Sleep apnea linked with Alzheimer's risk: Study

Researchers have revealed a connection between sleep apnea -- a disorder in which breathing stops and starts repeatedly -- and increased levels of a toxic brain protein commonly associated with Alzheimer's disease.

According to the researchers at Mayo Clinic in the US, people who are witnessed by a bed partner to have stopped breathing during sleep may have higher accumulations of an Alzheimer's disease biomarker called tau in a brain area that helps with memory.

Obstructive sleep apnea is a condition that involves frequent events of stopped breathing during sleep, although an apnea may also be a single event of paused breathing during sleep.

Tau, a protein that forms into tangles, is found in the brains of people with Alzheimer's disease.

"A person normally has fewer than five episodes of apnea per hour during sleep," said Diego Z Carvalho from the Mayo Clinic.

"Bed partners are more likely to notice these episodes when people stop breathing several times per hour during sleep, raising concern for obstructive sleep apnea," Carvalho said in a statement.

"Recent research has linked sleep apnea to an increased risk of dementia, so our study sought to investigate whether witnessed apneas during sleep may be linked to tau protein deposition in the brain," he said.

The study involved 288 people aged 65 and older who did not have cognitive impairment. Bed partners were asked whether they had witnessed episodes of stopped breathing during sleep.

Participants had positron emission tomography (PET) brain scans to look for accumulation of tau tangles in the entorhinal cortex area of the brain, an area of the brain in the temporal lobe that is more likely to accumulate tau than some other areas.

This area of the brain helps manage memory, navigation and perception of time.

Researchers identified 43 participants, 15 per cent of the study group, whose bed partners witnessed apneas when they were sleeping.

They found those who had apneas had on average 4.5 per cent higher levels of tau in the entorhinal cortex than those who did not have apneas, after controlling for several other factors that could affect levels of tau in the brain, such as age, sex, education, and cardiovascular risk factors.

"Our research results raise the possibility that sleep apnea affects tau accumulation," said Carvalho.

"But it is also possible that higher levels of tau in other regions may predispose a person to sleep apnea, so longer studies are now needed to solve this chicken and egg problem," he said.