Sleep and the Gut-Brain Axis - The Apeiron Life Perspective

7 min read

What it is:

What we do while we’re awake has a profound impact on our gut. Food, movement, and daily stressors are just some of the interactions our body must coordinate throughout the day. The gut is highly sensitive to the environment around us and is often referred to as “the second brain” for good reason. A complex communication network shuttles information along the gut-brain axis to serve a plethora of our most vital processes. The vagus nerve provides a fast-track neuronal highway between the two, while a variety of peptides, hormones, and immune cells communicate via the bloodstream.

The gut is also teeming with microorganisms—about 100 trillion of them. More than 1,000 species of bacteria, archaea, viruses, and fungi help us digest our meals and produce numerous compounds that can either help or hinder our health, depending on which organisms are running the show.

Sleep is essential for maintaining a healthy gut. Both adequate sleep duration (7-9 hours per night) and consistently well-timed sleep (during the biological night) are required to prevent systemic inflammation and allow the gut to perform essential “housekeeping” processes that may prevent diseases, such as cancer and even poor mental health, from developing.

The purported claims:

Healthy sleep helps regulate:

Appetite and satiety signaling
A healthy and diverse gut microbiota
Essential “housekeeping” processes that clear out residual undigested materials
Healthy melatonin production, which is a crucial antioxidant

What the science says:

Digestive System 101

The purpose of the digestive system is to provide the body with the nutrients it needs to survive, grow, and repair. In humans, the digestive system is essentially one continuous tube organized into various compartments separated by sphincters that open and close as needed.

Food is first chewed in the mouth, then swallowed, where it passes through the first sphincter into the stomach. This is where the bulk of the breakdown happens through the action of stomach acid and enzymes. Once the food has been sufficiently reduced into a semi-liquid state, these contents pass through a second sphincter into the small intestine. Peristalsis forces the food along about 20 feet of specialized cells that further digest the food, while others facilitate nutrient absorption into the bloodstream.

Eventually, whatever remains passes through another sphincter into the large intestine, where water is maximally absorbed. Here, a large population of microorganisms feeds off the remaining fibrous content to release essential nutrients that the body would not otherwise have access to. The stool that eventually passes is comprised of any undigested materials and up to 50% bacterial biomass.

Hunger Signaling

Many factors can disrupt what sounds like a relatively straightforward process, and insufficient sleep is one of them. Many studies have shown that sleep-deprived individuals are hungrier the next day and tend to reach for highly palatable, calorie-heavy foods high in saturated fats and sugar. This is thought to happen due to impaired function in the prefrontal cortex, the area of the brain responsible for reasoned decision-making. Instead, more volatile, reward-driven brain areas - such as the amygdala - amp up behaviors that offer immediate “feel good” results, such as satisfying a craving with a tasty treat.

Sleep loss can also change hunger and satiety hormone signaling, causing the stomach to pump out more “please feed me” ghrelin and decreasing the action of “I’m full and satisfied” leptin. This makes us feel hungrier than we are, which over time, can lead us to consume more calories than we need and contribute to the development of obesity.

Inflammation & The Gut Microbiome

Complex carbohydrates (such as whole grains, vegetables, and legumes) are fiber-rich, which gut bacteria love to munch on. The fed bacteria produce beneficial metabolites such as short chain fatty acids (SCFAs), which have anti-inflammatory properties.

SCFAs serve many essential functions, such as maintaining a healthy intestinal cell barrier. They can prevent toxins from leaking from the gut into the bloodstream, where they may alert our immune system and produce inflammation. There is also good evidence that SCFAs help with whole-body glucose homeostasis, fat metabolism, satiety signaling and are associated with better sleep. Both consistent meal and sleep times have shown to produce better health and mood outcomes.

Bacteroidetes and Firmicutes are two of the most common gut phyla, accounting for about 90% of species. When Bacteroidetes is proportionally greater than Firmicutes, there is generally increased SCFA production, a healthy intestinal cell barrier, and less inflammation. But in cases of sleep loss, or other stressors that drive inflammation, the proportion of Firmicutes species can increase. When the balance skews in this direction, these bacteria can produce toxic compounds associated with worse mental and physical health.

Everyone has a unique microbiome that is influenced by multiple areas of life including but not limited to:

Whether you were birthed vaginally or through cesarean section
Breastfed or bottle weaned
Where you were raised
Whether you had pets
If you smoke
The stress you experience
How many times you've taken antibiotics

There is also good evidence that diets rich in prebiotics are good for gut health and sleep. Prebiotics are the foodstuffs that the organisms ferment once they reach the colon and include complex, high-fiber foods. These foods are common in a Mediterranean-style diet and are associated with better mood, cognition, and sleep quality in adults.

Antibiotics have been shown to increase sleep fragmentation in mice, particularly during non-rapid eye movement sleep (NREM) stages. Given that sleep loss is known to be associated with gut dysbiosis, antibiotics may exacerbate the problem. So although sometimes necessary, be wary of antibiotics' effect on the microbiome.

