Is there a better head position for sleeping (and clearing out junk)?

Some evidence would suggest yes.

Sleeping on our sides may be the best position for several reasons, if we can do it comfortably.

Before I present this post I want to add a few disclaimers.

First, there are a lot of unique considerations for individuals, including which sleeping positions are uncomfortable, impair breathing, complicate sleep apnea treatment, etc. A good article I read while preparing this post states: “Sleep habits are highly personal, and the same goes for your ideal sleep position. A side sleeping position has many advantages and fewer drawbacks than a stomach or back position. Ultimately, the position that helps you fall asleep, stay asleep, and get quality rest is the best one for you.”

Second, the science of how our brains wash out the accumulated junk of a full day’s cognitive work while we are sleeping is still very much being studied. There is fascinating stuff to learn, including the magic of the brain’s glymphatic system and washing cycle mode. As a primary care doctor I am not contributing to this research by any means. But I do have a vested interest in helping to prevent or slow neurodegenerative diseases like the ones I see every day (dementia, Parkinson’s, general cognitive decline, etc.)

The typical articles we read about preferred sleep positions concentrate mostly on our physical comfort, breathing, and associated medical issues. So I’m going to quickly summarize that and let the interested reader click through to more information if desired. But then I’m going to spend the bulk of this post examining an overlooked consideration - which sleeping position best clears out the brain of leftover metabolites and junk that can accumulate and lead to long term problems?

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Conventionally Discussed Pros and Cons

In short, side sleeping is generally considered the most beneficial position, offering advantages for spine alignment, reducing snoring and sleep apnea symptoms, and aiding digestion for most people. Everyone is different, and so following your body signals here goes a long way. For example, side sleeping may cause shoulder and hip pain, especially in older people. Forcing it will result in bad sleep. But one of the best tricks I learned along the way in this regard is to put a pillow between my knees while side sleeping. For me, this keeps my spine, hips, and knees in alignment and therefore happier in the morning. Some nuances between side, back, and front sleeping are discussed further in this article from The National Council on Aging (NCOA) as promised. And a bonus article from Houston Methodist on sleep positions.

What do we do at night?

The NCOA also did a survey of 600 people and found that almost 50% of respondents prefer to sleep on their side, 14% preferred their stomach, and 17% preferred their back. The other 19% had a mixed preference.

I ran a poll on another website I contribute to, and about 2,000 people responded, with a side sleeping self-reporting rate of 88%!

But in terms of observed reality, one study of sleeping habits found we actually do this: “participants spent 54.1% in the side position, 37.5% in the back position, and 7.3% in the front position.” Is there some advantage that our subconscious minds and bodies seek out for the majority of the night on our sides?

I almost always go to bed on my left side, and wake up in the morning on my right. Maybe there is something to that progression. Read on!

A New and Emerging Consideration

While much attention has been given to the duration and quality of sleep, emerging research suggests that our sleeping position may play a significant role in brain health. Recent studies indicate that sleeping on one's side could be the most effective position for cerebrospinal fluid drainage and brain waste clearance, potentially reducing the risk of neurodegenerative diseases such as Alzheimer's and Parkinson's. Sound a little unfounded? Maybe not.

What is the Glymphatic System?

To understand the potential importance of sleep position, we must first delve into the brain's waste clearance system - the glymphatic system. This complex network of vessels acts as the brain's cleaning crew, removing metabolic waste products that accumulate during wakefulness. It is primarily active during sleep, making our nightly rest crucial for maintaining brain health. The name is derived from “glial-dependent lymphatic transport” because of the role the brain’s glial cells play. I never learned of this system in med school, since apparently it was only discovered in 2012.

Cerebrospinal fluid (CSF) plays a vital role in this process. During sleep, CSF flows through the brain, exchanging with interstitial fluid (ISF) to flush out waste products, including proteins associated with neurodegenerative diseases such as amyloid beta and tau. This cleansing process is essential for maintaining cognitive function and potentially reducing the risk of developing neurological disorders. And if you’re into medical speak: “This glial cell-dependent paravascular network removes soluble proteins and metabolites from the central nervous system, but in addition supplies the brain with glucose, lipids and neuromodulators, utilizing paravascular tunnels formed by astroglial cells.”

In short, “the glymphatic system is the analog of the lymphatic system in the central nervous system. As such, the glymphatic system plays a key role in regulating directional interstitial fluid movement, waste clearance, and, potentially, brain immunity.”

The Role of Sleep Position in Brain Waste Clearance

Recent research elucidates how our sleep position may influence the efficiency of this cleaning process. A study conducted at Stony Brook University, and published in the Journal of Neuroscience, used dynamic contrast MRI to examine the glymphatic pathway in rodents. The researchers discovered that the side sleeping position was the most efficient for removing waste from the brain compared to prone (on the stomach) or supine (on the back) positions. This finding suggests that body posture during sleep could significantly impact the brain's ability to clear waste products and potentially influence long-term brain health.

To quote and paraphrase some study details:

The glymphatic pathway expedites clearance of waste, including soluble amyloid β (Aβ) from the brain. Transport through this pathway is controlled by the brain's arousal level because, during sleep or anesthesia, the brain's interstitial space volume expands (compared with wakefulness), resulting in faster waste removal. Humans, as well as animals, exhibit different body postures during sleep, which may also affect waste removal. Therefore, not only the level of consciousness, but also body posture, might affect CSF–interstitial fluid (ISF) exchange efficiency….

