Sleep apnea linked to smaller brain volume, study finds

CNN

According to a recent study, a part of the brain that is connected to memory shrinks in people who have severe sleep disordered breathing. This can include heavy snoring or sleep apnea. Sleep apnea is a condition where people stop breathing for at least 10 seconds, multiple times per night.

It is becoming more widely accepted that this sleep disorder will increase dementia risk if left untreated. We present new evidence that focuses on the medial temporal lobe, an area of the brain affected early in Alzheimer's.

The medial temporal is a part of the brain that is essential for recalling facts and events and storing them in memory. The hippocampus is buried deep within that region. It's a complex structure important for learning, memory consolidation and encoding, as well as spatial navigation.

The study found that the loss of brain volume only occurs when there are signs of beta amyloid plaques. This is a hallmark of Alzheimer's.

Rauchs stated that 'we found that greater sleep apnea severity was associated with smaller volumes in the medial temporal and hippocampus'. The people without amyloid plaques had a lower brain volume even though they suffered from severe sleep apneas.

Experts say that amyloid buildup can begin decades before clinical signs of cognitive decline. It may even start in your 30s or 40s. According to a study published in February 2022, after age 70, a third of cognitively-normal people have amyloid deposits in their brain tissues. The deposits are not always associated with Alzheimer's. Many older people who have amyloid in the brain do not develop Alzheimer's.

Rudy Tanzi is a professor at Harvard Medical School, Boston, and he was not involved with the study. Tanzi said that during deep, slow-waved sleep the brain removes much of the buildup of amyloid in the brain.

Adults need seven uninterrupted hours of sleep to be able to achieve deep sleep and rejuvenate their brain. People who snore or have sleep apnea may experience hundreds of mini-arousals each night, even though they are unaware.

Tanzi wrote in an email that it was logical to associate sleep apnea with reduced brain volumes in older people, especially those with amyloid.

If the amyloid isn't properly removed, the Alzheimer's pathology will begin, ultimately leading to dementia. Tanzi is the director of genetics and ageing research at Massachusetts General Hospital, Boston.

Sleep apnea plus plaques

The study published in the journal Neurology on Wednesday examined data collected from 128 participants aged 65 and older who were participating in Age Well in Caen, France, a randomized clinical trial that is currently ongoing. The trial aims to test cognitive aging interventions.

At the beginning of the study, all participants were healthy and free from any chronic or cognitive diseases. The study excluded participants who had sleep apnea and those with sleep disordered breathing treated by continuous positive airway pressurization (CPAP).

The group was subjected to brain scans and memory tests, which were repeated after 21 months. They also underwent an overnight sleep study at home. Sleep tests revealed that 91 out of 122 participants in the study had moderate or severe sleep apnea. However, most did not have any obvious symptoms. Only 11 people reported excessive daytime fatigue.

26 of the participants showed amyloid deposits in their brain tissue. Severe sleep disordered breathing in these people was associated with less volume of the medial temporal region. The study found that the more severe the apnea was, the greater loss of volume.

Rauchs also noted that 'lower volume in certain regions of the medial temporal lobe was associated with poorer memory performance 18 months later'.

No shrinkage in the brains was observed for people with sleep apnea and no amyloid deposits. Rauchs stated that this finding indicates certain individuals are more susceptible to the negative effects of sleep disorders which impact breathing and disrupt sleep.

Rauchs noted that people in the early stages of Alzheimer's showed a particular vulnerability to sleep apneas. Further studies should examine whether treating sleep disordered breathing can improve cognition or prevent or delay neurodegeneration.

Sleep apnea affects the brain

Sleep apnea affects 936 millions adults between 30 and 69 years old. Many more are undiagnosed. According to research, if sleep apnea remains untreated and is severe, the chances of death from any cause are three times higher.

In a study published in May, researchers found that people with severe sleep disorders who spend less time in deep slow-wave sleep have more white matter damage in the brain than those who sleep more slowly-waved. The study found that for every 10% reduction in time spent in slow-wave, deep sleep, white matter hyperintensities in the brain increased. This is equivalent to 2.3 years of age.

A study published in July 2018 found that severe sleep apnea is associated with brain changes that are concerning for middle-aged adults and older adults. The study found that people with sleep apnea who have low oxygen levels in their blood are more likely to suffer from thinner brain tissue in certain areas linked to dementia.

Those people were less able to recall and remember new information when tested. They were also more likely to show thickening in other brain regions, which could indicate swelling or inflammation.

Rauchs stated that in an earlier study, she found the amyloid load in the brain was predicted by the severity associated with sleep apneas. In sleep apnea, hypoxia occurs when the brain is not getting enough oxygen.

We surmise that the hypoxia could also have a detrimental effect on the volume in the regions of the lateral temporal lobe. She said that some areas of the medial lobe, such as the hippocampus, are especially vulnerable to hypoxia.

These studies reinforce the importance of being assessed by a specialist in sleep medicine and receiving treatment for sleep apnea. Tanzi advised that you should work with your physician to 'keep your brain healthy' and free of amyloid, which can lead to Alzheimer's disease and cognitive decline.