep can be affected by sleep apnea. However, not all disruptions are equal in their consequences. In the featured study, published in the journal Neurology, researchers found that low oxygen levels during REM sleep were strongly linked to damage in the brain’s small blood vessels. This type of injury, known as cerebral small vessel disease, is a leading contributor to cognitive decline in older adults and often develops without early symptoms.10,11

• Oxygen saturation during REM sleep was a key factor predicting white matter injury — Researchers tracked 37 older adults with an average age of about 73 years, all cognitively unimpaired at the time of testing. Many had mild to moderate sleep apnea, with AHI scores ranging from 0 to 80. Despite these varied AHI scores, the most consistent predictor of brain changes was not the number of breathing interruptions but the depth of oxygen loss during REM sleep.

• Lower oxygen levels during REM sleep were linked to greater total white matter hyperintensity (WMH) volume — WMHs are visible signs of damage to the brain’s communication pathways. They appear as bright lesions on MRI scans and reflect restricted blood supply or small vessel leakage. WMHs are strongly linked to memory loss, executive dysfunction, and increased dementia risk, and are now recognized as an early sign of vascular brain aging.

• REM-specific oxygen loss also predicted WMH burden in specific brain regions — The more severe the oxygen drop, the greater the volume of white matter hyperintensities in the frontal and parietal lobes, which are regions responsible for attention, working memory, planning, and spatial reasoning.

These are the very functions that support complex thought, day-to-day decisions, and independent living. This targeted pattern of damage strengthens the view that REM-related hypoxemia (low oxygen levels in the blood) compromises the brain systems that manage higher-order cognition.

• The impact of low oxygen levels went beyond blood vessel damage — Higher frontal WMH burden linked REM to thinning of the entorhinal cortex, a key memory region and one of the earliest affected in Alzheimer’s disease. This structural loss, in turn, predicted poorer performance on a memory test designed to measure subtle overnight recall. Study author Bryce A. Mander, Ph.D., from UC Irvine, noted:

“Our findings may partially explain how obstructive sleep apnea contributes to cognitive decline associated with aging and Alzheimer's disease through the degeneration of brain regions that support memory consolidation during sleep.”12

• Oxygen loss during REM sleep is a distinct and often overlooked risk factor — Standard sleep apnea metrics like AHI miss both the depth of oxygen drops and the brain’s heightened vulnerability during specific sleep stages. These findings suggest that REM-related desaturation deserves closer scrutiny, even in cases labeled as mild. Monitoring how far and when oxygen levels fall may help identify those most at risk for lasting brain damage.

Learn more about the risk factors, symptoms, and other health risks of sleep apnea in “Understanding the Causes and Symptoms of Obstructive Sleep Apnea.”

Long-Term Studies Support the Silent Brain Damage of Sleep Apnea

The UC Irvine study is just part of a growing body of research connecting sleep-related oxygen loss with structural brain damage. One of the most comprehensive efforts to date, a 10-year longitudinal study published in Sleep Advances, evaluated 18,815 adults over the age of 50 to determine how OSA and nighttime oxygen instability contribute to dementia risk.13

• This study documented how brain damage accumulates over time — Unlike earlier research based on single-timepoint imaging, this study used serial MRI data to observe white matter changes as they progressed. Among participants with moderate to severe OSA, lower minimum oxygen saturation during sleep predicted significantly faster accumulation of WMHs.

These associations held even after accounting for age, blood pressure, diabetes, and other vascular risk factors, pointing to nocturnal hypoxemia as an independent driver of small vessel brain damage.

• Brain deterioration began before symptoms were obvious — Many participants showed no signs of cognitive decline at baseline, yet with known or suspected sleep apnea steadily increased over the 10-year period. This silent progression reinforces the importance of identifying and addressing OSA early, before cognitive deterioration progresses past the point of recovery.

• OSA-related dementia risk was especially pronounced in women — One striking outcome of the study was the discovery of a sex-specific pattern. Women with known or suspected OSA had a significantly higher cumulative risk of dementia than their male counterparts at every age measured.

