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Sleep disorder linked to brain changes indicative of dementia

Drop in oxygen caused by obstructive sleep apnoea may be linked to shrinkage of temporal lobes

Caroline White

Friday, 06 July 2018

Obstructive sleep apnoea (OSA) may be linked to changes to the structure of the brain that are also seen in the early stages of dementia, suggests research* published in the European Respiratory Journal.

OSA is known to reduce levels of oxygen in the blood. It is this drop in oxygen which may be linked to a shrinking of the brain’s temporal lobes and a corresponding decline in memory, the researchers say.

Screening older people for OSA and treating the condition where needed could help prevent dementia in this group, they suggest.

Up to half of the risk for dementia is due to modifiable factors, such as depression, high blood pressure, obesity and smoking, but various sleep disorders have also emerged as potential risk factors.

The researchers therefore decided to look specifically at whether OSA might affect the brain and cognitive abilities.

They studied 83 people, aged between 51 and 88 years, who had visited their doctor with concerns over their memory or mood but had not been diagnosed with OSA. Each 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 which records brain activity, levels of oxygen in the blood, heart rate, breathing and movement.

People with low levels of oxygen in their blood while they were sleeping tended to have thinner left and right temporal lobes of the brain. These are regions known to be important in memory and are affected in dementia.

This alteration in brain structure was linked to a reduced ability to learn new information─ the first time a direct link of this kind has been shown.

On the other hand, people with signs of OSA were also more likely to have increased thickness in other regions of the brain, which the researchers say could be the brain reacting to lower levels of oxygen with swelling and inflammation.

OSA is more common in older people and has already been linked to heart disease, stroke, and cancer, but it can be treated with a continuous positive airway pressure (CPAP) device, which prevents airway closure during sleep.

Lead author Professor Sharon Naismith from the University of Sydney, Australia, commented: “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.”

*Cross E. N, Memarian N, Duffy L. S, et al. Structural brain correlates of obstructive sleep apnoea in older adults at risk for dementia. Eur Respir J 2018; 52: 1800740 DOI: 10.1183/13993003.00740-2018.

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