Have you noticed problems with your memory lately-that it’s not as sharp as it used to be? Or have you been having trouble concentrating or making decisions? A growing body of research suggests that sleep-disordered breathing could be playing a role.
What is sleep-disordered breathing?
Sleep-disordered breathing is an umbrella term for a group of conditions that cause breathing abnormalities while a person is sleeping. During sleep, all the muscles in the body relax somewhat, including those in the upper airway (the nose, mouth, throat, and windpipe). These muscles keep open the passageway through which air and oxygen move into the lungs when you inhale and clear them of carbon dioxide when you exhale.
In people with obstructive sleep apnea-the most common type of sleep-disordered breathing-the muscles in the back of the throat relax too much, narrowing or completely blocking the airway. This reduces or totally blocks airflow. These episodes are brief, typically lasting no more than 10 to 30 seconds, but they briefly deprive the brain of oxygen. Loud snoring-one of the hallmarks of sleep apnea-occurs as the air tries to squeeze past the narrowed or blocked airway. Loud snoring is certainly annoying, but a far more serious consequence of the obstructed airway is hypoxia (the state of low oxygen levels in the bloodstream).
Fortunately, when oxygen levels get too low while we’re asleep, an internal “alarm” goes off and triggers the brain to wake up the body and breathe. The startled sleeper awakens briefly, typically with a choke or gasp, but quickly falls back to sleep. Initially, breathing is normal, but this cycle recurs hundreds of times throughout the night, depriving the person of needed sleep.
Evidence of a connection
A number of studies have demonstrated a relationship between sleep-disordered breathing and cognitive impairment, but others have not. Now an analysis that combined data from 14 studies involving more than 4.2 million adults provides perhaps the strongest evidence to date of a connection. The researchers, who reported their findings in 2017 in JAMA Neurology, set out to answer two questions: What are the effects of sleep-disordered breathing on the risk of cognitive impairment? And, what are the effects of sleep-disordered breathing on cognitive function?
Their analysis of the data showed that people with sleep-disordered breathing were 26 percent more likely than those who didn’t have the condition to experience cognitive decline. It also showed that executive function-the mental processes needed to perform activities such as planning, organizing, paying attention, and following instructions-was slightly worse in people with sleep-disordered breathing. Interestingly, this analysis did not show that disordered breathing during sleep affected memory.
Additional recent evidence supporting a link comes from a 2017 study in the Annals of the American Thoracic Society, which reports that people with the APOE4 gene variant (which is associated with an increased risk of AD) appear to be at greater risk of diminished cognition from sleep-disordered breathing than those without it.
These investigators analyzed data from 1,752 participants (average age 68) in the Multi-Ethnic Study of Atherosclerosis (MESA) who underwent an in-home sleep study. The participants also answered standardized questions about sleep and underwent a battery of tests to measure their cognition.
The authors’ review of the data showed that increased levels of hypoxemia or increased daytime sleepiness were associated with poorer attention and memory. Increased daytime sleepiness was also associated with slower cognitive processing speed. Sleep apnea plus self-reported sleepiness was associated with poorer attention and processing speed. All of these associations were strongest in people with the APOE4 gene variant.
A 2015 study in the journal Neurology found that heavy snoring and sleep apnea may speed up the rate of cognitive decline in older adults. For this study, researchers reviewed the medical histories of 2,470 people, ages 55 to 90, who were participating in the Alzheimer’s Disease Neuroimaging Initiative. Participants had no memory or thinking problems or early-stage mild cognitive impairment or probable Alzheimer’s disease.
Overall, people with sleep-disordered breathing were diagnosed with mild cognitive impairment 10 years earlier, on average, than those who did not have sleep-breathing problems. When the researchers looked solely at people who developed mild cognitive impairment during the study, they found that those with untreated sleep-disordered breathing showed signs of cognitive deterioration at an average age of 77, compared with age 90 for those without difficulty breathing while asleep. The onset of Alzheimer’s also occurred at a younger age in those with sleep-disordered breathing than in participants without sleep troubles: 83 and 88 years, respectively.
It is important to note that none of these studies proves that sleep-disordered breathing causes cognitive decline, but they do provide additional supportive evidence that it may worsen the problem or hasten its onset.
How sleep apnea is diagnosed
Although sleep apnea may go undetected for years, it is easily documented by a sleep study conducted in a laboratory or at home with a portable monitoring device. These studies, which are performed overnight while you’re asleep, monitor various clinical signs, including airflow and breathing patterns, blood oxygen levels, and number of arousals from sleep per hour. (At-home monitoring devices are recommended only when the doctor suspects you have moderate or severe sleep apnea and you have no other illnesses or sleep disorders that might affect the results.)
Sleep apnea is diagnosed if testing reveals that you experienced five or more arousals per hour of sleep. Mild sleep apnea is defined as five to 14 arousals, 15 to 29 is moderate, and 30 or more is severe. If you have moderate or severe sleep apnea, your doctor is likely to recommend continuous positive airway pressure (CPAP) therapy. CPAP is administered using a device that consists of a nasal or facial mask that’s connected by a tube to a small machine. The machine delivers a steady stream of air through the mask into the throat. The resulting pressure keeps the airways open. If you’re overweight or obese, shedding pounds may also help.
Does treating sleep apnea help cognitive complaints?
More research is needed to answer this question. Of the three studies discussed above, only the authors of the Neurology article looked at the effect of treatment. They found that people who treated their sleep-breathing problems with a CPAP device were diagnosed with MCI about 10 years later than people whose problems were not treated; at age 82, on average, instead of age 72. Although it is not clear why, there was no association between CPAP use and delay in age of AD onset.
The bottom line
Even if treatment of sleep apnea is never conclusively shown to help with memory and cognition, there are other reasons why the condition shouldn’t be ignored. Notably, studies have shown that people with severe obstructive sleep apnea have double the risk of being involved in a motor vehicle accident when compared with individuals who don’t have it. Also, people with untreated obstructive sleep apnea are at increased risk for cardiovascular problems, including high blood pressure, heart attack, and stroke.
But the news isn’t all bad: Strong evidence shows that using the CPAP device regularly reduces the frequency of sleep apnea, decreases daytime sleepiness, lowers the risk of motor vehicle accidents, and improves blood pressure. What’s more, people who use their CPAP device regularly typically report feeling better, too.