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• Study participants — The study involved 12 adults between 40 to 64 years old with moderate to severe untreated obstructive sleep apnea. All participants were otherwise healthy, free of medications, and had stable sleep-wake schedules prior to joining the study. They were also rigorously screening to ensure no confounding factors such as cardiovascular disease (CVD), smoking, recent travel across time zones, or shift work, would affect the results.

• Conducting the experiment — Over five days, participants lived in a time-isolated environment inside a sleep laboratory at OHSU’s campus; the lab was free of natural light or time cues. After a baseline day, they followed a schedule consisting of 10 repeating sleep cycles of 5-hour 20-minute periods (these were divided into 2 hours 40 minutes of sleep in darkness and 2 hours 40 minutes of wakefulness).

This manipulated schedule forced participants’ behavioral cycles (sleep/wake, meals and activity) to occur at all circadian phases. Meanwhile, their internal circadian clock free-ran at its natural rhythm, measured through repeated dim-light melatonin onset (DLMO) assessments. This design made it possible to determine whether changes in vascular function were driven by circadian biology rather than sleep, posture, meals, or the apnea episodes themselves.

• Measuring the blood vessel function — Each participant had their blood vessel function checked 10 times during the study, at different points in their internal circadian cycle. This was done using a standard ultrasound test called flow-mediated dilation (FMD). The test looks at two things: the size of the artery at rest and how much the artery widens after blood flow is temporarily increased.

To make sure the results were fair, the researchers also calculated what’s called shear-normalized FMD, which adjusts the measurements so they aren’t affected by differences in how strong the blood-flow increase was.

• Measuring sleep and breathing — During every sleep period, the researchers used polysomnography (a full sleep study) to track the participants’ sleep duration, sleep efficiency, and their Apnea-Hypopnea Index (AHI), which refers to how often breathing stopped or became shallow.

• The worst blood vessel function happened around 3:00 a.m. — During this time, the arteries were least able to widen, pointing to a higher cardiovascular risk. The change was significant — about an 82% difference from peak to low point. This is considered meaningful for heart and blood vessel health.

• The same pattern was seen even after adjusting for differences in blood flow — This shows that the drop at night wasn’t caused by weaker blood flow but by a real dip in endothelial function. The resting artery size also did not change across the day, meaning the problem wasn’t the size of the artery itself — rather, the issue was specifically how well the artery could respond and dilate.

• Vascular issues were seen even in participants without additional complicating medical conditions — This is important because it tells you these effects do not rely on severe heart disease or diabetes to appear; rather, they emerge directly from untreated apnea and the way your circadian system behaves if you have this condition.

• Sleep apnea fundamentally disturbs the body’s internal clock — When you have sleep apnea, you experience repeated pauses in airflow that cause drops in blood oxygen and frequent micro-arousals throughout the night. This is because every time breathing stops, oxygen levels fall sharply, leading the brain to respond with a surge of stress signals to wake you just enough to reopen the airway. These events can happen dozens or even hundreds of times per night.

Beyond fragmenting sleep, this cycle of oxygen deprivation and arousal sends powerful physiological “shock waves” through the body. Over months and years, this repeated stress begins to disrupt not just sleep, but the timing cues that keep the body’s systems running in harmony.

• Sleep apnea leads to disruption at the molecular level — Perhaps the strongest evidence of circadian disturbance comes from the molecular data. Inside every cell, a network of “clock genes” — including BMAL1, PER1, and CRY2 — loops through a 24-hour cycle, turning on and off in a tightly regulated rhythm. These genes coordinate the timing of metabolism, cardiovascular activity, hormone release, and immune function.

However, in people with sleep apnea, the clock gene expression falls out of rhythm and loses its normal rhythmic pattern. This misalignment creates a kind of internal circadian chaos, where the signals that normally keep organs synchronized fall out of step.

• There are several interconnected biological pathways that cause circadian dysregulation to directly harm the cardiovascular system — For example, repeated drops in oxygen activate a key molecular sensor called hypoxia-inducible factor-1 alpha (HIF-1α). Normally, HIF-1α helps the body adapt to occasional low-oxygen situations.

But in sleep apnea, it becomes elevated night after night, which creates long-term harm as it triggers inflammation, impairs, vascular function, accelerates atherosclerosis, and raises blood pressure levels.

• Sleep apnea also activates nuclear factor kappa B (NF-κB) — This is an inflammatory mediator. Think of it as a “master switch” for inflammation. Basically, your immune system stays in high-alert mode every night. NF-κB activation also leads to a surge in inflammatory chemicals, such as TNF-α, IL-6, and C-reactive protein (CRP), which damage blood vessels, raise blood pressure, and contribute to plaque formation.

