Sleep apnea impact may affect cognitive function

NATION — A new study links sleep apnea to changes in key brain regions related to memory. Researchers estimate that about 936 million adults globally have sleep apnea—a condition where a person stops breathing when asleep, disrupting their rest.
Past studies show that sleep apnea can increase a person’s risk for several conditions, including obesity, type 2 diabetes, high blood pressure, and neurological diseases such as Alzheimer’s disease and other types of dementia.
“Sleep apnea is still an under-recognized and undertreated sleep disorder that can affect brain and cardiovascular health,” said Alberto R. Ramos, MD, MS, FAAN, FAASM, professor of clinical neurology and research director of the Sleep Medicine Program in the Miller School of Medicine at the University of Miami, fellow of the American Academy of Neurology. “Of importance, if sleep apnea affects brain health and increases the risk for dementias, then treatment of it can serve as a strategy to improve brain health and prevent these disorders, which are on the rise.”
Ramos is the lead author of a new study involving older adults of Latin descent that found people with sleep apnea may have an enlarged hippocampus, the area of the brain responsible for memory and learning. Additionally, researchers report that individuals with lower oxygen levels during sleep experienced alterations to the white matter of the brain. Although white matter normally decreases as we age, these changes may influence the progression of different brain disorders, including Alzheimer’s disease.
The study was recently published in Neurology, the medical journal of the American Academy of Neurology.
Why study sleep apnea and brain health in Latino
populations?
For this study, researchers recruited about 2,600 Latino individuals with an average age of 68.
“Latinos have an increased risk of Alzheimer’s disease compared to other ethnic groups, not fully explained by the known risk factors,” Ramos explained. “They also have an increased prevalence of sleep apnea, hence evaluating markers of brain health serves as a way to understand early markers of disease risk for Alzheimer’s disease and overall brain health in this population that seems to have a large burden of disease.”
At the start of the study, all participants were given a sleep test to take home that measured how many apneas—or breathing stops—they had while sleeping. The test also measured incidents of hypopneas, or shallow breathing, during sleep, and researchers measured the amount of oxygen in their blood.
Following the sleep test, participants were divided into three groups:
Those who had fewer than five sleep disruptions per hour or no sleeping issues
Those with five to 15 disruptions and mild sleeping problems
Those with more than 15 disruptions and moderate to severe sleeping difficulties
Sleep issues linked to increased brain volume
Researchers followed up with study participants after 10 years. All participants received brain scans to measure their brain volume and any areas where their white matter may have been damaged.
Upon analysis, Ramos and his team found that participants with the most sleeping issues had 0.24 cubic centimeters (cm³) greater brain volume in the hippocampus compared to those with no sleeping problems. Additionally, researchers discovered that for every additional sleep disruption, there was a 0.006 cm³ brain volume increase in the hippocampus.
“We think, in this specific case of sleep apnea, that increased size means increased swelling, because of inflammation or overall damage,” Ramos explained.
Lower sleep oxygen levels linked to more white matter damage
When examining blood oxygen levels, scientists found that lower oxygen levels during sleep were correlated with both higher hippocampal volume and white matter hyperintensities—areas of brain damage.
“We think that the increase in white matter hyperintensities tells us that there is vascular brain disease in people with sleep apnea, and this is in part explained by the low oxygen levels that you see in this disease—more so in some cases than others,” Ramos said. “These findings, while still needing to be replicated, can lead to treatment studies and targets for interventions.”
“Dementias still don’t have a cure, and many of the brain changes that lead to dementia start decades before clinical symptoms develop,” he continued. “Hence our study allows us to determine the role sleep apnea may play in the process that leads to dementia and what are some of its early markers and pathways, such as vascular brain disease.”
“The diagnosis of sleep apnea, and hopefully the treatment of it—we still need treatment studies to confirm this—should be part of the overall strategy to maintain proper brain health,” Ramos added.
Can treating sleeping problems reduce dementia symptoms?
David Merrill, MD, PhD, a board-certified geriatric psychiatrist at Providence Saint John’s Health Center in Santa Monica, CA, and Singleton Endowed Chair in Integrative Brain Health, spoke about this study.
“Sleep is a factor that can either be protective or risky for cognitive health,” Merrill, who was not involved in this research, explained. “The effects of sleep on cognitive health depend on the attributes of an individual’s sleep, including the quality, quantity, frequency, and even the regularity of sleep. With high-quality, restorative sleep, the brain’s function is enhanced and protected as we age. If sleep is chronically disrupted, this can lead to a number of health issues including headaches, fatigue, and memory loss that worsens over time.”
“The disrupted, poor-quality sleep seen in sleep disorders leads to both acute and chronically worsening changes in the brain,” he continued. “Normally, a good night’s sleep literally allows for repair and restoration of brain function to the levels seen at the beginning of the prior day. We now know through research that the brain has a specialized cleaning system, called the glymphatic system, that is most active during the deepest stages of sleep. Similar in function to the lymphatic system found in the rest of our body, the glymphatic system drains away waste products produced during normal daily metabolism,” said Merrill.
According to him, “Dementia continues to be a disorder without a cure, and the available drug therapies are marginally effective at treating its symptoms, so it’s crucial to use all available strategies to treat sleep symptoms to alleviate dementia symptoms.”
“That includes all the intuitive, but often difficult to achieve, elements of sleep hygiene,” he noted.
— Corrie Pelc