As people age, they often find a sound night’s sleep is harder to get. Sometimes this change is a natural result of aging, but now experts are learning that for the elderly, a lack of sleep might lead to Alzheimer’s disease.
Sleep apnea, a breathing disorder, can wake people from slumber tens of times an hour. Given what researchers know about the importance of sleep for brain health, there is concern that sleep apnea could worsen Alzheimer’s disease.
“The evidence for this connection is very strong,” says Said Mostafavi, M.D., the Chief Medical Officer for Advanced Sleep Medicine Services Inc., and a sleep specialist. “When you look at the numbers and the prevalence of dementia in sleep apnea patients, as compared to the general population, it is very striking.”
Scientific Study of the Link Between Alzheimer’s and Sleep Apnea is Still Ongoing, but Connections are Emerging
Alzheimer’s disease is the most common cause of dementia. The National Institute on Aging reports that more than 5 million Americans may have the disease.
The disease progressively degenerates the brain that over time impairs memory and thinking skills, eventually shutting the body down completely. While it usually shows up in people over 60, Alzheimer’s disease is not considered a normal part of aging. It’s currently the 6th leading cause of death in the U.S.
More than 18 million Americans have sleep apnea. Given the evidence that the two disorders interact, and these numbers point to a significant health problem.
“A high percentage of people that develop loss of memory and thinking abilities or dementia due to Alzheimer’s disease have altered sleep,” says David Holtzman, M.D., professor and chairman of the department of neurology at Washington University School of Medicine in St.Louis, MO. “There is also emerging evidence that when the brain changes of Alzheimer’s disease begin, but before memory and thinking problems, sleep starts to become abnormal.”
Researchers are still trying to figure out whether sleep apnea increases the risk of Alzheimer’s disease, and if so by how much. A recent study gives some indication. In the study, researchers at the University of San Francisco determined that the women with sleep apnea were nearly twice as likely to develop cognitive impairment as they aged ^1.
“Even before studies came out linking Alzheimer’s and sleep apnea, I’d been talking to neurologists about it for years. We knew there was a relationship,” says Mostafavi. “We would see a bulk of Alzheimer’s patients who also had sleep apnea.”
Sleep Apnea’s Harmful Effects Damage the Brain
Researchers are working hard to understand exactly how neurons, blood vessels and chemical signals used by the body interact and influence each other in sleep apnea and Alzheimer’s disease.
Sleep disturbances are common in people with Alzheimer’s. Up to 45 percent of patients experience symptoms such as nighttime awakenings, need for naps and sleep fragmentation ^2.
Changes in sleep are normal during aging, but dementia can exacerbate such experiences. This can make the behavioral problems of Alzheimer’s and dementia worse. Sleep problems in Alzheimer patients are also a major risk for early institutionalization. Even if sleep disorders are present early in the illness, the problem can get worse over time with Alzheimers patients.
“Sleep is a restorative phase of our being,” Mostafavi says. “We think that during restful sleep, all the waste in the brain gets cleaned up. In an interrupted sleep, that scavenging is not done.”
For every apnea event, two major things happen to the body. Sleep is interrupted and the oxygen concentration in the blood drops. Both effects can adversely affect the brain.
“Animal studies have shown that amyloid-beta, the protein that accumulates in the amyloid plaques of Alzheimer’s disease, is higher in the brain during wakefulness and lower during sleep,” says Holtzman. “This appears to be due to lower production of amyloid beta by brain cells during sleep, as well as increased clearance of amyloid beta from the brain.” This clearance is the same waste-removal process Mostafavi mentioned.
“Low oxygen is directly related to causing brain damage,” Mostafavi says. “And one of the most vulnerable parts of the brain to a reduction in oxygen is the hippocampus.” This is a small horseshoe-shaped structure in each hemisphere of the brain, located near the center of the brain. It’s the place where long term memories are stored and is one of the first structures affected by Alzheimer’s disease.
Sleep Apnea May Make Dementia Worse
These biological connections may mean that the two disorders play off each other, sleep apnea making Alzheimer’s worse and vice versa.
In 2015, a study from researchers at New York University found that people with sleep apnea, on average, were diagnosed with mild cognitive impairment 10 years before their peers who didn’t have the breathing disorder ^3.
The sleep apnea patients in the study also seemed to experience an accelerated timeline for Alzheimer’s disease. People with the disorder who developed Alzheimer’s disease were diagnosed five years sooner on average than the non-sleep apnea sufferers.
