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Untreated sleep problems may contribute to cognitive decline. FG Trade/Getty Images
  • A study finds that obstructive sleep apnea can result in a loss of cognitive function.
  • The research is unique in that its participants were all healthy, without comorbidities often suggested as the mechanisms behind sleep apnea’s connection to cognition.
  • The study indicates that loss of cognitive function from obstructive sleep apnea can occur as early as middle age in men.

With obstructive sleep apnea (OSA), a person’s airway intermittently becomes blocked for 10 seconds or more during sleep. These breathing interruptions are linked to an eventual reduction in cognitive function, and it has been hypothesized that this is due to cardiovascular or metabolic comorbidities.

A new study of people without such comorbidities finds that sleep apnea itself can result in premature cognitive decline as early as middle age.

A unique group of men participated in the study. OSA is usually diagnosed in people who also have systemic hypertension, hyperlipidemia, diabetes, cardiovascular, and other metabolic diseases.

That none of the study’s participants had any such comorbidities means that this investigation is the first to explore the cognitive effects of OSA in otherwise healthy and non-obese people.

The researchers found that OSA was linked to poorer executive function, visuospatial memory, vigilance (sustained attention), psychomotor function, and impulse control in its otherwise healthy participants.

The study is published in Frontiers in Sleep.

A previous analysis of data from 16 countries concluded that 936 million adult men and women from 30 to 69 years of age have mild-to-severe OSA, with 425 million having moderate-to-severe OSA. In the United States, it is estimated that 25 million people have the condition.

There are two types of sleep apnea. With the less-common central sleep apnea, the brain fails to consistently signal the muscles that control breathing.

OSA is more common.

With obstructive sleep apnea, dilator muscles that normally keep the soft palate at the back of the throat open during breathing fail to do so, or allow the tongue to block the airway. Breathing is interrupted until the person with the condition — often without fully waking up — gasps or snorts to re-open the airway, and resumes breathing.

In the study, researchers recruited 27 men who had been recently diagnosed with OSA. They ranged in age from 35 to 70, with an average age of 42.6 years. Seven matched individuals without OSA served as a control group for comparison.

After a series of observations and measurements to assess individuals’ conditions, the researchers compared their cognitive function to individuals in the control group. To do so, they administered the Cambridge neuropsychological test automated battery, a “highly sensitive, validated touchscreen-based cognitive assessment” to examine 11 cognitive domains.

Lead author, neuroscientist Dr. Ivana Rosenzweig, clinical reader in the Neuroscience of Sleep at King’s College London, U.K., recalled:

“Our team, together with our international collaborators, has worked on this study for several years, which is much longer than we initially envisaged.”

Dr. Rosenzweig credited the study’s unique cohort to first author Dr. Valentina Gnoni, a former Ph.D. candidate at King’s College London, “whose passion for sleep research and for her patients meant that, through her hard work, we were eventually able to recruit this cohort of very special and rare patients.” She said her team worked with “simply wonderful” participants.

“Craniofacial and physiologic particularities can be a risk factor for OSA — having a short chin, large tonsils, a large tongue, etc.,” explained neuroscientist Dr. Nadia Gosselin, from the University of Montreal, Canada, who wasn’t involved in the study.

“These particularities put a person more at risk of upper-airway obstruction during sleep,” she said.

While it is not clear how OSA promotes cognitive decline, its basic attributes may be the culprits, including sleep interruption, intermittent hypoxemia, neuroinflammation, and oxidative stress.

Dr. Gosselin explained, “By fragmenting sleep chronically, OSA also prevents sleep from playing its role in memory consolidation, brain plasticity, and cerebral metabolic waste clearance.”

A couple of other possible mechanisms, she added, are systemic inflammation and blood-brain barrier dysfunction leading to neuronal death.

“One study has reported increased oxidative stress and inflammation specifically in the hippocampus and the entorhinal cortex, two brain regions that degenerate early in [Alzheimer’s disease],” said Dr. Gosselin.

There are clues that one may have OSA, said Dr. Rosenzweig. Often, a person’s bed partner will be the first to realize there is a problem. If someone has early morning headaches, is unusually sleepy throughout the day, or feels an increased need to get up and urinate during the night, they might have OSA.

For people concerned they may have the condition, Dr. Rosenzweig recommended home pulse oximetry testing. This can typically be arranged through one’s doctor, or at a sleep disorder clinic.

“Given these findings and increasingly recognized links of OSA with dementia, and a number of other serious diseases, one should not ignore signs that they may have it,” Dr. Rosenzweig said.

How to treat sleep apnea

The good news is that OSA can frequently be resolved with simple lifestyle changes, such as adopting a healthier diet, exercising more, and losing weight, she added.

Physicians can also help patients control OSA through a variety of therapeutic methods.

The most common OSA device is the CPAP machine, which exerts Continuous Positive Airway Pressure during sleep to keep the airway passage open. CPAP and other breathing-assistance machines, or medication, may also be prescribed for people with central sleep apnea.

Other treatments for OSA include dental appliances or oral mandibular advancement devices that keep the tongue from blocking the throat. There are also neurostimulation implants for OSA, and surgery is sometimes helpful.