Why Getting Enough Sleep Is Crucial For Brain Health

10 ways to optimize sleep via the glymphatic system

Hello, everyone. I had a beautiful drive home from Colorado to Wyoming yesterday. It started with a full moon falling on snowy peaks that went from pink to peach to orange. Barbara Kingsolver’s Demon Copperhead kept my attention for eight solid hours, even though I couldn’t get past the first chapter of the hardcopy. As my dog Orzo snoozed next to me, I was somewhat envious as he cycled through many phases of sleep—from complete stillness to raspy deep breathing to vivid running and barking dreams. Sometimes I wish I could sleep as soundly as my dogs! 

How did you sleep last night? If you are like 40% of Americans, the answer is probably “not great.” The quest for a good night’s sleep gets progressively more challenging with age. And yet there are many simple things one can do to achieve the recommended 7 to 8 hours of sleep each night. Just like exercising and following a brain-healthy way of eating, sleep optimization is an important facet of taking care of your brain. In fact, poor sleep throughout life may predispose someone to developing Alzheimer’s later. 

I am putting my top sleep tips here first. Make sure you have folded these science-based habits into your nightly routine! To go deeper into the science of sleeping better, you’ll want to think about activating your brain’s glymphatic system. More on that below.

Sleep has its own vocabulary.
Find definitions of sleep terms in a full glossary at the end of this post.

My Top Sleep Tips For a Healthy Brain

1. Have a consistent bedtime and wake-up time each day. Sleep schedules aren’t just for children—adults thrive on consistency, too. Sticking to your schedule, even on weekends, is probably THE most important habit for optimizing sleep. Staying up late on weekends creates a social jetlag situation that contributes to the brain’s overall sleep debt.

2. Schedule a winding down time, too. When my watch alarm goes off at 9 pm, it reminds me that it’s time to get mentally prepared for sleep. Electronics get switched off, lights dim, and I begin my pre-sleep routine. A relaxing activity like reading, listening to music, or taking a bath, helps the brain switch gears for better sleep efficiency.

3. Control your sleep environment. Your bedroom should be dark, quiet, cool, and free of electronics. Earplugs, eye shades, and a weighted blanket can help get you into the sleep zone. 

4. Take a hot bath or shower before bed. After you’ve immersed yourself in warmth, it triggers a sleep-inducing drop in core body temperature. To make the most of this physiological perk, go straight from the bath to bed. 

5. Nap strategically. A well-timed nap can help pay off your sleep debt, but nap too late in the day and it can impact your ability to fall asleep later. If you nap, shoot for under one hour and before 3 pm.

6. Avoid alcoholic beverages before bed. While alcohol has a sedating effect that can help one fall asleep, it also has an activating component that kicks in as it metabolizes, usually between 2 and 4 am. Everyone metabolizes alcohol at a different rate. Not drinking at all is definitely the best way to optimize sleep. If you drink, be aware that it can clobber your sleep architecture; most people should avoid alcohol at least 3 hours before going to bed.

7. Avoid heavy meals before bed. Your brain’s glymphatic system will work more efficiently if you go to bed with an empty stomach.

8. Limit fluids at night. Getting up to go to the bathroom is a common sleep interruptor, especially if you find it difficult to fall back asleep. Focus on staying hydrated throughout the day, but back off on fluids after 6 pm. 

9. Know your caffeine curfew. Just like with alcohol, everyone has a slightly different tolerance for caffeinated beverages and food. Caffeine sticks around in the bloodstream for a long time. When you drink a cup of coffee, it takes 12 hours to reduce the caffeine in your system by just half. Much of the caffeine ingested in the afternoon is still in your bloodstream when you go to bed, making it difficult to fall asleep or get into productive sleep cycles. 

10. Keep a gratitude journal. The simple act of writing down 3 things each night that you are grateful for has been shown to improve both sleep quality and quantity. A beautiful gratitude journal (like this one at Wordaful) can help keep you motivated.

While You Sleep, The Brain Cleans Up

You know that feeling you get after a good night’s sleep? You face the day with a clear head, enthusiasm, and boundless energy. That’s the work of the brain’s glymphatic system (GS). “Glymphatic” is a mash-up of the words “glial” and “lymphatics.” Glial cells (Latin for glue) protect and insulate nerve cells in the brain. Lymphatics are a waste disposal system found elsewhere in the body. 

Think of the glymphatic system as the brain’s own garbage disposal. While you sleep, the GS gets to work filtering out substances that lead to chronic inflammation in the brain. It does this by gently squeezing the fluid-filled spaces in the brain (called vacuoles) which sets up a pressure gradient. Inflammatory particles and unwanted proteins get filtered into the cerebrospinal fluid and are eventually excreted. 

Source: The Glymphatic System: A Beginner’s Guide. Jessen et al, Neurochem Res, May 2015. Used with permission.

The GS works in concert with the brain's blood brain barrier (BBB) to create a directional flow of fluid to get rid of waste. Much research in Alzheimer’s now focuses on the integrity of the BBB.  We used to think that this wall-like layer of tightly-knit cells kept the brain protected from unwanted substances at all times. Now we know that the BBB gets sloppy with age. A leaky BBB leads to a constant influx in inflammatory particles, sticky proteins, and other toxin-like things. In a person with Alzheimer’s, the glymphatic system is impaired and the BBB is especially disordered.

Alzheimer’s and Sleep

It’s well-documented that getting too little sleep over decades significantly raises the risk of being diagnosed with Alzheimer’s. When researchers discovered that amyloid and tau were getting shuttled out of the brain by this drainage mechanism, it provided a reason why. Sleep quality deteriorates with age in just about everyone. But a rapid decline in a particular phase of sleep—deep NREM sleep—often precedes a diagnosis of Alzheimer’s by several years. 

