Sleep—and Hearing—Interrupted What could account for a link researchers have found between hearing loss and sleep apnea? Both biological and psychological factors could be at play. Features
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Features  |   February 01, 2018
Sleep—and Hearing—Interrupted
Author Notes
  • Nancy Volkers is a freelance medical writer based in Vermont. nvolkers@nasw.org
    Nancy Volkers is a freelance medical writer based in Vermont. nvolkers@nasw.org×
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Hearing Disorders / Features
Features   |   February 01, 2018
Sleep—and Hearing—Interrupted
The ASHA Leader, February 2018, Vol. 23, 56-63. doi:10.1044/leader.FTR2.23022018.56
The ASHA Leader, February 2018, Vol. 23, 56-63. doi:10.1044/leader.FTR2.23022018.56
It happens in the dead of night, often without people knowing it. Their airway gets blocked as they sleep.
They try to breathe, but little or no air gets through. Blood oxygen drops so low that the brain jolts them awake. They may gasp or make choking sounds as they start breathing again.
This can happen 1 to 100 times an hour, according to the National Heart, Lung, and Blood Institute. It can destroy sleep quality, affecting daytime functioning as well as long-term health.
It’s called obstructive sleep apnea. And it affects more than 18 million adults, according to the National Sleep Foundation. While it’s most commonly known for causing snoring and daytime sleepiness and being associated with heart attack, stroke and diabetes, some recent research suggests that sleep apnea may also put people at risk for hearing loss.
Using data from the Hispanic Community Health Study/Study of Latinos, researchers at Albany Medical College found a 30-percent increased risk for hearing loss among those with sleep apnea. “This is the largest study to show a strong association between hearing impairment and sleep apnea,” says Amit Chopra, lead author of the study and assistant professor in the Albany Medical College Division of Pulmonary and Critical Care Medicine. The research was published in the May 2016 issue of the Journal of Sleep Medicine.
The study included data on 13,967 adults—33 percent of whom had a hearing impairment, and 10 percent of whom reported sleep apnea. Among those with a hearing issue, 11.1 percent had sleep apnea. In those with normal hearing, 8.7 percent reported apnea. (Snoring also was more common among people with sleep apnea, but was not associated with hearing loss.)
What could account for this interplay between apnea and hearing loss? Researchers aren’t sure if there’s a biological association, but some studies point to a possible link between low oxygenation and hearing loss. Others note the associations among the two conditions and metabolic risk factors such as obesity, high blood pressure and type 2 diabetes. There’s also a possibility that apnea treatment could help tinnitus.

Researchers at Albany Medical College found a 30 percent increased risk for hearing loss among those with sleep apnea. Lowered oxygen levels may, over time, damage cochlear cells.

