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  • Sleep apnea is a common sleep disorder among US adults.
  • Previous research has linked sleep apnea-induced oxygen deprivation to increased dementia risk.
  • New findings indicate that the fluctuation in oxygen levels is a critical factor in brain cell death.
  • Lessons can be taken from this mice-based study, but more human-led investigations are needed.

Sleep apnea — a disorder that causes breathing to stop and start during sleep — has long been linked to increased dementia risk and cognitive decline.

Previous research has explored how and why oxygen deprivation during sleep has a detrimental influence on cognitive decline. Now a new study conducted by Australian scientists has built on these investigations.

“There have been epidemiological data that suggested hypoxia and dementia were linked, but it’s hard to work out the comorbidities,” stated Elizabeth J Coulson, PhD, head of school, School of Biomedical Sciences Faculty of Medicine at the University of Queensland and co-author of the study. 

Hypoxia occurs when the body does not have enough oxygen to keep tissues healthy.

The new findings highlight that intermittent oxygen deprivation occurring from sleep apnea “can cause neuronal loss of cells that we know die in dementia,” she said. “Hence, we may have found a mechanism for a known risk.”

What the study involved

The trial was conducted on mice, rather than humans, and researchers created a disordered sleeping scenario mimicking sleep apnea — involving disruption, altered breathing, and moderate hypoxemia (low oxygen blood levels). 

As a result, the mice showed increased cognitive impairment and pathological features associated with Alzheimer’s disease. Their brains also experienced other symptoms.

These included the following:

  • Higher levels of inflammation — which is associated with neurological impairment
  • Selective degeneration of cholinergic basal forebrain neurons — linked to functions such as learning and memory 
  • Increased amounts of beta-amyloid — a type of plaque commonly seen in Alzheimer’s patients

“Imagine [the plaque] to be like the deposits in your plumbing,” explained Dr. Abhinav Singh, medical director of Indiana Sleep Center, medical expert at SleepFoundation.org, and author of Sleep to Heal

“Hard-water related deposits can slow the flow of water in the piping and eventually block and damage it,” he shared. 

However, the pathological features linked to dementia were not seen when blood oxygen levels were restored during sleep.

Importantly, the researchers believe how oxygen is restricted may play a critical role in cognitive decline. 

“Our data suggest it is the fluctuations up and down in oxygen levels that is the cause,” Coulson told Healthline.

Yet, when it comes to neuron degeneration, “we don’t know exactly how often or how low the oxygen needs to go, or for how long, and whether it is cumulative or not,” she continued. 

“Our bodies can adjust to longer periods of hypoxia, but not to the fluctuations — that’s about as much as we know. These are the next things we are looking at.”

How oxygen impacts the brain

We know the influence oxygen deprivation can have on the brain, but how are the two elements connected?

“Your nervous system, which comprises your brain, spinal cord, and the nerves that come off the spousal cord and connect to the body, needs oxygen to function,” explained Louisa Nicola, neurophysiologist and female human performance expert for Momentous. 

“Your brain gets its oxygen delivery from blood supplied through a web of capillaries — or microvessels — which permeate brain tissue,” she continued. But, “when the brain doesn’t get enough oxygen, brain cells begin to die.”

The brain requires more oxygen than you might expect. “[It] uses about a fifth of your body’s total oxygen supply,” Nicola revealed to Healthline.

Oxygen isn’t only critical in preventing brain cell death: it can also help manage other cognitive factors that contribute to dementia.

“Studies show that Alzheimer’s and dementia patients have an accumulation of tau protein, which leads to cognitive decline,” Dr. Jyoti Matta, interim chair for medicine, pulmonologist, and sleep specialist at Jersey City Medical Center in New Jersey, told Healthline.

“Good-quality, deep, slow-wave sleep allows for clearance of all these toxic proteins,” she continued — and this is not achieved among those with sleep apnea.

What can be learned from the study

Even though this research was conducted on mice, we can still take important lessons from the findings in understanding sleep apnea and dementia in humans. 

“There is a lot of evidence that links sleep apnea to Alzheimer’s disease risk,” added Bryce Mander, Ph.D, assistant professor, Psychiatry & Human Behavior, School of Medicine at the University of California, Irvine. “But there is limited data on the beneficial effects of sleep apnea treatment on risk for dementia.”

He continued: “This study offers proof of concept evidence that treating sleep apnea may reduce Alzheimer’s disease risk. [It] also offers potential novel molecular targets for future study for those where positive airway pressure treatment is not feasible.” 

Coulson also noted that the findings support the need for further trials among human participants into the effects of intermittent oxygen deprivation and how these relate to dementia onset. 

What is sleep apnea?

This condition involves frequent and repeated pauses in breathing throughout the night, leading to highly disrupted sleep. Some individuals with sleep apnea wake up 100 times every hour.

When oxygen levels drop with each pause, “sleep goes from a deeper to a lighter stage,” shared Matta. And “there’s an abrupt wakefulness when the patient’s sleep cycle shifts to the lighter stage of sleep.”

Matta noted that this pattern also leads to increased blood pressure along with sympathetic stimulation — aka the triggering of the body’s ‘fight or flight’ mode. 

There are three types of sleep apnea: obstructive, central, and complex. However, obstructive and central sleep apnea are the most common.

“Obstructive sleep apnea is where recurrent partial or complete obstructions of the upper airway during sleep occur, leading to intermittent hypoxia and/or sleep fragmentation,” Nicola revealed.

This type is the one more often associated with dementia.

Meanwhile, she continued, central sleep apnea occurs because the brain intermittently stops sending signals for us to breathe. 

If you have an occasional bad night’s sleep, don’t panic. It’s believed that frequency is key to increased risk.

“Ongoing nights of sleep deprivation that become chronic are what leads to neurodegeneration over time,” explained Nicola. 

If you experience the following symptoms, Singh recommended getting assessed by a healthcare professional for sleep apnea:

  • Poor nighttime quality of sleep
  • Waking up multiple times at night
  • Going to the bathroom more than usual every night
  • Waking up tired and sleepy
  • Dry mouth
  • Morning headaches
  • Difficulty concentrating

How sleep apnea can be treated

While there’s currently no cure, “sleep apnea is highly treatable, and there are many potential treatments available,” assured Mander.

These include: 

  • Using a Continuous Positive Airway Pressure (CPAP) machine
  • Tackling snoring
  • Sleeping on your side
  • Raising the ‘head’ section of the bed
  • Losing weight — as obesity increases pressure on the airway
  • Reducing alcohol and nicotine intake

“Provided it’s not too serious and caught early, many people can relieve themselves of sleep apnea if they train themselves to be nose breathers while they sleep,” Nicola added. 

Takeaway

Sleep apnea is a common disorder affecting up to 30% of US adults, and causes breathing to repeatedly stop and start throughout the night. 

Its prevalence increases with age, although other risk factors include obesity and smoking.

While the new findings highlighted how intermittent oxygen deprivation influences brain cell death, they also affirm the need for greater investigation into the area.

“[They] underline the importance of conducting large-scale clinical trials to examine the potential of positive airway pressure treatment to reduce Alzheimer’s disease risk in older adults with sleep apnea,” stated Mander.

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