, sThe role of sleep in digestion

Sleep plays a significant role in digestion, although it may not be immediately apparent. The connection between sleep and digestion is complex and multifaceted, with various physiological processes at play. Sleep is regulated by circadian rhythm which is also known as the body clock. The digestive system is also regulated by the circadian rhythm, which is why individuals often feel hungry at the same time each day.

Rest and restoration

Sleep is very important for the body to repair, rejuvenate, and reset. The deep stages of sleep are particularly vital. During this time, the organs, tissues, and cells that make up the digestive system can not only take a rest but also undergo repair. During deep sleep, the body prioritises cellular repair and growth. This includes repairing the cells lining the digestive tract, which are subject to wear and tear due to the constant exposure to food particles and digestive juices. Deep sleep allows these cells to regenerate, maintaining the integrity of the gastrointestinal lining which improves digestion.

Deep sleep helps strengthen the immune system, which is important for the digestive system as it has its own specialised immune cells that are activated by the beneficial bacteria in the gut. These immune cells protect the gut and digestive system against harmful microbes.

The organs of the digestive system play an important part in the detoxification process by helping to eliminate waste and harmful substances. Deep sleep supports this by helping the liver and kidneys work more efficiently.

Gut Motility

An important part of digestion is the efficient movement of food and waste through the digestive tract. This process, known as gut motility, changes somewhat during sleep. During sleep, whether deep or light sleep, the speed of gut motility is significantly reduced. This slowdown is a necessary adaptation during which the digestive system conserves energy, which is redirected towards the repair of digestive tissues. This enables digestion to be more efficient during waking hours.

The migrating motor complex is a pattern of contractions that occurs in cycles when an individual is not eating. That includes periods of deliberate fasting and sleep, when fasting occurs automatically. This cycle is an important aspect of gut motility that sweeps food particles and debris that remain in the digestive system. This cleaning of the digestive tract helps reduce the likelihood of bacterial overgrowth and maintain a healthy gut environment. The migrating motor complex is most active overnight, when the individual is both fasting and asleep. This highlights how important sleep is for the overall health of the digestive system.

As you wake up in the morning, gut motility gradually increases. This prepares the digestive system so that it is ready to process and digest food. It can also trigger the first bowel movement of the day, showing that the relationship between sleep and gut motility is a finely tuned process.

Hormone Regulation

Ghrelin stimulates the appetite and is therefore often referred to as the hunger hormone. On the opposite side of the coin is leptin, which lets the brain know that the stomach is full, which stops the individual from eating more. For this reason, this hormone is known as the satiety hormone. These hormones can be negatively affected by not getting enough sleep.

Even one bad night’s sleep can affect digestion by causing an increase in ghrelin. This not only increases appetite but can also lead to cravings for carbohydrates. This feeling is often described as ‘hangry’. To make matters worse leptin levels fall after not sleeping very well, so the signal to stop eating is disrupted. This creates a perfect storm with the individual not only overeating, but potentially eating unhealthy foods along with not knowing when to stop eating. The occasional poor night’s sleep does not cause too much damage. However, if the individual suffers from chronic insomnia, it can cause inflammation in the gut which can lead to significant digestive issues including liver disorders, gastroesophageal reflux disease, inflammatory bowel disease, and even colorectal cancer, as well as weight gain.

Disrupted sleep

When sleep is disrupted, this can also lead to digestive issues. Sleep disruption caused by working shifts, especially night shifts, and jet lag can disrupt sleep and knock the body clock out of whack. Likewise, eating late at night or irregularly can also have a negative impact on sleep. The circadian rhythm of sleep is controlled by natural sunlight.

Unfortunately, in today’s age of technology, we tend to live most of the daylight hours indoors, so the link to being outside and the benefits of daylight are being replaced by exposure to blue light waves from laptops, televisions, mobile phones, and electric light. This can disrupt the sleep cycle and sleep patterns, especially if exposure to these light sources is immediately before bedtime.

The cumulative effect of one or more of these factors can cause diarrhoea, ulcers, inflammatory bowel disease, or impact the delicate balance between beneficial and pathogenic bacteria in the gut. It can also cause damage to the lining of the gut.

Microbiome Health

The microbiome is the name for the trillions of microbes collected in the gut. These primarily include beneficial bacteria, known as probiotics. But it also includes viruses, fungal cells, and even some pathogenic bacteria. These microbes play a very important part in overall health as well as digestive health. They not only boost the immune system but also aid digestion, making some vitamins, enzymes, hormones, and amino acids. Emerging research has shown that another way that the microbiome benefits human health is through the link with sleep. This is due to disrupted sleep or chronic insomnia, which can influence the balance of the microbes, which can impact digestive health and overall well-being.

Interplay between the microbiome and sleep

However, the link is multifaceted and incredibly complicated, with poor sleep impacting the microbiome and the health of the microbiome affecting sleep. To try and get to the bottom of this complicated interplay between sleep and the microbiome, one study found that a high number of specific types of bacterial cells in the gut, as well as a good mixture of those different types, has been linked with getting to sleep quickly, how often an individual wakes, how often they wake during the night, and how beneficial sleep is. While it is not possible to discuss all the findings in this article, the takeaway point is that having plenty of beneficial bacteria and incorporating a rich diversity of bacteria in the gut has the best outcomes for sleep, digestion, and overall good health.

Stress, sleep and digestion

A common casualty of stress and anxiety is poor sleep. Likewise, these mental health conditions can also affect the physical health and function of the digestive system. This can affect gut motility and cause indigestion, ulcers, and irritable bowel syndrome. One reason that stress affects digestion is due to the action of the so-called stress hormone, cortisol.

Cortisol

When cortisol is present, it causes the body to react by going into fight or flight mode. Amongst other reactions, one thing that happens is that blood flow is redirected to the heart, brain, lungs, and muscles in the limbs and away from the digestive system. This enables the individual to either fight or run away from whatever is causing the danger and acute stress. In prehistoric times, this would have been a predator.

However, these days, stress is caused by less life-threatening issues, such as paying bills, workloads, or not getting enough sleep. Redirecting blood flow as described is great if you need to run away from an animal that is likely to eat you, as blood flow will return to normal once the danger has passed. However, when chronically stressed in these modern times, the digestive system can suffer, especially gut motility, leading to constipation, diarrhoea, indigestion, gas, and bloating. Having stress management strategies in place to keep stress at bay is important for gut health and sleep alike.

Getting plenty of sleep is vital for a healthy digestive system with sleep and digestion being intrinsically linked. Therefore, prioritising good sleep hygiene is well worth doing. This involves minimising exposure to blue light from electronic gadgets, going to bed and getting up at the same time, sleeping in a cool, dark room, not eating within two hours of bedtime, and getting out in natural daylight during the day, especially first thing in the morning.