Lack of sleep or waking up several times during the night may be bad for the brain and may increase the risk of Alzheimer’s disease, several new studies suggest. While a sound night’s sleep has long been advised for a sound body, the new research adds to a growing body of evidence linking sleep to brain health.

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. The new studies shed further light on the links between sleep and dementia.

In one study, researchers at the Johns Hopkins Bloomberg School of Public Health in Baltimore found that getting less sleep or sleeping poorly was tied to an increase in brain levels of beta-amyloid, a toxic protein that builds up and forms plaques in the brains of those with Alzheimer’s.

The researchers studied 70 older adults, average age 76, who were part of the ongoing Baltimore Longitudinal Study of Aging. Using brain scans, they found that those who said they got the least sleep, under five hours a night, or who slept fitfully had higher levels of beta-amyloid in the brain than those who slept over seven hours a night. The findings appeared in the journal JAMA Neurology.

The researchers couldn’t say whether poor sleep caused the accelerated buildup of beta-amyloid, or whether beta-amyloid accumulation was a cause of poor sleep. It’s also possible that both may be true: That poor sleep may cause beta-amyloid accumulation, and that enhanced beta-amyloid in turn disrupts sleep. They called for further research to study the relationship, as well as studies “to determine whether optimizing sleep can prevent or slow Alzheimer’s disease progression.”

“These findings are important, in part because sleep disturbances can be treated in older people,” said Dr. Adam Spira, the study’s lead author. “To the degree that poor sleep promotes the development of Alzheimer’s disease, treatments for poor sleep or efforts to maintain healthy sleep patterns may help prevent or slow the progression of Alzheimer’s disease.”

Additional research suggests that one reason why poor sleep may be linked to Alzheimer’s is that sleep may help to clear toxic molecules from the brain. Researchers at the University of Rochester Medical School found that when mice slept, the cells in their brains literally shrank, making more room for the flow of fluids through the brain. This increased flow of fluid acted something like the jet sprays in a dishwasher, flushing away harmful waste products like beta-amyloid.

“Sleep changes the cellular structure of the brain. It appears to be a completely different state,” said Dr. Maiken Nedergaard, a leader of the study, which was published in the journal Science. Similar results have been observed in other animal studies, and if these findings are shown to occur in people as well, they could explain how sleep may help to protect the brain.

In a third study, scientists at the University of Toronto found that sound sleep seemed to blunt the effects of APOE-E4, a gene that predisposes to the development of Alzheimer’s disease. For the study, also published in JAMA Neurology, researchers tested nearly 700 elderly men and women, monitoring their sleep and cognitive status at regular intervals. None had dementia at the start of the study.

Over the next six years, 98 of the participants developed Alzheimer’s, and 201 died. Their brains were examined for evidence of the plagues and tangles of Alzheimer’s disease.

The researchers found that in those who carried the APOE-E4 gene, those who slept most soundly showed the greatest preservation of memory and thinking skills. Among study participants who died, the poor sleepers were more likely to exhibit the characteristic brain plaques and tangles of Alzheimer’s disease.

Earlier studies have 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 poor sleep, as well as sleep apnea, is a common problem in the elderly. Just because you don’t sleep well doesn’t mean you will get Alzheimer’s disease. A sound night’s sleep, though, may be a critical component of a healthy lifestyle – and might even help to keep Alzheimer’s at bay.

By www.ALZinfo.org, The Alzheimer’s Information Site. Reviewed by William J. Netzer, Ph.D., Fisher Center for Alzheimer’s Research Foundation at The Rockefeller University

Sources: Adam P. Spira, PhD, Alyssa A. Gamaldo, PhD, Yang An, MS, et al: “Self-Reported Sleep and Beta-Amyloid Deposition in Community-Dwelling Older Adults.” Andrew S. P. Lim, MD; Lei Yu, PhD; Matthew Kowgier, PhD, et al: “Modification of the Relationship of the Apolipoprotein E E4 Allele to the Risk of Alzheimer Disease and Neurofibrillary Tangle Density by Sleep.” JAMA Neurology Oct. 21, 2013.

Xie et al “Sleep Initiated Fluid Flux Drives Metabolite Clearance from the Adult Brain.” Science, October 18, 2013. DOI: 10.1126/science.1241224