Sleep apnea may be linked to certain indicators of poorer brain health, according to a new study.
The study, published Wednesday (May 10) in the journal Neurology (opens in a new tab)looked at people obstructively Sleep apnea (OSA), a condition in which the muscles in the upper part of the throat relax during sleep, blocking the airway. The researchers used magnetic resonance imaging (MRI) and sleep studies to examine whether sleep apnea and disturbed sleep were associated with two types of unusual patterns in the brain’s white matter: isolated wires extending from cells cerebral.
Both severe sleep apnea and reduced time spent in deep sleep stages were associated with these two biomarkers, which have previously been linked to an increased risk of developing Alzheimer’s disease or general cognitive impairment, as well as a stroke.
The researchers found “a fairly significant association between slow wave sleep duration or deep sleep time and these white matter measures,” he said. brycemander (opens in a new tab)assistant professor of psychiatry and human behavior at the University of California, Irvine, who was not involved in the study.
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The study included 140 people with OSA whose average age was about 73 years. All participants were tested for one of the two biomarkers, but only 103 were also tested for the second. The overall group was split relatively evenly between people with mild, moderate, and severe OSA, with most people having no cognitive decline during the study.
One of the biomarkers the researchers looked for in brain scans were white matter hyperintensities, “bright spots commonly seen in the brain’s white matter on MRI, which appear with aging and vascular disease.” Dr Diego Carvalho (opens in a new tab), assistant professor of neurology at the Mayo Clinic Center for Sleep Medicine and lead author of the study, wrote in an email to LiveScienceKick.com. “They represent areas of damage to the white matter.”
The second biomarker, called “corpus callosum fractional knee anisotropy,” is related to the way water flows through brain cell wires, or axons. Changes in this flow of water, Carvalho wrote, are related to axon damage and may be an early sign of vascular disease. The corpus callosum is a set of nerve fibers that connect the two hemispheres of the brain and contains the densest white matter of the organ.
Using polysomnography, that is, the variety of data collected during a sleep study, the researchers found that participants who spent less time in slow-wave sleep seemed more affected by both types of biomarkers on their MRIs. Separately, people with severe OSA also seemed more affected by white matter abnormalities than people with mild or moderate OSA.
The research reveals associations between sleep apnea, deep sleep, and white matter abnormalities, but cannot say whether these sleep differences caused the abnormalities or whether white matter differences might be interfering with sleep. It could also be that sleep and white matter abnormalities impact each other, Mander said, contributing to a vicious cycle of poor sleep quality and poorer brain health.
“To me, I think that’s the most likely outcome,” he said.
One limitation of the study is that polysomnography data was only collected during the first hours that participants slept; people’s sleep patterns could have been different later in the night. After their sleep study, anyone who met the criteria for sleep apnea received treatment in the form of a continuous positive airway pressure (CPAP) machine, which can help keep the airways open. Carvalho said data from this “treatment phase” were not included because differences in how people responded to CPAP would have clouded the data.
The MRIs and polysomnograms were taken, on average, about 1.7 years apart, but the researchers only collected each type of data at any given time, offering only snapshots of the patients’ brains and sleep patterns and not how they might change over time. The study also did not follow up the participants to see who might develop dementia.
Mander said future research should examine how sleep apnea’s impact on rapid eye movement (REM) sleep, the stage of sleep in which most dreams occur, might affect the brain. (Slow wave sleep occurs in certain stages of non-REM sleep). However, the new study introduces important insights about “how sleep apnea and sleep disorders might be associated with cognitive decline,” she said.