Research shows those with sleep disorders are more likely to have an unhealthy gut microbiome. Obstructive sleep apnea (OSA) is associated with worse cardiovascular health outcomes, and this could be at least partially mediated by the gut microbiome. Approximately 50% of those with OSA have hypertension, and changes in gut bacteria may cause it. OSA is characterized by shallow breathing or breath holds during sleep. This causes intermittent hypoxia, or blood oxygen levels that are too low. Intermittent hypoxia increases inflammation, which is known to degrade the gut lining. But those dips in blood oxygen may also activate processes that increase cell proliferation, increasing the risk of cancer in the long term. By contrast, SCFAs produced by good bacteria promote vasodilation and decrease blood pressure.

Essential Housekeeping Function

Colorectal cancer is the third most common type of cancer in men and the second most common among women. There is an elevated risk of colorectal cancer among those with sleep disorders. There are many other risk factors for cancer, such as poor diet and obesity, but given that sleep can disrupt many important metabolic processes that, in turn, lead to obesity, prioritizing healthy sleep is essential for minimizing cancer risk.

During periods between meals, the "migratory motor complex" is activated in the gut. This gut-sweeping action clears out undigested materials that can otherwise promote inflammation. As sleep is the most prolonged period of rest, a proposed theory is that the "cleaning" process occurs most efficiently during this time.

Irritable Bowel Syndrome and Melatonin

Chronic inflammation of the intestine, pain, bloating, diarrhea, anxiety, and even skin or eye irritations are reported by those who experience irritable bowel syndrome (IBS). Women are about five times more likely to experience IBS than men, and while there is some degree of heredity, IBS

can be influenced bymany factors. Lifestyle, diet, environmental pollutants, hormonal birth control use, antibiotics, and stress can all pile on to create inflammatory issues.

Many people with IBS also have a sleep disorder, and melatonin may be an effective treatment for alleviating symptoms. Melatonin is a potent antioxidant that combats oxidative stress. It is released at night, triggered by the onset of darkness, and exposure to blue light wavelengths can disrupt its release.

Interestingly, data shows that exposure to bright light in the morning may be just as crucial for healthy melatonin production at night as avoiding light exposure in the evening. This is because our circadian rhythms require morning light exposure to release sufficient melatonin at night.

Melatonin production is also affected by the gut microbiome. Melatonin synthesis requires the ingestion of the amino acid tryptophan, which is converted to serotonin and then eventually melatonin through a series of carefully-controlled steps. Some gut bacteria can mop up that tryptophan, decreasing the body’s reserve. However, other organisms can counteract this by synthesizing tryptophan from enzymes such as tryptophan synthase.

A healthy nightly dose of melatonin is essential for countless processes in the body. Melatonin tackles inflammation, decreases blood pressure, and helps us fall and stay asleep. Chronic suppression of melatonin, such as through night shiftwork, insufficient time outdoors, or exposure to too much bright light at night, has implications for health and disease. Cancer risk is significantly higher among night shift workers, and insufficient melatonin may have a large part to play in it.

Our take:

New reasons to prioritize sleep are published each week, and when it comes to gut health, the evidence is abundantly clear: getting enough sleep at night matters. When we veer off course and get a few nights of bad sleep, we change our physiology. If left unchecked, this can cause all kinds of diseases. But we are also remarkably resilient. Slowing down and getting back to basics can help us maintain our health.

Nutritious meals, regular exercise, and mindfulness practices that allow us to activate our parasympathetic nervous system and tap into relaxation can all help contribute to better sleep and overall health.

Will this benefit you?

When we don’t get enough sleep, our mood and cognition suffer. This can amplify the severity of minor problems, pain, and even impair our decision-making. Prioritizing sleep as often as possible is a potent disease preventative and may increase longevity.

Still curious to try it? If you do, here’s what to keep an eye on:

Speak to your doctor if you are struggling with IBS or other gut symptoms. But a small place to start is by gradually increasing your consumption of fermented foods rich in probiotics and complex, high-fiber prebiotics to keep them fed.

Aim to finish your last meal of the day about 3 hours before your targeted bedtime so your body can digest and prepare for its rest state. Most people find that eating too close to bedtime leads to indigestion and worse sleep quality.

Lastly, if you are struggling with your sleep or suspect you might have a sleep disorder, speak with your doctor, who can refer you to a specialist.

References and additional materials:

Peter Attia & Mike Gershon - The Gut-Brain Connection - https://peterattiamd.com/michaelgershon/

Food desire and sleep - https://pubmed.ncbi.nlm.nih.gov/23922121/

Food desire and sleep II - https://pubmed.ncbi.nlm.nih.gov/23814334/

Sugar and inflammation - https://pubmed.ncbi.nlm.nih.gov/29757229/

SCFA and health - https://pubmed.ncbi.nlm.nih.gov/26963409/

Antibiotics and the gut microbiome - https://www.the-scientist.com/news-opinion/what-happens-to-the-gut-microbiome-after-taking-antibiotics-69970

Microbiome stabilizes circadian rhythms in the gut - https://pubmed.ncbi.nlm.nih.gov/36689661/

Sleep, circadian rhythms, and gut microbiome - https://pubmed.ncbi.nlm.nih.gov/32668369/

Antibiotics and NREM sleep - https://pubmed.ncbi.nlm.nih.gov/33177599/

Sleep apnea gut microbiome - https://pubmed.ncbi.nlm.nih.gov/30957979/