Sleep apnoea, the condition that robs sufferers of deep sleep by endlessly and subconsciously waking them up, becomes more common as people age. Now, a small new study raises the possibility that it may somehow cause - or be caused by - Alzheimer's disease.
Don't worry just yet if you have sleep apnoea. The research is preliminary, and it's possible that there may be no connection between the two conditions. Still, scientists found that slimmer seniors with signs of disrupted breathing during sleep were more likely to have indicators of developing Alzheimer's disease.
"This is just a correlation," said study lead author Dr Ricardo Osorio, a research assistant professor at the New York University School of Medicine, in New York City. But, he said, the prospect of a connection deserves further study since there may indeed be a link between sleep, ageing and memory, which severely declines in Alzheimer's patients.
Sleep changes as you get older
"It's clear that sleep is important for memory, and sleep changes as you get older," he said. "Disrupted breathing during sleep also increases with aging."
People who have sleep apnoea often don't know it. They have trouble staying in deep sleep because their throats close as they slumber, temporarily blocking their airways and requiring them to subconsciously wake up to get air. Some sleep apnoea sufferers may awaken 35 or more times an hour.
In the new study, researchers tested the sleep of 68 seniors in their 60s, 70s and 80s. Their average age was 71.
A quarter of them had symptoms of moderate to severe breathing problems during sleep (a sign that they may have sleep apnoea), and about 49% had mild breathing problems. But none of them complained of sleepiness or concentration problems, which sleep apnoea can cause, Osorio said.
The researchers discovered that thinner participants with breathing problems during sleep were more likely to have "biomarkers" - biological signs - of an increased likelihood of developing Alzheimer's. These signs indicate brain damage and decreased use of glucose (the sugar that blood transports) in the brain, Osorio said.
"We do not know if these people will develop Alzheimer's in the future, and we don't know how much risk they have," he said. "In the future, we might able to predict the risk."
Risk of sleep apnoea
Although excess weight raises the risk of sleep apnoea, the obese participants with breathing problems didn't appear to have as much of an extra risk of Alzheimer's. There's another twist, Osorio said: For reasons that are unclear, being slightly overweight seemed to actually lower the risk of Alzheimer's.
So what's going on? The study doesn't give hints about which came first - Alzheimer's or sleep breathing problems - or whether something else, such as ageing, might be causing both.
Another expert said it's clear that thinking skills may be impaired in patients with sleep disorders such as sleep apnoea. "[But] the mechanisms of this are not well understood," said Dr Brad Dickerson, an associate professor of neurology at Harvard Medical School in Boston.
As for the study, Dickerson said its findings are intriguing. However, he said, "these findings are very preliminary, and need to be further studied ... in order to make sure they are consistent and to better understand their implications."
The next step, Osorio said, is to launch a study of older people with sleep breathing problems and monitor them over time to see if they're less likely to develop Alzheimer's after getting treatment to improve their breathing.
The study is scheduled to be presented Sunday at an American Thoracic Society conference in Philadelphia. Findings presented at medical meetings typically are considered preliminary until published in a peer-reviewed journal.
For more about Alzheimer's disease, try the US National Library of Medicine.