By age 80, women with OSA showed a 3.7% greater risk compared to those without, while men showed a 2.1% increase. These differences remained statistically significant even after adjusting for education, race, and relationship status.

• OSA was identified as a modifiable contributor to dementia — The authors concluded that sleep apnea represents a major, underrecognized pathway to dementia — one that is both preventable and treatable. They wrote:

“These population-based data implicate a common midlife sleep disorder as a significant risk factor for dementia onset, with disproportionate impact on women. Our findings offer new evidence of a sleep-based pathway that underlies sex-specific differences in dementia risk. Further, as OSA is a treatable condition, this study illuminates the impact of a potentially modifiable yet frequently overlooked risk factor for dementia.”14

For a closer look at how sleep apnea affects women’s brain health, see “Sleep Apnea Raises Dementia Risk in Older Women.”

How Is Sleep Apnea Treated?

Treating obstructive sleep apnea means keeping your airway open during sleep to prevent the repeated breathing interruptions that strain your body and brain. Several approaches exist, each suited to different severities and individual needs.

• CPAP therapy remains the standard treatment — Continuous positive airway pressure (CPAP) delivers a constant stream of air through a mask to keep your airway from collapsing while you sleep. Many people experience significant symptom relief, but CPAP was never meant to be a lifelong solution.15

According to its inventor, Dr. Colin Sullivan, it was designed as a stopgap — something to use while addressing root causes like excess weight, structural airway issues, or underdeveloped jaw anatomy.16 Despite its effectiveness, CPAP can be difficult to tolerate. Common complaints include claustrophobia, nasal blockage, dry mouth, and skin irritation from the mask.17

• Oral appliances — Mandibular advancement devices (MADs) are custom-made mouthpieces that gently shift the lower jaw forward. This movement helps prevent the tongue and soft tissues from blocking the airway during sleep. MADs are fitted by dentists trained in dental sleep medicine and often prescribed in collaboration with sleep specialists to avoid unwanted side effects like jaw pain or misalignment.18

• Orofacial myofunctional therapy (OMT) — OMT uses targeted exercises to retrain the muscles of the mouth, face, and throat. It focuses on correcting tongue position, improving nasal breathing, and supporting proper chewing, swallowing, and posture. This approach is especially effective for mild to moderate OSA and offers lasting structural improvements without devices or surgery.19

• Emerging therapies target muscle tone and breathing patterns — Neuromuscular electrical stimulation (NMES) devices are worn briefly each day and use gentle pulses to strengthen the muscles of the tongue and upper airway, reducing the risk of collapse during sleep. In more advanced cases, surgical options, like maxillomandibular advancement (moving the upper and lower jaw forward), are considered to physically enlarge the airway.

In addition, training yourself to breathe through your nose instead of your mouth helps regulate breathing volume and supports better oxygen delivery to your tissues and brain, which is an often overlooked but essential strategy in sleep apnea care.20

Learn more about how these alternatives compare to CPAP machines in “Why Is Everyone on CPAP Machines?”

Targeted Lifestyle Changes That Reduce Sleep Apnea Severity

Making specific lifestyle changes meaningfully reduces the severity of obstructive sleep apnea and improves overall sleep quality. While some individuals may still require medical treatments like CPAP or mandibular advancement devices, addressing underlying contributors helps reduce nighttime airway obstruction and supports more lasting, sustainable relief.

• Retrain your breathing habits — Dysfunctional breathing patterns, such as mouth breathing, shallow upper chest breathing, or over-breathing during rest, worsen sleep-disordered breathing by disrupting carbon dioxide balance and lowering airway tone. Working with a breathing behavior specialist will help you identify habitual breathing errors, retrain nasal breathing, and restore proper rhythm. Even during the day, how you breathe shapes how well you sleep.

• Reach and maintain a healthy weight — Excess fat around the neck, jaw, and upper airway increases pressure on soft tissues and narrows the airway. If you are overweight or obese, losing even 10% of your body weight leads to noticeable improvements in sleep apnea symptoms.

• Change your sleep position — Positional sleep apnea occurs when the airway collapses more often in certain positions, especially when lying on the back. Gravity pulls the tongue and soft palate backward, narrowing or blocking airflow. Sleeping on your side or stomach, or elevating the upper body with a wedge pillow, reduces obstruction significantly.