The analysis showed that glymphatic transport was most efficient in the lateral position compared with the supine or prone positions. In the prone position, in which the rat's head was in the most upright position (mimicking posture during the awake state), transport was characterized by “retention” of the tracer, slower clearance, and more CSF efflux along larger caliber cervical vessels. The optical imaging and radiotracer studies confirmed that glymphatic transport and Aβ clearance were superior in the lateral and supine positions. We propose that the most popular sleep posture (lateral) has evolved to optimize waste removal during sleep and that posture must be considered in diagnostic imaging procedures developed in the future to assess CSF-ISF transport in humans.

Why Side Sleeping May Be Superior

Several factors may contribute to the superiority of side sleeping for brain waste clearance that was seen in this study, and some other referenced at the end of this post:

• Gravity and fluid dynamics: The lateral position may allow for optimal gravitational flow of CSF and ISF, enhancing the exchange between these fluids and facilitating waste removal.

• Blood flow patterns: Side sleeping may influence cerebral blood flow in a way that promotes more efficient waste clearance.

• Anatomical considerations: The positioning of blood vessels and nerves in the lateral position may create better conditions for glymphatic system function.

• Evolutionary adaptation: The prevalence of side sleeping in humans and many other animals suggests that we may have evolved to favor this position for its benefits to brain health.

Implications for Neurodegenerative Diseases

The potential link between sleep position and brain waste clearance has significant implications for the prevention and management of neurodegenerative diseases. Conditions such as Alzheimer's and Parkinson's are associated with the accumulation of toxic proteins in the brain. If side sleeping indeed enhances the removal of these waste products, it could potentially reduce the risk of developing these disorders or slow their progression.

The Washing Machine of the Brain

A study published in the journal Science used functional magnetic resonance imaging (fMRI) to observe the movement of blood and CSF in the human brain during sleep. The researchers discovered rhythmic waves of blood and CSF that appeared to function like a washing machine's rinse cycle, potentially clearing the brain of toxic waste. Check out this video below. From the NIH Directors Blog:

First, you see a wave of blood flow (red, yellow) that’s closely tied to an underlying slow-wave of electrical activity (not visible). As the blood recedes, CSF (blue) increases and then drops back again. Then, the cycle—lasting about 20 seconds—starts over again.

The findings, published recently in the journal Science, are the first to suggest that the brain’s well-known ebb and flow of blood and electrical activity during sleep may also trigger cleansing waves of blood and CSF.

While this study didn't specifically focus on sleep position, it provides further evidence of the importance of sleep in brain waste clearance. The researchers observed that these cleansing waves were closely tied to slow-wave electrical activity in the brain, which is most prominent during deep sleep.

Practical Implications and Recommendations

I found another paper that was highly speculative, but well-referenced, so please take these recommendations with a grain of salt. They are logical, mostly harmless, but may or may not help. These may be proven someday to be effective hacks against neurodegeneration caused by a disruption of the glymphatic system. This is not the sole way that brain problems develop, of course, but nonetheless the authors are long on:

• Consuming omega-3 fatty acids (n3-PUFAs), particularly from marine-based fish oils, which can improve amyloid-beta clearance and reduce aggregate formation.

• Practicing intermittent fasting, especially alternate-day fasting, which can increase AQP4 polarization and boost glymphatic clearance. This seems like a massive lifestyle change for an unproven benefit to me.

• Adopting a right lateral sleeping position, which appears to be most efficient for glymphatic transport and CSF clearance.

• Moderate alcohol consumption in low doses (0.5 g/kg), which may increase glymphatic clearance, although excessive consumption should be avoided. I wrote a long post about the poison and pleasure of alcohol previously; it’s complicated, and drinking has risks.

• Engaging in regular physical exercise, with at least 150 minutes of moderate or 75 minutes of vigorous exercise per week, which can accelerate glymphatic clearance and reduce amyloid-beta accumulation.

• Managing chronic stress, as it can negatively impact glymphatic function and accelerate amyloid-beta accumulation.

These interventions primarily work by enhancing glymphatic system function, reducing inflammation, and promoting the clearance of harmful proteins like amyloid-beta from the brain. The easiest one seems to be sleeping!

Regardless of position, prioritizing overall sleep quality by maintaining a consistent sleep schedule, creating a comfortable sleep environment, and practicing relaxation techniques is worthwhile. Of course I wrote a post about that already ;)

Limitations and Future Research

While the current research is promising, it's important to note some limitations and areas for future study:

• Human studies: Most of the research on sleep position and brain waste clearance has been conducted on animals. More studies on humans are needed to confirm these findings and their applicability to human brain health.

• Long-term effects: Research is needed to determine the long-term impact of sleep position on neurodegenerative disease risk and progression.

• Individual variations: Factors such as age, health conditions, and personal comfort may influence the optimal sleep position for each individual.

• Practical considerations: Developing methods to accurately track sleep position outside of laboratory settings will be crucial for further research and practical applications.

Take Home Points

The emerging research on sleep position and brain waste clearance offers an intriguing new perspective on the importance of how we sleep, not just how much we sleep. The potential benefits of side sleeping for brain health add another dimension to our understanding of sleep's role in maintaining cognitive function and potentially reducing the risk of neurodegenerative diseases. More study is needed, and I’ll stop way short of making any quack promises. But the fact that most of us prefer to sleep on our sides, and that most of us spend more time sleeping in that position naturally, must add up to something. Cheetahs would agree.

Ultimately, while sleep position is an important consideration, it should be viewed as part of a holistic approach to sleep health. Prioritizing overall sleep quality, maintaining consistent sleep patterns, and addressing any sleep disorders remain fundamental. Good food, exercise, and stress reduction never go out of style, and we keep finding new mechanisms by which they help. And if sleeping on our backs with a CPAP mask facilitates better, undisturbed, deep, stage 3 and 4 sleep without hypopneas, micro-arousals, or pain - then by all means this is much superior to fretting about side sleeping while obsessively rolling over in bed.