Apnea facts
An obstructive sleep apnea diagnosis requires at least five episodes of disordered breathing in an hour. Patients with at least 15 episodes per hour have moderate apnea; those with 30 or more episodes per hour have severe apnea.
Daytime symptoms include sleepiness and fatigue. It’s difficult to focus, and a person’s mood may suffer. They may choke or gasp during sleep. Snoring can occur, but is not a necessary sign of apnea. The gold standard for diagnosis is a sleep study in which the person stays overnight in a clinic, monitored with polysomnography.
Typical treatment involves using a CPAP (continuous positive airway pressure) machine, which keeps the airway open. Patients wear a facemask connected to a pump. Treating clinicians may also recommend that patients lose weight if excess weight contributes to the apnea. Another option is surgery to remove excess tissue from the pharynx and soft palate. But surgery is typically considered only after other treatments have failed.
Mechanisms
Whether there’s a biological association between apnea and hearing loss remains an open question. Chopra and others suggest that lowered oxygen levels can, over time, damage cochlear cells. He notes that hypoxia may have a marked effect at the apex of the cochlea, which is oxygenated by a relatively sparse collection of blood vessels. Low-frequency sound waves are conducted there.
Though the incidence of low-frequency hearing loss was low in the Hispanic Community Health Study, the analysis showed a strong association with sleep apnea: Those with the condition had more than double the risk for low-frequency hearing loss.
Some research supports the idea that lowered oxygen levels are a potential culprit.
In 2016, researchers from South Korea published a study of 41 patients with severe obstructive sleep apnea. Each participant completed a sleep study and had their oxygen saturation levels measured throughout the night. When the researchers compared each patient’s lowest measurement of the night, those with the smallest numbers were at greatest risk of hearing impairment.
Other studies have suggested that the lack of oxygen may impair transmission of nerve impulses. A study of 38 adult males—published in 2016 in the Brazilian Journal of Otorhinolaryngology, —found that those with sleep apnea had altered responses on an ABR test. However, more severe apnea was not linked with worse response.
If apnea does play a role in hearing loss, could prompt treatment reduce the risk? There’s little research to suggest that. Chopra is considering a prospective study on the effects of CPAP treatment on hearing loss, but says the idea is “very preliminary.”
Risk factor complexity
Sleep apnea interacts with many other health-related issues, which makes its effects difficult to isolate. Risk factors for apnea include obesity, high blood pressure, type 2 diabetes, congestive heart failure, history of stroke and arrhythmia. However, people who already have sleep apnea also are at higher risk for all of these conditions.
Studies have helped researchers to form hypotheses about a biological mechanism, but the question is still open, says Charles E. Bishop, associate professor and audiologist in the Department of Otolaryngology and Communicative Sciences at the University of Mississippi Medical Center, Jackson. “Certain cells form fatty droplets—it could be increased fat buildup in the cochlea,” he suggests. “There could be blood clot issues or microvascular disease.”
Bishop is an NIH coinvestigator on the Jackson Heart Study, the largest single-site longitudinal investigation of cardiovascular disease among African Americans. He and colleagues recently found an association between stroke risk and hearing loss in study participants, with higher risk predicting greater loss. In 2016, Jackson Heart Study data analyses (published in Laryngoscope) showed that increased levels of physical activity were associated with better hearing.
“I would look at sleep apnea as a component of cardiometabolic risk: a collection of factors that can lead to cardiovascular disease,” says Bishop. “If you look at any relationship between these factors and hearing, it’ll be positive, because people have this factor, and this one, and this one. And what’s important is that carrying these risk factors for a long period of time can result in systemic problems, including auditory ones.”
How long is a “long period of time”? Researchers don’t really know. As of yet, there are no longitudinal studies that could shed light on the answers. From a public health perspective, however, patients can benefit from increased awareness of all cardiometabolic risk factors, including sleep apnea, and a focus on minimizing them with exercise, healthy food choices and other treatment where necessary.
Obesity—one of the major risk factors for sleep apnea—has risen dramatically for the past six decades. More than a third of adults and 17 percent of children are obese, according to data from the U.S. Centers for Disease Control and Prevention.
Though childhood obesity rates have slowed in recent years, more than 12 million American children are obese. More than half of them will carry their obesity into adulthood. As they age, this trend will likely affect population-level health—including effects on hearing.
“I think these kids will have hearing impairments [in adulthood],” said Bishop. “We can’t quantify that, because how much would it cost to follow thousands of 12-year-olds for decades? But as society gets more obese and more sedentary, we’re probably going to be seeing more people with hearing problems.”
As in adults, obesity is a risk factor for childhood sleep apnea, which affects as many as 60 percent of obese children (see sidebar below).

“Carrying [metabolic] risk factors for a long period of time can result in systemic problems, including auditory ones.”