It is still not clear what comes first—the sleep impairment or Alzheimer's. In reality, there seems to be a vicious cycle in which the brain fails to kick into clean up mode leading to a buildup of amyloid and tau. As these proteins accumulate, deep sleep deteriorates more which further impairs the glymphatic system. This study using PET scans to measure amyloid protein shows that levels go up after even just one night of poor sleep.

While researchers are still working out the mechanism of how sleep impacts dementia risk, what we do know is this: certain habits can activate the glymphatic system. Other habits can really keep the GS from doing its job. So while we all want to achieve high-quality sleep because it helps us feel and function at our best, we also need to be keeping our glymphatic systems in tip-top shape. 

Here’s How To Promote an Active Glymphatic System 

Ninety percent of glymphatic action happens during sleep. Many of the science-proven sleep habits I noted above work because they have a positive impact on sleep cycles, and in turn, the activity of the GS. In addition, these factors have been linked to glymphatic activity:

• Eat within a dedicated window. Intermittent fasting (IF) limits the hours in a day when you enjoy your food. Eating is typically restricted to the hours between late morning and early evening. While practicing IF has not yet been proven to reduce Alzheimer’s risk, avoiding nighttime eating does activate the GS. If you stop eating several hours before bed (see #7, above), your brain is more likely to shift into clean-up mode. 

• Stay physically active. The health of the BBB and its neighboring glymphatic system is dependent on a healthy cardiovascular system. Regular exercise keeps the smallest blood vessels that supply the brain healthy and functional throughout life.

• Limit alcohol. Any level of drinking impairs the phase of sleep the GS depends on most—deep NREM. Plus, moderate to heavy drinking may have a direct effect on making the BBB more leaky.

• Get enough omega-3 fats. DHA and EPA, the omega-3s you get from fish, have specific jobs in the brain to keep the BBB in good shape. These fats boost the integrity of brain cell membranes, patch up damage caused by oxidative stress, and may stimulate GS action. Get DHA and EPA from shellfish, fish roe, algae, and fatty cold water fish like salmon, cod, herring, anchovies, sardines, tuna, and mackerel. (I went into omega-3s in this article about dietary fats and this one about supplements.)

It’s remarkable that the brain’s complex waste filtering system was only just discovered in 2012. Back when I was in medical school, sleep wasn’t thought to be a metabolically active state. Those brain vacuoles were just structures to be memorized, but no one knew why they existed. Now we know that sleep is crucial for vibrant brain health and the glymphatic system is one of the reasons why. 

There is much more to learn about sleep. For example, what do you do if you have a sleep problem? Are sleep medications a good idea? What’s the deal with sleep supplements like magnesium and melatonin? When does one need a sleep study? Does correcting sleep disorders lead to a reduced risk of Alzheimer’s? And should you be tracking your sleep with an app on your phone or a biosensor device (like a Whoop or an Oura ring)? Let me know what questions you have and I’ll cover them in an upcoming newsletter. 

The Brain-Gut Connection on PBS

We talk a lot about the gut microbiome here on BHK because it’s an important aspect of brain health. Dr. Emeran Mayer is one of my mentors in the field, so I was hugely honored when he asked me to have a small part in his new PBS documentary The Brain-Gut Connection. I also reviewed an advance copy of the cookbook he wrote to go with the series, Interconnected Plates (available soon). It’s a treasure trove of easy Mediterranean-style recipes. Check out the series and let me know what you think. (True confession: I haven’t had the courage to watch myself on TV yet!)

Founding Members: See You on December 11

Our next kitchen chat and cooking class is coming up! I am really looking forward to having you over to make Fig & Almond Snack Bars for holiday gifting (or keeping!). Founding Members is a tier of the newsletter that includes 4 kitchen chat/cooking classes each year plus bonus recipes. Everyone is welcome. Sign up or upgrade your subscription by December 10, 2023 to receive the zoom link and recipe.

That’s all for today. I’ll be back this weekend with a variation on my Butternut Squash and Coconut Curry—an easy, warming stew made mostly of pantry staples. Thank you for being a part of the BHK community. I hope you are all enjoying the recipes, soaking up the science, and sleeping well. 

Love,

Annie

Sleep Vocab

Glymphatic system. A recently discovered waste clearance system that utilizes perivascular channels to eliminate proteins and metabolites from the brain.

Blood brain barrier. A tight network of blood vessels that line the central nervous system which regulate the movement of ions, molecules, and cells between the blood and the brain.

Rapid eye movement (REM) sleep. The most active phase of sleep in which the brain is dreaming and the eyes jerk in different directions. It occupies about 20% of sleep time.

Non-rapid eye movement (NREM) sleep. The phase of sleep not associated with vivid dreaming, divided into 3 stages: N1 (light sleep), N2 (intermediate sleep), and N3 (slow-wave or deep sleep). It occupies about 10% of sleep time.

Sleep architecture. The repetitive pattern of the combination of sleep stages and cycles.

Sleep cycle. A period of time, lasting about 90 minutes, that includes the various sleep stages and repeats throughout the night.

Sleep debt. The accumulated deficit of sleep that occurs when someone doesn’t meet their daily sleep requirements.

Sleep hygiene. Recommendations for things to avoid in the hopes of improving sleep quality.

Sleep latency. The length of time it takes to fall asleep. On average, a healthy person falls asleep 10 to 20 minutes after lights out.

Sleep inertia. Feeling groggy, achy, or listless upon awakening.

Sleep efficiency. The percentage of time spent asleep while in bed. A normal sleep efficiency is considered to be 85% or higher.

Sleep procrastination. The tendency to put off going to sleep at night by finding other things to do.

Social jetlag. Disordered sleep due to staying up late on weekends.