Published today in The European Respiratory Journal, the study’s authors say the finding provides evidence that screening older people for obstructive sleep apnoea (OSA) and providing treatment where needed could help prevent dementia in this population.
OSA is a condition in which the walls of the throat relax and narrow during sleep, which stops breathing and is known to reduce blood oxygen levels. The new study indicates that the decline in blood oxygen levels may be linked to a shrinking of the brain’s temporal lobes and a corresponding decline in memory.
Diagnosing and treating obstructive sleep apnoea could be an opportunity to prevent cognitive decline before it’s too late.
Study leader, Professor Sharon Naismith of the University of Sydney's Brain and Mind Centre said: “Between 30 and 50 percent of dementia risk is due to modifiable factors, such as depression, high blood pressure, obesity and smoking. In recent years, researchers have recognised that various sleep disturbances are also risk factors for dementia. We wanted to look specifically at obstructive sleep apnoea and its effects on the brain and cognitive abilities.”
The researchers worked with a group of 83 people, aged between 51 and 88 years, who had visited their doctor with concerns over their memory or mood but had no OSA diagnosis. Each participant was assessed for their memory skills and symptoms of depression, and each was given an MRI scan to measure the dimensions of different areas of the brain.
Participants also attended a sleep clinic where they were monitored overnight for signs of OSA using polysomnography. This technique records brain activity, levels of oxygen in the blood, heart rate, breathing and movements.
The researchers found that patients who had low levels of oxygen in their blood while they were sleeping tended to have reduced thickness in the left and right temporal lobes of the brain. These are regions known to be important in memory typically affected in dementia.
These brain changes were also linked with participants’ poorer ability to learn new information. The researchers say this is the first time a direct link of this kind has been shown.
There is no cure for dementia so early intervention is key. On the other hand, we do have an effective treatment for obstructive sleep apnoea.
Conversely, patients with signs of OSA were also more likely to have increased thickness in other regions of the brain, which the researchers say could be signs of the brain reacting to lower levels of oxygen with swelling and inflammation.
OSA is more common in older people and has already been linked with heart disease, stroke and cancer, but it can be treated with a continuous positive airway pressure (CPAP) device, which prevents the airway closing during sleep.
Professor Naismith added: “We chose to study this group because they are older and considered at risk of dementia. Our results suggest that we should be screening for OSA in older people. We should also be asking older patients attending sleep clinics about their memory and thinking skills—and carrying out tests where necessary.
“There is no cure for dementia so early intervention is key. On the other hand, we do have an effective treatment for OSA. This research shows that diagnosing and treating OSA could be an opportunity to prevent cognitive decline before it’s too late.”
Professor Naismith and her team are now doing research to discover whether CPAP treatment can prevent further cognitive decline and improve brain connectivity in patients with mild cognitive impairment.
Professor Sharon Naismith is the Leonard P Ullman Chair in Psychology at the Charles Perkins Centre. She is also an NHMRC Career Development Fellow and Clinical Neuropsychologist who heads the Healthy Brain Ageing Program at the Brain and Mind Centre. Professor Naismith is co-chief investigator of the newly established Australian Dementia Network (ADNet).