October 16, 2015
Fitful sleep may cause changes in the brain that increase the risk of Alzheimer’s disease, a new study found. Scientists at the University of California, Berkeley, found that a lack of deep, restorative slumber can increase the buildup of beta-amyloid, a toxic protein that builds up in the brains of those with Alzheimer’s disease.
“Our findings reveal a new pathway through which Alzheimer’s disease may cause memory decline later in life,” said Matthew Walker, a professor of neuroscience at Berkeley and the senior author of the study, which was published in the journal Nature Neuroscience.
He notes that the findings may have an upside: Promoting sound sleep may boost the brain’s memory capacity. Exercise, cognitive-behavioral therapy and other measures have been shown to promote sound sleep and could have potential for helping to allay the ravages of Alzheimer’s disease.
“This discovery offers hope,” Dr. Walker said. “Sleep could be a novel therapeutic target for fighting back against memory impairment in older adults, and even those with dementia.”
Earlier studies in animals have shown that poor sleep may lead to beta-amyloid buildup in the brain. A 2013 study at the University of Rochester, for example, showed that in mice, a lack of rapid eye movement (REM) sleep, the phase of sleep when dreaming occurs, led to high levels of beta-amyloid in the brain. REM sleep, the researchers concluded, appeared to “clean” the brain, washing away toxic metabolites like beta-amyloid.
The current study was conducted in 26 older adults, aged 65 to 81, none of whom had Alzheimer’s or other forms of dementia. They were given brain scans to assess evidence of beta-amyloid buildup, and tasked with memorizing 120 pairs of words.
After a night’s sleep, during which their brain waves were measured to assess how soundly they slept, they were tested again.
The researchers found that, in general, those who had the highest levels of beta-amyloid in the medial frontal cortex, a part of the brain critical for longer-term memory, performed worst on memory tests the following morning. Some of the study participants forgot more than half of what they had memorized the previous day.
“The more beta-amyloid you have in certain parts of your brain, the less deep sleep you get and, consequently, the worse your memory,” Dr. Walker said. “Additionally, the less deep sleep you have, the less effective you are at clearing out this bad protein. It’s a vicious cycle.”
It’s long been known that people with Alzheimer’s disease tend to sleep poorly and spend more time awake at night. But scientists have been uncertain whether poor sleep contributes to Alzheimer’s onset, or if troubled sleep is actually an early symptom of Alzheimer’s.
Earlier studies have also shown that poor sleep can lead to memory and thinking problems, even in healthy people. People with a common breathing disorder called sleep apnea, which causes sleepers to awaken briefly hundreds of times during the night, has also been linked to memory problems and an increased risk of dementia.
But the researchers of the current study suspect that poor sleep may have a causative role in Alzheimer’s onset. “The data we’ve collected are very suggestive that there’s a causal link,” said Bryce Mander, the lead author of the study. “If we intervene to improve sleep, perhaps we can break that causal chain.”
This small study is interesting because it shows that poor sleep affects memory and may modify the effects of beta-amyloid buildup in the brain. However, it does not rule out the possibility that poor sleep is a symptom of brain changes related to Alzheimer’s disease, rather than a cause of such brain changes. If poor sleep causes the brain changes, then, as the study authors note, getting better sleep could lower the risk of Alzheimer’s. Nevertheless, poor, fitful sleep is likely to harm the body in many ways, such as increasing the risk for heart disease, which is itself a risk factor for developing Alzheimer’s. Improving your general health and reducing your risk of heart and other diseases could lower your risk of developing dementia later on.
Source: Bryce A. Mander, Shawn M. Marks, Jacob W. Vogel, et al: “Beta- amyloid disrupts human NREM slow waves and related hippocampus-dependent memory consolidation.” Nature Neuroscience, published online June 1, 2015.