Perception is reality
Another of sleep apnea’s effects lies in the realm of perception, says Bishop.
“Apnea can exacerbate how people feel about their hearing problem,” he notes. “If you’re not getting good sleep, you’re less tolerant of everything. Someone in good physical shape may not even perceive that they have a hearing loss, whereas someone with a lot of health problems will perceive it and feel worse about it.”
Bishop sees this phenomenon in many patients who have both apnea and tinnitus. “It’s not so much that they have worse tinnitus [than other patients], but they’re more annoyed by it,” he says. In his experience, “Most people who have tinnitus don’t seek treatment for it. But most who do seek treatment have apnea.”
A recent study in the journal Laryngoscope did find an association between apnea and tinnitus. It included data from more than 130,000 Taiwanese adults. About 22,000 had been diagnosed with tinnitus. The study found that those with sleep apnea had a 36-percent increased risk of having tinnitus, compared with those who did not have apnea.
Shedding light on this pattern is research by Fatima Husain, an associate professor in the Department of Speech and Hearing Science at the University of Illinois, Urbana-Champaign. People who complain of bothersome tinnitus have different responses to unpleasant sounds than other people do, she and colleagues found in a functional MRI study published in 2015 in PLoS One.
In response to unpleasant sounds, people with bothersome tinnitus show activity in the amygdala, the emotional center of the brain. In contrast, people with mild or no tinnitus show activity in the frontal cortex, where problem-solving and judgment occur. “They are thinking it through logically, telling themselves that this is an unpleasant sound but I don’t have to be bothered by it,” Husain says. “They control their emotions more.”
Husain notes that people with bothersome tinnitus also tend to have more trouble falling asleep and staying asleep. To see what was going on in the brain during a resting state, Husain and colleagues measured the brain activity of people with tinnitus while they lay in the MRI machine. “We ask patients to just lie there and not think of anything in particular,” she says. “To my knowledge there’ve been no studies of people actually sleeping in the MRI, but this is the closest we’ve gotten.”
The results, published in NeuroImage:Clinical in August 2017, showed that in people with tinnitus, the brain did not relax. “If you have even mild tinnitus, the attention network in the brain is more engaged … and the resting state network is not being used as much,” Husain says. “Some part of your brain is always paying attention to this internal sound. That’s exhausting.”
Husain recommends using white-noise machines or soothing CDs (set on repeat) to help the brain stop focusing on the tinnitus and allow for more and better sleep.

“It’s not so much that [patients with sleep apnea] have worse tinnitus, but they’re more annoyed by it.”

Breaking the cycle
For patients with apnea and tinnitus, treatment of the former often also helps the latter. Bishop recalls seeing a referred patient who had hearing loss and tinnitus. Her hearing loss was minor, but her tinnitus was aggravating her.
“I was trying to talk to her about what tinnitus is, and she fell asleep,” Bishop says. “I sent her for a sleep study and it was the worst case of apnea that the doctor had ever seen.”
One year later, the patient returned, compliant with CPAP treatment. “Now she’s alert and focused,” he recalls. “But when I started talking to her about her tinnitus she said, ‘Oh, no—that’s not a problem anymore.’”
“People who have apnea see the world through foggy glasses,” says Bishop. “It’s one of the most critical health problems today. And its relationship to how someone feels about their hearing loss may matter more than whether it’s clinically related to hearing loss.”
When Apnea and Hearing Loss Intersect in Kids

In children, the most common cause of obstructive sleep apnea is enlarged tonsils and adenoids. However, as in adults, obesity is a risk factor: As many as 60 percent of obese children experience sleep apnea.

Beyond those two risk factors, other children with both apnea and hearing loss generally have an underlying health condition, says Sumit Bhargava, clinical associate professor of pediatrics-pulmonary medicine at Stanford University School of Medicine.

“Where sleep apnea and hearing loss intersect in children is in genetic syndromes that lend themselves to both,” Bhargava says. “If a child has multiple medical problems and hearing has not been checked, it would be wise to consider an evaluation. It’s also important if children are having issues with school and behavior. School-based hearing screenings don’t always pick up issues.”

Bhargava sees many children who are falling asleep in school or having behavioral issues. “The behavioral issues might certainly be due to a sleep disturbance,” he says. “Sometimes, you discover hearing loss during the assessment. It’s reasonable for both things to be considered.”

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February 2018
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