Degeneration of the neural pathways that regulate sleep and the cycle of sleep and wake could be responsible for sleep apnea in Alzheimer’s patients. Sleep apnea could contribute to neural dysregulation through low oxygen levels or through alterations to blood vessels triggered by the body’s response to sleep apnea’s disrupted sleep and plunging oxygen levels.
However, the exact nature of the relationship between Alzheimer’s disease and sleep apnea still needs further exploration. “It will be important to prove for sure whether or not optimal sleep decreases risk for Alzheimer’s disease and whether poor sleep increases risk,” Holtzman says. “It will also be important to know whether specific treatments targeting sleep can decrease one’s risk for Alzheimer’s disease.”
Treating Sleep Apnea Helps Brain Health
There is no treatment for Alzheimer’s disease, which means it is important to treat conditions that could make the disease or its symptoms worse. Fortunately, treatment for sleep apnea is already an option.
“In addition to the other health benefits of getting a good night’s sleep, usually about 7 to 8 hours, depending on the person, getting that full night’s rest may decrease one’s risk of getting dementia due to Alzheimer’s disease,” says Holtzman.
Decreasing risk isn’t the same as improving Alzheimer’s after it occurs. “I can never say that dementia will definitely get better with treatment of sleep apnea,” Mostafavi says. “There is not a one-to-one relationship. This is the same with elevated blood pressure or other health risks associated with sleep apnea. But there is a possibility that treating the apnea can help other measures. There could be some improvement in memory, we don’t yet know.”
However, there are clear brain health benefits to getting enough sleep. The best treatment for sleep apnea—continuous positive airway pressure or CPAP therapy—also works for people with Alzheimer’s disease. A 2009 study pitted the effects of three weeks of CPAP therapy against three weeks of sham CPAP in 52 people with Alzheimer’s disease. Sleep recordings of the participants showed that even one night of therapy resulted in a better night’s sleep and three weeks translated to significantly deeper, sounder sleep ^4.
The NYU study examined the medical histories of 2,470 people to find that sleep apnea was associated with a faster decline in mental function. However, the study also showed that treating the sleep disorder could help. Those that sought treatment experienced a delay of 10 years in their diagnoses compared to those who didn’t.
Another small study of 23 patients with Alzheimer’s disease showed that progression of dementia slowed significantly over three years when they were treated for sleep apnea ^5.
These findings indicate that treating sleep apnea could keep the condition from hastening Alzheimer’s progression.
“The message has to be loud and clear to family practitioners, primary care physicians and ob-gyns that sleep apnea should be screened for,” Dr. Alon Avidan, a professor of neurology at the University of California, Los Angeles, and director for the UCLA Sleep Disorders Center told reporter Linda Carroll at NBC News.
Since the nighttime arousals of sleep apnea often don’t rise to a conscious level, sufferers may not be aware of their interrupted sleep.
“My advice for physicians is that if they have an elderly patient with any sign of dementia—not necessarily Alzheimer’s—they you should ask the relevant questions for sleep apnea,” Mostafavi says. “If they have the three hallmarks: daytime sleepiness, snoring, witnessed apneas. If any of these hallmarks show up, it is worth doing an overnight polysomnogram (PSG), the best test for sleep apnea.”
The harm from sleep apnea is done whether people realize it or not.
Are you concerned that you or a loved one may have sleep apnea? Take the interactive sleepiness quiz and share the results with your doctor:
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- Yaffe, K. et al., (2011). Sleep-disordered breathing, hypoxia, and risk of mild cognitive impairment and dementia in older women. JAMA, 306 (6), 613-619. PubMed
- Peter-Derex, L. et al., (2014). Sleep and Alzheimer’s disease. Sleep Med Rev., 19, 29-38. PubMed
- Osario , R.S. et al., (2015). Sleep-disordered breathing advances cognitive decline in the elderly. Neurology, 84 (19), 1964-1971. PubMed
- Cooke, J.R. et al. (2009). Sustained use of CPAP slows deterioration of cognition, sleep, and mood in patients with Alzheimer’s disease and obstructive sleep apnea: a preliminary study. J Clin Sleep Med., 5(4), 305-309. PubMed
- Troussière, A.C. et al. (2014). Treatment of sleep apnoea syndrome decreases cognitive decline in patients with Alzheimer’s disease. J Neurol Neurosurg Psychiatry. 85(12), 1405-1408. PubMed