The study involved 140 people with obstructive sleep apnea with an average age of 73 who had a brain scan and also an overnight study in a sleep lab. The participants did not have cognitive issues at the start of the study and had not developed dementia by the end of the study. A total of 34% had mild, 32% had moderate and 34% had severe sleep apnea.
The sleep study examined how long people spent in slow-wave sleep, which is also called non-REM stage 3, or deep sleep, and is considered one of the best markers 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 hyperintensities similar to the effect of being 2.3 years older. The same decrease was also associated with reduced axonal integrity similar to the effect of being three years older.
People with severe sleep apnea had a higher volume of white matter hyperintensities than those with mild or moderate sleep apnea. They also had reduced axonal integrity in the brain.
The researchers accounted for age, sex and conditions that could affect risk of brain changes, such as high blood pressure and high cholesterol.
“More research is needed to determine whether sleep issues affect these brain biomarkers or vice versa,” Carvalho said. “We also need to look at whether strategies to improve sleep quality or treatment of sleep apnea can affect the trajectory of these biomarkers.”
The split-night design of the sleep study led to a limitation of this overall study. Participants’ sleep was observed and their sleep factors measured until they met criteria for the diagnosis of obstructive sleep apnea, mostly in the first two to three hours of sleep. Then they received a positive airway pressure machine for the rest of the night. So the sleep measurements may not be representative of a full night of sleep.