• Sleep apnea leads to abnormal blood pressure — A healthy cardiovascular system follows a clear daily pattern. During sleep, blood pressure and heart rate drop — this is vital, as it gives blood vessels time to recover from daytime stress. However, sleep apnea not only prevents this dip from occurring, but it actually causes the opposite — elevating your blood pressure at night.

• The study participants — To conduct the study, the researchers used two sets of databases. They used data from 9,320 participants from the U.S. National Health and Nutrition Examination Survey (NHANES) and 7,637 individuals from the China Health and Retirement Longitudinal Study (CHARLS).

• Those with CircS were significantly more likely to die early from metabolic diseases — In both groups, individuals with CircS were older and carried heavier burdens of chronic illness, including heart disease, hypertension, and diabetes.

• The risk wasn’t limited to metabolic conditions — People with CircS also faced higher death rates from Alzheimer’s, cancer, and even common infections like pneumonia. The pattern was especially higher in adults between 40 and 60 years old, where the risk stayed elevated across nearly every major cause of death.

“This study is the first to show a strong, consistent association between CircS and both all-cause and cause-specific mortality in large, diverse cohorts … CircS likely disrupts biological functions performed by vascular, inflammatory, metabolic, and other systems, increasing vulnerability to chronic diseases and premature death,” News-Medical.net reports.⁷

• Continuous positive airway pressure (CPAP) therapy — CPAP works by delivering a constant stream of air through a mask to keep your airway from collapsing while you sleep. But while many have experienced improvements in their symptoms, CPAP was never meant to be a lifelong solution.⁸ Even the featured study found that some individuals with sleep apnea do not tolerate this treatment.⁹

Rather, CPAP was designed as a stopgap — it’s meant to be used while addressing root causes like obesity, or issues with the airway or jaw anatomy.¹⁰ CPAP can also cause discomfort, as those who use it complain of effects like claustrophobia, nasal blockage, dry mouth, and skin irritation from the mask.¹¹

• Mandibular advancement devices (MADs) — These are custom-fitted mouthpieces designed to move the lower jaw slightly forward while you sleep. This forward positioning helps keep the tongue and soft tissues from collapsing into the airway, reducing breathing interruptions.

MADs are created by dentists who specialize in dental sleep medicine and are typically prescribed in coordination with a sleep specialist to minimize potential side effects such as jaw discomfort or changes in bite alignment.¹²

• Orofacial myofunctional therapy (OMT) — This therapy involves doing targeted exercises that strengthen and retrain the muscles of the mouth, tongue, face, and throat. OMT helps correct tongue posture, promotes nasal breathing, and supports healthier chewing, swallowing, and overall airway function. Those with mild to moderate sleep apnea can benefit from this, as it creates lasting structural improvements without the need for devices or surgery.

• Neuromuscular electrical stimulation (NMES) devices — These devices use a removable mouthpiece worn for about 20 minutes a day, while awake, over a six-week period. The gentle electrical stimulation helps strengthen and tone the tongue and upper airway muscles, reducing the likelihood that these tissues will collapse during sleep.

• Surgical intervention — In some cases, surgery may be recommended to widen the upper airway. This is often done by repositioning the upper and lower jaw forward, creating more space and improving airflow during sleep.

• Retrain your breathing habits — Breathing through your mouth, shallow upper chest breathing, or over-breathing during rest all worsen your nighttime breathing by disrupting carbon dioxide balance and lowering airway tone. Train yourself to breathe through your nose instead. This allows for optimal oxygenation of tissues and organs, including your brain.

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.

• Address obesity — Having 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.

• Adjust your sleep position — Positional sleep apnea happens when the airway is more likely to collapse in certain sleeping positions, especially when lying on the back. When you sleep like this, gravity causes the tongue and soft palate to fall backward, narrowing or blocking airflow. Instead, try sleeping on your side or stomach, or use a wedge pillow to elevate your upper body. This helps reduce this type of obstruction.

If you unknowingly shift to their back during sleep, consider using positional trainers, specialty pillows, or even a tennis ball sewn into the back of your sleepwear to prevent it.

• Avoid alcohol and smoking — Alcohol relaxes the muscles in the upper airway, increasing the likelihood of airway collapse during sleep. Smoking irritates and inflames the airway tissues, causing swelling and mucus buildup that further narrows the breathing passages. Reducing or eliminating these habits will improve oxygen levels, decrease apnea events, and support both cardiovascular and lung health — areas already under strain in people with sleep apnea.

• Eliminate sedatives and benzodiazepines when possible — These medications depress the central nervous system, reducing muscle tone in the airway and weakening the brain’s ability to respond to drops in oxygen. This combination can lengthen and worsen apnea episodes.

If you depend on these medications for sleep, talk with your physician about non-sedating alternatives such as magnesium, L-theanine, or cognitive behavioral therapy for insomnia (CBT-I).