On average, we spend one-third of our life—about 25 years—sleeping. Sleep is an integral part of every day, and yet it eludes many. For others, sleep hasn’t made the priority list. According to the Centers for Disease Control and Prevention, an estimated 35% of U.S. adults do not get enough sleep (CDC 2016). Some 50–70 million people suffer from at least one sleep disorder, with 30 million struggling with insomnia (Institute of Medicine 2006). Sleep aids are a multibillion-dollar market (Consumer Reports 2016).
A lack of sleep brings deeper implications as research finds connections to heart disease, diabetes, obesity, Alzheimer’s, depression and cancer (Cappuccio & Miller 2017; McHill & Wright 2017; Mullington et al. 2009; Vaughn, Rotolo & Roth 2014; Walker 2017).
As sleep scientists dive into the questions of why we sleep, what happens when we do and how it affects our health, the answers are bringing us closer to understanding the extraordinary ways a human being functions. One that fascinates is the gut-sleep connection.
The gut and sleep? There is more to it than munching too many chips while binge-watching a favorite show and then tossing and turning all night. Home to thousands of bacteria that make up the microbiome, the gut affects appetite, metabolism, weight management, and whether or not a sound sleep arrives at night. To understand how nutrition, the gut and sleep interact, take a closer look at the purpose and physiology of sleep. Then discover the intricate web that ties together food and drink, the gut, and the health benefits of sleep.
Why Do We Need to Sleep?
When we hit the pillow at night, we may perceive sleep as a resting period, but for the brain and body, it’s a complex, metabolically active time. All aspects of our being—systems, organs, tissues, mind—are supported or compromised based on how much and how well we sleep. Sleep is designed to restore, recalibrate, renew and upgrade brain and body functions.
From the perspective of the brain, sleep aids in problem-solving, influences memory retention and the ability to concentrate, regulates emotions, improves coping skills, and inspires creativity (Lewis, Knoblich & Poe 2018; Vandekerckhove & Wang 2018). In the body, sleep boosts immunity, balances metabolism and hormones, regulates blood sugar levels, manages blood pressure, combats fatigue, and suppresses cancer cell growth (Ibarra-Coronado et al. 2015; Irwin 2015; Schmid, Hallschmid & Schultes 2015).
The physiological processes behind all of these actions require being asleep. In a growing number of studies, the consensus is that the less we sleep, the higher our rate of diseased states and the shorter our life span. That explains why sleep determines health and quality of life.
What Regulates Sleep?
The two main factors regulating sleep are circadian rhythm and sleep drive. Both of these factors are linked to the gut, specifically the microbiome and the food choices we make. The first is our internal biological clock—called the suprachiasmatic nucleus—which creates our circadian rhythm. This internal rhythm, which has a cycle of roughly 24 hours, helps stimulate wake-sleep periods and is highly influenced by the environment, particularly light exposure. Beyond regulating wakefulness and the desire to sleep, circadian rhythm plays a role in determining body temperature, hormone secretions, metabolic rate, emotional state, appetite and digestive function.
The second is our sleep drive. During our wake cycle, the chemical adenosine is released and acts as a barometer of how long it’s been since we last slept. The chemical accumulates in response to increased energy consumption and metabolic activity from the day’s events. After an average of 12–16 hours of wakefulness, adenosine decreases alertness and eventually brings on a desire to sleep (Bjorness & Green 2009; Huang, Urade & Hayaishi 2011; Walker 2017). The combination of an internal chemistry shift and our circadian rhythm interacting with environmental cues helps regulate the timing of sleep and when we wake the next morning. These factors not only lead to sleep but launch a well-orchestrated sequence of events once it begins.
The Gut-Brain Axis
The gut microbiome communicates with the brain to influence sleep through three pathways: endocrine hormone release, nerve transmission and immune activation.
Endocrine cells of the gut release neurotransmitters such as cortisol, tryptophan and serotonin, which affect the HPA stress axis and communicate with the brain. The intestinal nervous system formfs synaptic connections with the vagus nerve, which directly connects the gut to the brain to create an information transmission highway. The microbiome interacts with immune cells to alter levels of cytokines, immune molecules regulating inflammatory responses in the brain and body. This bidirectional gut-brain communication influences the amount and quality of sleep we experience.
