Sleeping little throughout life is associated with a higher risk of suffering Alzheimer. But, paradoxically, it is also sleep too much.
Although scientists are certain that there is a connection between the dream and the dementiaThe nature of that connection is complicated. It could be that too little sleep triggers changes in the brain that cause dementia. Or it could be that people’s sleep is disrupted by an underlying health problem that also affects brain health. And changes in sleep patterns can be an early sign of dementia itself.
Below are expert opinions on these various connections and how to assess risk based on your own sleep habits.
Sleep a little
Sleep acts as a nighttime shower for the brain, washing away cellular waste that has built up during the day. During this process, the fluid surrounding brain cells removes molecular debris and transfers it into the bloodstream, where it is filtered by the liver and kidneys and expelled from the body.
That junk includes the protein amyloid, which is thought to play a key role in Alzheimer’s disease. Everyone’s brain produces amyloid during the day, but problems can arise when the protein builds up into sticky clumps, called plaques. The longer you’re awake, the more amyloid builds up and the less time your brain has to clear it away.
Scientists don’t know whether getting too little sleep on a regular basis — typically considered six hours or less a night — is enough to trigger amyloid buildup on its own. But research has found that among adults ages 65 to 85 who already have plaques in their brains, the less sleep they had, the more amyloid they had and the worse their cognition.
“Is lack of sleep enough to cause dementia? Probably not on its own,” said Dr. Sudha Seshadri, founding director of the Glenn Biggs Institute for Alzheimer’s and Neurodegenerative Diseases at the University of Texas Health Science Center at San Antonio. “But it certainly seems to be a risk factor for increasing the risk of dementia, and perhaps also the rate of decline.”
People with Alzheimer’s may start to develop symptoms in their 60s or 70s, but amyloid can begin to build up as much as two decades earlier. That’s why it’s important to prioritize sleep, aiming for seven to nine hours a night, starting in your 40s or 50s, if not earlier, says Joe Winer, a postdoctoral fellow in neurology and neurological sciences at Stanford University’s Sleep and Circadian Sciences Center.
“We don’t have a great answer to, for example, whether sleep in your 20s influences risk later in life,” Dr. Winer said. “But I think the evidence is that probably in midlife, as you get into your 60s and 70s, your sleep is going to be important.”
Some sleep disorders, particularly sleep apnea, are also associated with an increased risk of dementia. This may be because sleep apnea disrupts people’s sleep, or because it tends to occur in people who are overweight or have diabetes, which are also linked to dementia.
But even when you strip out the effect of these other problems, sleep apnea appears to confer its own independent risk for dementia, says Dr. Diego Carvalho, an assistant professor of neurology at the Mayo Clinic Sleep Medicine Center. That may be because sleep apnea limits the amount of oxygen reaching the brain, which can increase brain inflammation and damage blood vessels and cells.
Too much sleep
At the other end of the spectrum, sleeping too much also appears to be linked to an increased risk of dementia, although perhaps more indirectly.
If a person regularly stays in bed for more than nine hours a night, or takes multiple naps during the day, it may be a sign that they are sleeping very poorly, which could increase their risk of Alzheimer’s disease for the reasons mentioned above.
Another possibility is that the need for excessive sleep is related to a mental or physical disability. Mental disorders, such as depression, and physical disorders, such as diabetes or cardiovascular problems, are associated with an increased risk of dementia, as are physical inactivity, loneliness and isolation.
“At this time, there is no clear causal role for prolonged sleep in relation to dementia,” said Dr. Carvalho. “It may be more of a symptom of an underlying problem than the cause of the problem.”
An early symptom?
Some of the first areas of the brain affected by Alzheimer’s are those that help regulate sleep and circadian rhythms. As a result, people who develop the disease may experience sleep problems even before they show signs of memory loss or other symptoms.
Along with amyloid, the other main protein thought to cause Alzheimer’s disease is called tau. Like amyloid, tau also builds up in the brain and eventually damages brain cells. One of the first places tau buildup appears “is in these areas of the brain stem that are important for regulating sleep and wakefulness,” explains Dr. Winer. “So we think that the appearance of tau in these areas is going to disrupt people’s sleep-wake cycles very soon.”
Sleep problems can also be an early sign of other common types of dementia. In Lewy body dementia and Parkinson’s disease dementia, for example, sleep is sometimes interrupted by rapid eye movements, causing people to act out their dreams — something their bed partner might notice, Dr. Seshadri said.
“Normally, when you have this rapid eye movement sleep, that’s the time when the muscle tone in your body drops to almost zero, so your muscles don’t move,” he explained. “In REM sleep, this suppression of muscle tone is lost, and that’s why your muscles actually move like in dreams.”
Experts say it’s normal for older people to sleep a little more or a little less after retirement, or to wake up and go to bed a little earlier or later than they used to. But if there’s been a drastic change, consider consulting your doctor or a sleep specialist.
“If someone is waking up at two or three in the morning, or sleeping three hours during the day, that’s a cause for concern,” says Dr. Seshadri. “If someone is waking up an hour earlier than they used to and taking a 30- to 60-minute nap during the day, that’s much more likely normal aging.
#poor #sleep #affects #dementia #risk
