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Too Little, or Too Much, Sleep Tied to Higher Alzheimer’s Risk

September 21, 2021

Sleeping fewer than six hours a night, or more than nine hours a night, is tied to an increased risk of developing Alzheimer’s disease, researchers report. The findings, from one of the largest analyses to date, add to growing evidence that healthy sleep patterns are critical for brain health. Experts generally advise we get seven to eight hours a night, and this sleep “sweet spot,” this and other studies show, may help to keep our thinking and memory skills sharp. 

For the study, published in JAMA Neurology, researchers at Stanford University School of Medicine looked at 4,417 men and women who ranged in age from 65 to 85. They were part of a large and ongoing study of brain health involving dozens of medical centers in the United States, Canada, Australia and Japan.  

All the study participants had assessments of thinking and memory skills and were cognitively healthy, with no signs of Alzheimer’s disease or other serious memory problems. They had all undergone PET brain scans so assess levels in the brain of beta-amyloid, a toxic protein component that builds up in the brains of those with Alzheimer’s disease. They also filled out detailed questionnaires about their sleep habits, including how many hours of sleep they typically got at night and how often they napped during the day. 

The researchers found that those men and women who typically slept six or fewer hours a night scored lower on tests of memory function, compared to those who got the normal seven or eight hours a night. They also had higher levels of beta-amyloid buildup in their brains. High levels of beta-amyloid are associated with an increased risk of developing Alzheimer’s disease. 

Those who slept nine or more hours a night also tended to score lower on tests of memory and thinking skills, though they did not have higher levels of beta-amyloid in the brain than the healthy sleepers. Excess sleep had a particularly detrimental effect on executive function, which allow us to plan, organize and remember instructions. Those who slept a lot also scored higher on assessments of depression, which has been linked to an increased risk of developing Alzheimer’s disease. 

Both the short sleepers and the long sleepers also tended to have a higher body mass index. A high BMI indicates being overweight or obese, which is also a risk factor for Alzheimer’s disease and other forms of dementia. Both groups were also more likely to take longer naps during the day than normal sleepers, suggesting that excessive napping may also be an early sign of impaired thinking and memory problems down the road. 

Other studies have shown that poor sleep is associated with an increased risk of Alzheimer’s disease, depression, obesity, heart disease and other problems. This large analysis adds more evidence that too little, or too much, sleep may be bad for the brain. 

Deep sleep is thought to have a cleansing function, ridding the brain of toxic debris that can damage neurons. As many as one in three people suffer from insomnia and other sleep problems, and poor sleep and short nights of sleeping are especially common in older people. 

Whether improving sleep can actually fend of Alzheimer’s disease remains unproven, though this and other studies suggest that the right amount of sound sleep is good for the brain. While doctors often prescribe sleeping pills for those with insomnia, drugs can interfere with our sleep architecture, the normal pattern of deeper and lighter sleep stages we go through at night, and not be as restorative as we would like. Drugs also have side effects, and some have been tied to an increased risk of developing dementia. 

A better alternative for those with insomnia is cognitive behavioral therapy, or CBT, a psychological therapy that teaches people to address the underlying behaviors and beliefs that are disrupting their sleep. Good sleep hygiene is also important. Try to maintain a regular sleep schedule, going to bed and waking up around the same time each day. Limit the bedroom to sleeping, and not watching TV or staring at the computer screen, which can emit light that disrupts sleep by over-stimulating the brain. Avoid heavy meals in general just before bed, as well as physical activity, frustrating situations and animated discussions that may cause anxiety. If you can’t get to sleep after 25 minutes or so, get out of bed and try reading a book or another restful activity, then return to bed when you feel sleepy. 

A sleep doctor can also address issues that disrupt sleep, including sleep apnea, marked by snoring and waking up many times for brief periods throughout the night. Sleep apnea has been tied to an increased risk of Alzheimer’s disease. If you are sleeping too much, a doctor can screen for depression or other medical conditions that may be disrupting your sleep cycles. 

By ALZinfo.org, The Alzheimer’s Information Site. Reviewed by Marc Flajolet, Ph.D., Fisher Center for Alzheimer’s Research Foundation at The Rockefeller University. 

Source: Joseph R. Winer, PhD; Kacie D. Deters, PhD; Gabriel Kennedy, BSc; et al: Association of Short and Long Sleep Duration With Amyloid-β Burden and Cognition in Aging. JAMA Neurology, August 30, 2021

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