While You Get Your Zs, Your Brain's Cleaning House

08/18/2015 10:57 am ET Updated Dec 06, 2017

by guest blogger Pam Peeke, MD, MPH, FACP, best-selling author and expert on health, fitness, and nutrition

Are you one of the legions of z-less folks stumbling through the day, sleep deprived and constantly vowing that some day you'll make up for lost pillow time? I speculate that for most of you, the usual motivations for getting enough shut-eye are continuously going in one ear and out the other as life's seemingly ever-growing list of tasks gets in the way. But don't despair. I'm going to share with you a groundbreaking new reason to make sure a full night's sleep is on tonight's to-do list.

For years, the main purpose of sleep has eluded scientists. After all, when an animal is sleeping, it's vulnerable to predators. So sleep didn't seem to make evolutionary sense. And what's the reason for the wide spectrum of sleep needs within the animal kingdom? While giraffes sleep only an hour a day, brown bats can snooze for up to 20 hours per day. Researchers continued to grapple with this biological puzzle. Gradually, new studies emerged demonstrating the importance of sleep for mentation and energy. But something critical in our understanding of sleep was still missing.

Then, recently, a team at the University of Rochester made a revolutionary discovery: It turns out that it's while you sleep that your brain cleans house, removing metabolic waste. And by getting sleep you benefit from a decrease in your risk for dementia and other neurodegenerative diseases. What a mind-blowing and compelling new reason to prioritize getting your sleep!

This exciting new research uncovered the existence of a restorative function that occurs while we dream. We're actually clearing away the by-products or waste that accumulates as a result of all of our daily wakeful neural activities. Typically, the body uses the lymphatic system to dispose of its cellular waste. But this system does not extend to the brain. The brain maintains its own separate ecosystem, protected by the blood-brain barrier. Therefore, any brain cleansing is filtered through a unique glymphatic system that functions 24/7.

The system operates most efficiently while we're asleep because when we're awake, the energy needed to continually pump cerebral spinal fluid (CSF) is also being used to support attention and thinking. It's when we're sleeping that the majority of the energy is devoted to moving larger amounts of CSF to optimally rid the brain of waste. That's why researchers found that the glymphatic cleansing system is 10 times more active while we're snoozing away.

Here's how the brain-flushing process works:

1. The brain has two main functional operations: being awake and aware or being asleep and cleansed. Look at it this way. Consider an office building, bustling with meetings and work during the day. It's only when everyone goes home that the housekeeping team can get in there and clean up the waste.

2. The brain's waste products include toxic proteins like amyloid-beta and tau, which can lead to Alzheimer's disease, as well as to most other neurodegenerative diseases. If not cleared, these plaques and tangles can accumulate and disrupt healthy pathways, degrading the brain's cell connections and collapsing the neurons' transport system.

3. During sleep, your brain cells shrink in size by 60 percent, allowing waste to be most effectively removed from the brain. This shrinkage happens as a result of the drop in noradrenaline level that occurs with sleep. While awake, this activating hormone is essential in driving the fight or flight response. Researchers think that noradrenaline may be pivotal in controlling the expansion and contraction of brain cells during the sleep-wake cycle.

4. Brain imaging studies have shown that the cerebral spinal fluid bathing the brain is pushed through the glymphatic cleansing system, allowing waste products and toxins to piggyback on surrounding blood vessels and circulate throughout the rest of the body. Eventually they find their way to the liver, where the waste is processed and detoxed.

5. Brain cleaning is of paramount importance during sleep, but the brain is also performing other functions, such as consolidating memories and repairing and growing brain cells.

Here's something nifty to know: Body posture counts when it comes to the optimal way to dump brain waste. Using mice, scientists performed magnetic resonance imaging scans of the animals' brains while they were asleep and found that waste is best removed when the mice were sleeping in a lateral position. It turns out that our cerebral plumbing system works best when we're sleeping on our side. Happily, that's the most popular sleeping position for most humans, as is it for other warm-blooded mammals.

So, here's your takeaway: High-quality sleep is essential to maintaining a clean house in your brain. A good night's sleep helps to prevent the buildup of toxic proteins that will increase your risk of dementia. Sleep on your side when you can so you get optimal brain waste drainage. And the next time you feel inclined to cut your sleep short, remind yourself that even brains need to take out the trash!

Pamela Peeke, MD, MPH, FACP, is a Pew Scholar in nutrition and metabolism, an assistant professor of medicine at the University of Maryland, and a fellow of the American College of Physicians. As Senior Science Adviser to Elements Behavioral Health, she's creating an integrative lifestyle plan to support the treatment of addiction and mood disorders. A Senior Olympic triathlete, she is known as "the doc who walks the talk," living what she's learned as an expert in health, fitness, and nutrition. She is also the best-selling author of many books, including Fight Fat after Forty and Body-for-Life for Women. Her newest book is the New York Times bestseller The Hunger Fix.

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