Common Sleep Disorder Tied to Changes in Part of Brain Linked to Alzheimer's, Study Suggests

A common sleep disorder could cause changes in the brain also seen in those with early stage Alzheimer's disease, a study has suggested.

Obstructive sleep apnea (OSA) is a relatively common sleep disorder where a person's breathing is interrupted when the walls of their throat relax and narrow.

Symptoms of the condition include loud snoring and breathing noisily, gasping and snorting during sleep. Some also experience night sweats, and need to urinate frequently during the night. It is feared the resulting interruptions of oxygen supply to the body shrink the brain's temporal lobes, which help to store memories and appear to be affected in those with Alzheimer's and other forms of dementia. Most common in older people, OSA is already linked to conditions such as cancer, stroke and cardiovascular disease.

Professor Sharon Naismith, author of the study from Australia's University of Sydney School of Psychology, told Newsweek: "We found that reduced blood oxygen levels during sleep are related to reduced thickness of the brain's cortex in both the left and right temporal areas, regions that are important in memory and are early sites of injury in Alzheimer's disease."

"Indeed, reduced thickness in these regions was associated with poorer ability to learn new information, thereby being the first to link this structural change to memory decline."

Given that there are no cures for dementia, finding the key factors that contribute to or speed up cognitive decline are of "paramount importance," said Naismith.

Between 30 to 50 percent of the risk factors of dementia—such as depression, high blood pressure, obesity and smoking—are preventable, said Naismith. So the researchers wanted to understand where sleep disorders stand in this regard.

To test their hypothesis, they enlisted 83 people between 51 and 88 years old who had complained to their doctor of problems with their memory and moods, but had not been diagnosed with OSA.

The researchers tested the participants' memory skills and for symptoms of depression.

The individuals also visited a sleep clinic. There, equipment measured signs of OSA, including their brain activity, oxygen levels in the blood, heart rate, breathing and movements during sleep. They also underwent brain MRI scans to document their brain thickness.

Participants with low levels of oxygen in their blood while they slept were found to have thinner left and right temporal lobes of the brain. For the first time, scientists were able to link these changes with a dampened ability to learn new information.

In individuals showing signs of OSA, other parts of the brain appeared thicker, indicating the organ was reacting to the stress of having oxygen cut off by increasing swelling and inflammation.

Because of this apparent relationship between OSA and poor brain function, screening older people for OSA and treating the condition as soon as possible could therefore be a useful approach for preventing dementia, the study authors said. Younger people with OSA should also be vigilant, said Naismith.

"Given the clinical importance of this sample of at-risk older adults, we need to be screening older adults for sleep-disordered breathing," said Naismith. "In addition, for older adults presenting to sleep clinics, we should be asking patients about changes in their memory and other thinking skills and obtaining formal testing in some cases."

OSA can be treated using a continuous positive airway pressure (CPAP) device, which keeps airways open during sleep.

"Given there are no cures for dementia, early intervention is the key. Given we have gold-standard treatments for sleep-disordered breathing, we have a real opportunity to prevent cognitive decline caused by OSA before it's too late," said Naismith.

Next, the researchers will investigate whether CPAP equipment can be used to prevent cognitive decline in those with mild impairments.