Sleep apnea, less deep sleep tied to worse brain health

People with sleep apnea who spend less time in deep sleep may be more likely to have brain biomarkers that have been associated with an increased risk of stroke, Alzheimer’s disease and cognitive decline, according to a new study. Although the observational study can’t prove cause and effect, it’s one more reason to get sleep apnea treated while scientists see what else they might do to mitigate the risks.

The investigators analyzed data from 140 participants in the Mayo Clinic Study of Aging (mean age, 72.7; about 60%, men) who underwent at least one magnetic resonance imaging (MRI) scan and polysomnography (PSG) – that is, 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 MRIs revealed two cerebrovascular disease (CVD) biomarkers associated with the integrity of the brain’s white matter, of which white matter hyperintensities are particularly important. White matter hyperintensities, are tiny lesions in the brain that become more common with age or with uncontrolled high blood pressure.

The PSG examined how long people spent in slow-wave sleep – also called non-REM stage 3, or deep sleep – which is considered a reliable measure 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. That decrease also was associated with reduced axonal integrity similar to the effect of being three years older.

After adjustment for age, sex and conditions such as high blood pressure and high cholesterol, people with severe sleep apnea had a higher volume of white matter hyperintensities than those with mild or moderate sleep apnea, as well as reduced axonal integrity.

“More research is needed to determine whether sleep issues affect these brain biomarkers or vice versa,” study author Diego Z. Carvalho, MD, MS, of the Mayo Clinic in Rochester, Minnesota,. “We also need to look at whether strategies to improve sleep quality or treatment of sleep apnea can affect the trajectory of these biomarkers.”