What Happens During Sleep
After waking from a bizarre dream, we sometimes perceive sleep as chaotic and unstructured. The opposite is actually true. Sleep is highly controlled and predictable. Two different types of sleep occur through a total of five stages that repeat every 90 minutes for about five cycles over a full night’s sleep. It is that precise. The two types of sleep are non–rapid eye movement (NREM) and rapid eye moment (REM).
Non–rapid eye movement (NREM) sleep has four stages that take us from light sleep to deep sleep, indicated by slow brain waves, lower pulse and dropped blood pressure. We spend 75% of our sleep time in NREM. NREM plays a role in transferring new information, skills or memories to long-term storage. A part of that process is weeding out unnecessary neural connections so that we remember what we need to and forget what we don’t (McCarley 2007). It’s during the deepest stages of NREM that the body boosts immunity, balances metabolism, regulates blood pressure and repairs muscles/tissues.
Rapid eye moment (REM) sleep, commonly known as the dreaming stage, takes the information transferred during NREM and integrates it with all other existing memories. REM helps make sense of what we learned that day and places it in the context of what we already know. REM is also a time when we have an emotional reset and find resolution with the day’s experiences. This overnight therapy session is what makes it possible to wake level-headed, accurately read social cues and navigate through life’s challenges (Kahn, Sheppes & Sadeh 2013; Nishida et al. 2009). The reason why people experience the bizarre scenarios that can arise in dreams during this stage is because rational thought is deactivated and anything is possible! This is also how sleep inspires creativity and assists us with problem-solving—by helping us get out of our own conscious, sometimes narrow-minded way.
All types and stages of sleep have specific functions benefiting health and well-being. The timing is just as important as the action of sleep. Research demonstrates that the early hours of sleep are dominated by NREM, while the later hours, especially the last 2 hours of an 8-hour sleep night, are dominated by REM (Walker 2017). Sleep stages are experienced every 90 minutes; the ratios simply change. This makes getting a full night’s sleep, aligned with circadian rhythms and without sleep aids, critical to reaping the health benefits of sleep.
What Happens When We’re Sleep Deprived?
A loss of sleep, defined as sleeping less than 7 hours a day, impairs well-being and results in a suboptimal physical and psychological state. Even over a mere 10 days, the brain and body are deeply compromised. (Just imagine what years of insufficient sleep may do.) Sleep deprivation affects our ability to concentrate, learn and remember (Havekes, Vecsey & Abel 2012). It also influences our emotional state by increasing reactivity, mood swings, aggression and hypersensitivities, while creating a fear-based mindset. A lack of sleep literally makes us more animalistic by switching our brain activity from the cortex to primitive brain regions. Forget about problem-solving, brainstorming, insights or creativity. Those are out of reach.
Sleep deprivation also takes its toll on the body. Without enough sleep or enough quality sleep to nurture all sleep stages, renewal, detoxification and enhancement processes are never fully completed. Over time, this leads to compromised immunity, unmanaged inflammation and the onset of diseases and conditions like heart disease, diabetes, obesity, cancer, depression, anxiety, Alzheimer’s, autoimmune illnesses and digestive disorders (Ali et al. 2013; Covassin & Singh 2016; Hsaio et al. 2015; McEwen & Karatsoreos 2015; Mullington et al. 2009; Nagai, Hoshide & Kario 2010).
A major pathway that links sleep to illness is the way circadian rhythms regulate immunity and the corresponding hypothalamic-pituitary-adrenal (HPA) stress axis (Buckley & Schatzberg 2005; Hirotsu, Tufik & Andersen 2015). When we are sleep deprived, the HPA stress axis is activated, resulting in hormone shifts: Cortisol increases, and levels of growth hormone decrease (Besedovky, Lange & Born 2012; Kim, Jeong & Hong 2015; Rea, Dinan & Cryan 2016 ). This compromises immunity, affecting our ability to manage inflammation and fight off infection.
