Sleep apnea, a fairly common, treatable disorder that causes people to stop breathing momentarily while they sleep, may lead to cognitive impairment and even dementia, according to a new study of elderly women.
Women in the study with sleep apnea or other sleep disorders that affected their breathing were much more likely than those with normal sleep habits to develop cognition problems within five years, said researchers at UCSF and California Pacific Medical Center, who published the results in the Journal of the American Medical Association.
Sleep disorders, and sleep apnea in particular, have long been associated with memory loss and dementia in particular, but the study is among the first to strongly suggest that the sleep problems may be a cause – not an effect – of the cognitive impairment.
“The extent of information has been limited before, because the studies were based on people with advanced dementia who, surprise, surprise, had sleep problems. It’s been hard to tell what’s the chicken and what’s the egg,” said Dr. Kristine Yaffe, a professor of psychiatry, neurology and epidemiology at UCSF, who led the study.
“This study isn’t proof-positive, but it’s much stronger than earlier studies,” she said. “What we’re seeing is a nearly twofold increase of having cognitive problems five years later.”
A Thorough Study
The study of 298 women, who had an average age of 82, looked at all kinds of sleep disorders and took into consideration how many hours of sleep subjects got, how often their sleep was interrupted and, among those with sleep apnea, how often they stopped breathing during the night. Although the study looked only at women, it’s likely the results apply to men too.
Researchers found that only the breathing problems were strongly associated with an increased risk of developing cognitive impairment. Among women who had sleep apnea at the start of the study, 45 percent developed either mild cognitive impairment – often an early stage of dementia – or dementia after five years.
About 31 percent of women without sleep apnea developed cognitive impairment. None of the women had dementia at the start of the study.
Because sleep apnea is treatable, the study findings could have major public health implications, said doctors familiar with the research. Earlier studies have shown that treating sleep apnea can improve cognitive function, but it’s not yet known whether treatment could prevent dementia, and clinical trials will need to be done.
About Brain Health
Aside from the treatment perspective, the study also suggests intriguing questions into what role sleep plays in long-term brain health. Increasingly, doctors are discovering that it’s not just the amount of sleep people get, but the quality and structure of that sleep that matters.
“It’s a million-dollar question: What does sleep do?” said Luis de Lecea, an associate professor of psychiatry and behavioral sciences at Stanford who has studied sleep disorders and memory loss in mice and other animals. “There’s quite a broad consensus that supports the notion that memories are consolidated during sleep. But obviously the field is still not clear about what the mechanisms for memory formation are.”
And the new research, he said, shows a “much more dramatic effect” from sleep disorders than simple memory loss. “Cognitive impairment is a whole different ballgame.”
Authors of the dementia study said their work wasn’t designed to describe exactly what happens in the brain that creates the association between sleep apnea and cognitive impairment. But because their study clearly showed a relationship between hypoxia – or low levels of oxygen for sustained periods of time during sleep – and dementia, that’s probably a good place to focus subsequent studies, they said.
Some animal studies have found a connection between hypoxia and buildup of beta amyloid, the material that collects like plaque in the brains of Alzheimer’s patients. Other studies have tied low oxygen levels to increased brain inflammation.
A New Perspective
Whatever may be happening, the results of the study could change how doctors and patients view sleep apnea and other sleeping disorders, said the study authors and other researchers.
Dr. Marci Teresi, clinical lead of the Kaiser Permanente Santa Clara Memory Clinic, said she often tests dementia patients for sleep apnea and other sleeping disorders. It’s intriguing to think that early treatment of sleep apnea could prevent, or maybe slow down, cognitive problems, she said.
But one downside is that treatment of sleep apnea isn’t easy – patients must sleep with a mask on their face that forces their airway to remain open and keeps them breathing. The masks can be uncomfortable and hard to get used to, and as many as half of patients give up on them after a while.
“I have plenty of patients who struggle with the mask,” Teresi said. “But if this is something we could actually treat and prevent dementia, that would be great.”
Source: By Erin Allday, San Francisco Chronicle, Aug. 10, 2011 (http://www.sfgate.com/cgi-bin/article.cgi?f=/c/a/2011/08/09/MNJK1KLC2V.DTL)