Obstructive sleep apnea, a common sleep disorder in older adults, is associated with changes in brain structure seen in early dementia, according to a study published online in the peer-reviewed European Respiratory Journal.
In sleep apnea, the airways become partially or repeatedly blocked when the soft tissue in the back of throat relaxes during sleep. In the United States, more than 18 million adults, especially older adults, experience the condition, whose symptoms include excessive snoring and daytime sleepiness.
In a 2017 study published in the American Journal of Respiratory and Critical Care Medicine, sleep apnea severity was associated with cortical thickness and an increase in gray matter volume in the brains of middle-aged and older adults. However, it's unclear whether increased gray matter volume leads to atrophy or is associated with cognitive decline.
To examine the association between sleep apnea and its effect on the brain and cognitive abilities, researchers at the University of Sydney recruited 83 adults between the ages of 51 and 83, who were defined as at-risk for dementia because they sought help for memory or mood problems, and had no prior diagnosis of sleep apnea.
Participants were examined and their medical history and medication use were documented. In addition, their psychiatric and neurologic history was assessed via a standardized interview. They also reported their depressive symptoms using a standard depression scale.
Within four weeks of their examination and assessment, each participant had an MRI scan to measure the thickness of various regions of the brain cortex, including the area involved in hearing, speech, and memory. Using polysomnography—a technique that records brain activity, levels of oxygen in the blood, heart rate, breathing, and movements—a sleep specialist monitored participants’ sleep at a clinic. Measuring oxygen levels, which are known to be reduced in sleep apnea, helped researchers determine whether participants had the condition.
Participants who had low levels of oxygen in their blood during sleep were more likely to have reduced thickness in the left and right temporal lobes of the brain, regions that are important in memory and implicated in dementia. The same participants demonstrated a decreased ability to learn new information after being administered a test that measures memory and recall.
Conversely, participants with indications of sleep apnea were more likely to have an increase in thickness in other regions of the brain, which could be signs of swelling and inflammation in response to lower levels of oxygen, the researchers reported.
"These changes in gray matter reveal how sleep apnea might contribute to neurodegenerative processes in older adults," the researchers wrote. They did note, however, that their findings do not prove that sleep apnea is a risk factor for dementia. Further research with larger samples is needed to determine whether sleep apnea is a truly modifiable risk factor for dementia.