As sleep deprivation keeps the stress axis on high alert, the effects alter metabolic activity, particularly insulin regulation, thereby further suppressing the immune system (Tsai et al. 2018). In conjunction with the hyperactive stress response, the sympathetic nervous system (SNS) remains in a fight-or-flight status. When the SNS stays in an “on” position without balance from the parasympathetic nervous system (PNS), the result is suppression of anti-viral and anti-inflammatory processes and higher susceptibility to disease.
Fortunately, there is good news: We are taken out of the SNS during NREM sleep, and the release of stress chemicals, specifically norepinephrine from the SNS, shuts off during REM sleep (Walker 2017). Sleep helps us manage stress, resolve emotions and wake with a clear head. Since inflammatory and psychological pathways are shared in the body, this in turn affects immunity (Sternberg 2001).
But it doesn’t stop there. The sleep-immunity connection is also intricately linked to the gut.
How Does Gut Health Play a Part?
The gut goes beyond its mechanical role of digesting food and extracting energy. Also known as the enteric nervous system, the gut regulates mood, behavior, emotions and higher cognitive function. As research continues to uncover these connections, we are identifying practical lifestyle actions with the gut as a starting point.
Three aspects of the complex digestive system pertain to the gut-sleep connection.
- The gut has its own brain, nervous system and ability to work independently of the neocortex (rational or thinking) brain. This gut-brain regulates immunity, coordinates neurotransmitter and hormone secretions, influences emotions, affects threshold sensitivity to pain, and supports decision-making and sleep patterns (Liu & Zhu 2018; Rosselot, Hong & Moore 2016; Wu & Wu 2012).
- Seventy percent of the cells that provide our immunity reside in the gut. They’re part of the gut-associated lymphatic tissue, or GALT. Immunity extends past the expected role of a defense system against viruses, bacteria or foreign pathogens. Immunity has a hand in mood, emotions, circadian rhythms and the ability to sleep deeply.
- The Human Microbiome Project has taken an extensive look into the hundred trillion microbes that live throughout the body, with a special focus on the 4 pounds found in the gut. This microbiome, composed of a thousand different types of bacteria, is unique to each one of us. It participates in nutrient absorption, the learning process, immune responses, coping abilities, state of mind and sleep patterns.
The microbiome has its own internal rhythm or clock, just as the body is governed by a circadian rhythm. These two rhythms are intertwined and work together to manage digestion, immunity, brain chemistry and sleep (Voigt et al. 2016; Wang et al. 2017). Each of the different microbes produces specific neurotransmitters, immune cytokines, and metabolites such as serotonin, dopamine, GABA (gamma-aminobutyric acid) and melatonin, all of which influence stages of sleep (Barrett et al. 2012; Li et al. 2018; Petra et al. 2015). When sleep deprivation throws off circadian rhythms, the composition of these microbes changes (Anderson et al. 2017).
Whether sleep deprivation is due to psychological stress, late-night shift work, inflammatory issues, jet lag or simply not making sleep a priority, there’s a direct connection between gut and brain. This connection is bidirectional. If the microbiome is not nurtured properly through eating and lifestyle actions, the change in microbe composition can initiate sleep deprivation. It works both ways (see “The Gut-Sleep Cycle,” left).
Sleep Manages Appetite and Metabolism
Exploring the gut-sleep connection is another way to appreciate the holistic design of a human being. Everything about us is connected. How does sleep manage our appetite, metabolism and long-term weight management? It comes down to hormones.
When we’re sleep-deprived, there is a shift in many of the hormones that stimulate hunger and alter our metabolism. Two key players are ghrelin and leptin. Ghrelin, mainly a digestive hormone, communicates hunger so that we seek our next meal. Ghrelin also plays a role in sleep by promoting the slow waves of deep NREM, the release of growth hormone and the regulation of insulin, which all support nighttime’s healing processes (Kim, Jeong & Hong 2015; Weikel et al. 2003).
