University of California, Irvine researchers have identified a potential link between obstructive sleep apnea during REM sleep and early brain changes linked to cognitive decline. The study suggests that hypoxemia, or low oxygen levels during REM sleep, may damage brain regions crucial for memory in older adults without cognitive impairment.
Obstructive sleep apnea occurs when throat muscles relax during sleep, blocking the airway and causing frequent awakenings. This can lower oxygen levels and potentially harm small blood vessels in the brain. While the study does not establish causation, it highlights an association between sleep apnea and cerebral degeneration.
Published in Neurology, the research is part of the Biomarker Exploration in Aging, Cognition and Neurodegeneration study. It focuses on white matter hyperintensities—cerebrovascular damage visible via MRI—and structural changes in the medial temporal lobe essential for memory formation.
“Sleep apnea is important because low oxygen levels during sleep can harm the ability of our brain and bodies to function properly,” said Bryce A. Mander, assistant professor at UC Irvine. “Our study found that low oxygen levels from obstructive sleep apnea may be linked to cognitive decline due to damage to the small blood vessels in the brain.”
Michael Yassa, co-corresponding author and director of UC Irvine’s Center for the Neurobiology of Learning & Memory, noted: “Low oxygen during REM sleep seems to harm tiny blood vessels in the brain…This might help explain why even mild sleep apnea can impact brain health long before memory problems show up.”
The study involved 37 participants with an average age of 73 who did not have cognitive impairment; 24 had obstructive sleep apnea. Researchers found that lower oxygen levels during REM were strongly linked to increased white matter hyperintensities in frontal and parietal lobes—areas active during REM and vulnerable to low oxygen.
Vascular damage was also associated with thinning in the entorhinal cortex—a region often affected early by Alzheimer’s disease. Participants with thinner cortices showed poorer overnight memory retention.
“REM sleep is when your brain does some of its most important cleanup and memory storage work,” said Destiny E. Berisha from UC Irvine. “If oxygen levels drop during that time, we may be interrupting critical maintenance for the brain’s memory systems.”
The findings question current diagnostic practices for obstructive sleep apnea based on mild apnea-hypopnea index scores. Even those with mild scores experienced significant drops in REM-related oxygen levels linked to brain changes.
“This is important because we often rely on this [index] to determine treatment,” Mander stated.
The research supports evidence linking sleep disorders with dementia risk as untreated apnea could increase Alzheimer’s risk over time. More extensive studies are needed across diverse populations with more severe forms of obstructive apnea.
“Most research on sleep apnea is focused on non-REM-dominated parts of night,” Yassa remarked. “Our data suggest we may need closer attention on what happens during REM.”
Funded by grants from National Institute on Aging and American Academy Sleep Medicine Foundation; authors thank Biomarker Exploration participants for contributions.
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