People with obstructive sleep apnea who spend less time in deep sleep may be more likely to develop brain biomarkers associated with an increased risk of stroke, Alzheimer’s disease and cognitive decline, according to new research published May 10, 2023 online. issue Neurology®Medical Journal of the American Academy of Neurology. The study did not prove that these sleep disorders cause changes in the brain or vice versa. It only shows a link.
The study looked at sleep factors and biomarkers of white matter health in the brain. Biomarkers measure how well the brain’s white matter is preserved, which is important for connecting different parts of the brain. One biomarker, white matter hyperdensity, are small lesions that appear on brain scans. White matter hyperdensity becomes more common with age or with uncontrolled high blood pressure. Another biomarker measures the integrity of the axons that make up the nerve fibers that connect neurons.
These biomarkers are sensitive markers of early cerebral vascular disease. Finding severe sleep apnea and reduced slow-wave sleep associated with these biomarkers is important because there is no cure for these changes in the brain, so we need to find ways to prevent them from happening or getting worse.”
Diego Z. Carvalho, MD, MA, study author, Mayo Clinic in Rochester, Minnesota, and a member of the American Academy of Neurology
The study involved 140 people with obstructive sleep apnea with an average age of 73 who underwent a brain scan and also a nighttime study in a sleep lab. The participants did not have cognitive problems at the beginning of the study and did not develop dementia by the end of the study. A total of 34% had mild cases, 32% had moderate, and 34% had severe sleep apnea.
The sleep study examined how long people stayed in slow-wave sleep, which is also called stage three non-rapid wave sleep, or deep sleep, and is considered one of the best indicators of sleep quality. The researchers found that for every 10-point decrease in the percentage of slow-wave sleep, there was an increase in the amount of white matter hyperintensity similar to the effect of being 2.3 years older. The same decrease was also associated with decreased axonal integrity similar to the effect of being three years older.
People with severe sleep apnea have a higher volume of white matter hyperintensity than do people with mild or moderate sleep apnea. They also reduced the integrity of the axon in the brain.
The researchers took into account age, gender, and conditions that can influence the risk of brain changes, such as high blood pressure and high cholesterol.
“More research is needed to determine whether sleep problems affect biomarkers in the brain or vice versa,” Carvalho said. “We also need to consider whether strategies to improve sleep quality or treat sleep apnea can influence the course of these biomarkers.”
The split-night design of the sleep study limited this comprehensive study. Participants’ sleep was observed and their sleep factors measured until they met criteria for a diagnosis of obstructive sleep apnea, often in the first two to three hours of sleep. Then they received a positive airway pressure machine for the rest of the night. So sleep measurements may not be representative of a full night’s sleep.
The study was supported by the National Institutes of Health, the Gerald and Henrietta Rauenhorst Foundation, the Mellis Family, the Alexander Family Alzheimer’s Research Professorship, the Mayo Foundation, the Alzheimer’s Association, the Liston Award, the Elsie and Marvin Dekelbaum Family Foundation, and the Schuler Foundation.