Leptin, found in adipose tissue, regulates long-term energy balance and will suppress appetite to maintain a balance between eating and fasting. It communicates satisfaction with a meal, signaling it’s time to stop eating.
When this ghrelin and leptin duo is working effectively, we experience a healthy appetite, feel satisfied from our meals and maintain a fit weight. It’s another story when sleep loss disrupts the actions of these two hormones.
In times of insufficient sleep, ghrelin responds by increasing appetite along with creating sweet cravings, especially for fast-releasing carbohydrates such as bakery goods. When we’re tired, brain functioning shifts to more primitive regions, which affects decision-making. (You will have no problem eating an entire bag of chips or rationalizing a drive-through fast-food meal.) During sleep-deprived moments, leptin, which communicates satisfaction and removes the appetite signal, keeps the green light on. This results in overeating, less health-supportive food choices, eating that is influenced by emotions, and hormone activation that simultaneously slows metabolism and increases fat storage (Klok, Jakobsdittir & Drent 2007; Leproult & Van Cauter 2010; Taheri et al. 2004).
Ghrelin and leptin are the strongest influencers of this sleep-eating connection; however, research is currently bringing additional hormones—such as cortisol, adiponectin, insulin and endocannabinoids—into the conversation. Ultimately, less sleep shifts the entire hormone network to stimulate hunger and create cravings, leaving us unsatisfied and struggling with weight management. Take-home message—make sleep a priority!
Eating Strategies for Improved Sleep
With a bidirectional gut-sleep connection, creating eating strategies to support the microbiome is a starting point for regulating and improving sleep patterns. This can be done through food selection, timing and the eating environment.
Eat a Primarily Plant-Based Diet
This recommendation is based on a few factors. First, plants contain phytonutrients, health-supportive compounds that boost antioxidant capacity and strengthen immunity (Eichelmann et al. 2106; Liu 2013; Tuso 2013). Immunity is one of the three main pathways in the gut-sleep link. Eating a plant-based diet also creates a nutrient profile that is higher in complex carbohydrates and fiber and lower in saturated fats. Research is demonstrating that this combination decreases the number of nighttime arousals and supports longer periods spent in the deep NREM sleep stage (St-Onge, Crawford & Aggarwal 2018; St-Onge et al. 2016). Fiber, along with its immune system–boosting qualities, is a microbiome supporter, feeding friendly bacteria (Menni et al. 2017; Singh et al. 2017).
Researchers are finding that eating a primarily plant-based diet helps to regulate blood sugar levels and stimulate production of the neurotransmitters serotonin and melatonin, thereby calming the nervous system and helping us get to sleep and also stay asleep (Islam et al. 2015; Strasser, Gostner & Fuchs 2016). Brain-calming foods include oats, avocado, walnuts, pumpkin seeds, bananas, tomatoes, plums and seaweeds. As much as the research fascinates with its detail, however, do not overthink or overcomplicate food choices. This can just add additional stress and further affect sleep patterns. Simply shift to eating more plants, fruit, nuts and seeds.
Add Small Amounts of Fermented Foods
The gut-sleep connection is influenced by the number of friendly bacteria as well as the diversity of bacterial strains. This means that adding small amounts of fermented foods to our diet can boost sleep. Raw, unpasteurized, naturally fermented sauerkraut, tempeh, miso and apple cider vinegar are all options.
Minimize Caffeine Consumption
Remember the sleep drive and release of adenosine that regulate sleep? Caffeine, perhaps from a cup of coffee, blocks adenosine cell receptors and halts the communication that regulates the wake-sleep cycle. This temporarily increases dopamine and adrenaline so we feel more alert and motivated. Because caffeine blocks the receptors for adenosine, it accumulates in the bloodstream until the caffeine metabolizes, releasing the chemical process and resulting in an energy crash (Holford 2005).
This cycle of energy burst to exhaustion disrupts sleep. If you struggle with insomnia, avoid caffeine beverages, like coffee, until your sleep improves. Otherwise, drink a morning cup of coffee or other caffeine-infused beverage no less than 10 hours prior to bedtime. Ten hours is how long it takes to metabolize caffeine out of your system. While making this adjustment, pay attention to staying hydrated, as that also influences sleep quality.