For people who unknowingly shift to their back during sleep, positional trainers, specialty pillows, or even a tennis ball sewn into the back of sleepwear can help prevent it.

• Avoid alcohol and smoking — Alcohol relaxes the muscles of the upper airway, making them more prone to collapse during sleep. Smoking inflames and irritates the lining of the airway, causing swelling and mucus buildup that narrows breathing passages. Avoiding these habits improves oxygen saturation and reduces apneic episodes, while also benefiting cardiovascular health and lung function, both of which are commonly strained in people with OSA.

• Eliminate sedatives and benzodiazepines when possible — Medications that depress the central nervous system, such as benzodiazepines and other sleep-inducing drugs, reduce muscle tone in the airway and dull the brain’s responsiveness to oxygen drops.

This combination increases the risk of prolonged apnea episodes. If you rely on these medications for sleep, consult your physician about non-sedative alternatives such as magnesium, L-theanine, or sleep-focused cognitive behavioral therapy.

Lifestyle interventions are not just complementary — they are foundational. By addressing these factors, you actively improve your sleep quality, reduce the severity of apnea episodes, and lower the risk of long-term cognitive decline linked to untreated OSA.

Frequently Asked Questions (FAQs) About Sleep Apnea and Cognitive Health

Q: What is obstructive sleep apnea (OSA)?

A: OSA is a common sleep disorder in which your airway repeatedly collapses during sleep, causing breathing to stop and restart, often without your awareness. These episodes occur multiple times per night, disrupting deep sleep and reducing oxygen levels. OSA is most common in older adults, people with excess weight, and those with certain anatomical features like a narrow airway or recessed jaw.

Q: Why is REM sleep so important for brain health?

A: REM sleep is the stage when your brain consolidates memory, processes emotions, and restores psychological resilience. It’s marked by high brain activity, irregular breathing, and muscle paralysis. Because REM periods lengthen later in the night, disruptions during this phase interfere with cognitive function, stress regulation, and long-term mental clarity.

Q: How does sleep apnea affect REM sleep?

A: REM sleep naturally causes muscle tone to drop, including in the upper airway, which makes breathing less stable. In people with sleep apnea, this leads to more frequent or deeper oxygen drops during REM. This stage-specific vulnerability makes REM-related oxygen loss especially harmful to brain structure and function.

Q: Does sleep apnea increase your risk for Alzheimer’s disease?

A: Yes. REM-specific oxygen loss has been linked to thinning of the entorhinal cortex, a key region involved in memory and one of the first affected in Alzheimer’s disease. Studies have shown that even in people without current cognitive symptoms, these structural changes are already underway if sleep apnea is left untreated.

Q: Can lifestyle changes reduce sleep apnea severity?

A: Yes. Addressing key factors like body weight, breathing habits, airway inflammation, and sleep position significantly reduces apnea episodes. Nasal breathing retraining, avoiding alcohol and sedatives, quitting smoking, and maintaining healthy sleep posture all support better airway stability and long-term brain protection.

Sources and References

• 1 Mayo Clinic, Sleep Apnea
• 2 Cleveland Clinic, Sleep Apnea
• 3, 9 UC Irvine News, May 7, 2025
• 4, 5 Cleveland Clinic, Sleep
• 6 Science Direct, Muscle Atonia
• 7 J Clin Sleep Med. 2020 Mar 15;16(3):377-384
• 8 Sleep Foundation, July 3, 2025
• 10 Neurology. 2025 Jun 10;104(11):e213639
• 11, 12 Science Daily, May 7, 2025
• 13, 14 SLEEP Advances, Volume 5, Issue 1, 2024, zpae077
• 15 SleepApnea.org, Treatment for Obstructive Sleep Apnea
• 16 Salon, October 23, 2023
• 17 Sleep Foundation, July 10, 2025
• 18 Cleveland Clinic, Oral Appliances for Sleep Apnea
• 19 Sleep. 2015 May 1;38(5):669-675
• 20 ERJ Open Res. 2023 Dec 27;9(6):00474-2023