Make Dinner the Smallest Meal
It’s never just about the food. Everything about the eating experience affects the absorption and assimilation of nutrients and, more importantly, how food interacts with our entire being—body and mind. One factor is the timing of meals. The body has internal physiological processes and cycles that happen at precise times of the day. Since the digestive system is most active during earlier parts of the day, lunch is ideally the largest meal and dinner the smallest. Consider a soup or snack for dinner no later than 7 p.m. in preparation for the body’s evening healing and restorative processes. This may shift socialization around meals, but that shift can lead to positive sleep patterns and, ultimately, a boost in health.
Add Mindfulness to Your Eating Experiences
Mindfulness alters the activation of the nervous system from SNS to PNS, which supports efficient digestion. Begin with conscious breathing prior to a meal, then eat more slowly with attention. Practicing being present and aware is associated with decreased inflammation and improved sleep (Fountain-Zaragoza & Prakash 2017; Pintado-Cucarella & Rodriguez-Salgado 2016).
Lifestyle Actions for Better Sleep
Particular daytime actions and nighttime routines influence the ability to fall asleep and experience a night of quality, restorative rest.
- Begin and end your day with meditation to help set the tone for the day’s challenges and to decompress as you settle in for the night. A daily meditation practice has been shown to affect the entire being—body and mind. With changes to the brain’s architecture, regulation of the HPA-stress axis and alteration
in hormone secretions, meditation increases slow-wave states of NREM and enhances REM cycles, thereby improving the quality of sleep. There is also a shift from SNS (sympathetic nervous system) to PNS (parasympathetic nervous system) dominance that helps to overcome psychological distress, elevated cardiac activity, higher body temperatures and activation of the brain’s fear centers, such as the amygdala—all of which can contribute to insomnia and sleep-related struggles (Nagendra, Maruthai & Kuffy 2012).
- Exercise! The benefits include boosting immunity, improving cardiorespiratory function, enhancing mood and managing metabolism. All these factors promote quality sleep. Those who exercise regularly have been found to experience longer NREM sleep stages, which is when the majority of nighttime’s healing occurs (Uchida et al. 2012). Although there is conflicting research on how exercise relates to insomnia, try avoiding vigorous activities for at least 3 hours prior to bedtime to
assist the body in transitioning out of a heightened alert
state and beginning to prepare for sleep.
- If you’re struggling with insomnia, wake up and go to bed at the same time every single day, regardless of whether it’s a weekday or weekend day.
- Remove or avoid LED-powered lamps, laptops and television screens prior to bed. They decrease REM sleep and affect melatonin release, disrupting circadian rhythms.
- Don’t fall asleep on the sofa and then drag yourself into bed, as this disrupts the sleep stage sequences. Head to bed when sleepy.
- Make sure the room temperature is a little cooler than daytime temperatures, ideally around 65 degrees Fahrenheit, as core body temperature needs to drop a few degrees to initiate sleep.
- Avoid sleep aids. They do not bring on natural sleep but instead provide a sedative-induced sleep that suppresses the REM stage essential to integrating memories and
resetting emotional state.
- If you need to use an alarm clock, do not press the snooze button. Each time you fall back to sleep to be jolted awake again by the alarm, there is a direct impact to the cardio-vascular and nervous systems. If you practice waking and retiring at the same time, circadian rhythms will help you wake naturally a few minutes prior to your alarm.
Lifestyle Choices and Nutrition Aid the Gut-Sleep Connection
Sleep is a pillar of health and well-being, as it touches all aspects of body and mind. We can begin to improve our quality of sleep, decrease the onset of chronic illnesses and, perhaps, extend our life spans by beginning to nurture the gut-sleep connection. This begins with food choices and mindful eating and extends into our daily actions. The human design is holistic, with every system of the body connected, including the gut-sleep system. Seek out consistency in your eating and sleep routines to reap the benefits.
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