In one of our previous articles, we talked about how poor gut health can make us more fatigued throughout the day. We also shared about how gut health is connected to the brain through the gut-brain axis, and that the bacteria living in your gut can affect your mood, emotions, and even thinking.
With these concepts in mind, you can imagine that gut health also influences our sleeping patterns. Turns out, sleep and the gut microbiome are intricately linked and can affect one another in fascinating ways. Maybe grandma was right to tell us not to eat before bedtime.
Let’s further explore the relationship between gut health and sleep.
Sleep and the Gut-Brain-Microbiome Axis
Researchers are discovering that sleep has an enormous impact on what is known as the gut-brain-microbiome axis, which is the communication line between the brain, gastrointestinal system, and the microorganisms living in our bodies. Studies are showing that the relationship between sleep and these systems works in both directions. People who sleep poorly can experience changes to their gut microbiome, decreasing the diversity of bacteria species and increasing the number of ‘bad’ bacteria that can cause gut inflammation. Poor sleep also negatively affects the populations of ‘good’ bacteria that produce important metabolites such as short-chain fatty acids (SCFAs), which help reduce gastrointestinal inflammation. There’s evidence that one of these SCFAs, known as butyrate, also enhances sleep.
The gut microbiome can impact sleep as well. In a study using Drosophila flies, a common model organism used in research, scientists studied the effect of sterilizing the gut microbiome of the flies and compared them to normal flies. They discovered that the sterilized flies required much longer sleep and struggled to rebound after a bout of sleep deprivation. In another study involving young adults, researchers found that individuals that report better sleep quality had a higher abundance of two bacterial genuses, Blautia and Ruminococcus, versus those who had poorer sleep quality.
The Role of Cytokines
Cytokines are messenger proteins released by cells to tell their neighbors how to respond to a threat to the immune system. Some cytokines increase inflammation while others decrease it to signal that the inflammatory response isn’t needed any longer. The gastrointestinal system is connected to the immune system as there are many pathogenic bacteria species that live in the gut, so the body is constantly fighting off any potential infection. However, changes to the bacterial composition of the gut can lead to the release of pro-inflammatory cytokines that are meant to alert the immune system to respond but can result in other unintended side effects.
A perfect example is the two cytokines, interleukin-6, and interleukin-beta. These two cytokines are responsible for increasing inflammation during infection and tissue injury. Thanks to these cytokines, a bump on the head lead to swelling and a bout of strep throat leads to swollen tonsils, which ultimately lead to increased blood flow, clearance of damaged tissue, and healing.
The trouble is that these two cytokines are also involved in the physiology of sleep. Known as somatogenic cytokines, these two molecules increase sleepiness when their blood concentration is high. Studies have shown that administration of interleukin-beta results in spontaneously drowsiness and fatigue, and its levels increase with higher amounts of sleep loss. And low levels of inflammation coming from pathogenic bacteria trying to invade the body through the gastrointestinal lining can cause an elevation in interleukin-6 and interleukin-beta.
On the other hand, sleep deprivation can increase the presence of these cytokines, leading to stress and inflammation of the gut. Plus, certain genes involved in controlling the circadian rhythm can influence the composition of the gut microbiome. Sleep and gut health play off one another and can induce a vicious cycle when an individual is in poor health.
Bacteria Need Sleep, Too
The bacteria that live in the gut have their own circadian rhythm. While changes in the gut microbiome populations over the short term are small and can be rather resilient over months and years, these fluctuations are still important for overall health. Sleep appears to help certain bacteria populations thrive while others die off. When individuals change their sleep patterns or eat during abnormal hours, these population changes can result in metabolic conditions like obesity or diabetes.
Feeding schedules are a large factor in these patterns. When mice were subjected to ‘jet lag’ and fed at strange hours, they experienced significant changes to their metabolism such as elevated fatty acids, glucose, and triglycerides levels. Researchers believe that sleep provides an opportunity for certain bacteria that rely on immediate daytime feeding to die off, while more resilient bacteria that can feed on the more difficult-to-digest nutrients remain stable. The presence of high-calorie foods during sleeping hours can upset the microbial balance and lead to chronic diseases over time.
Sleep is one of the most important biological functions universal to all organisms, including humans. While our globally-connected, industrialized world can sometimes push sleep to the corner, we forget the powerful evolutionary patterns and connections between our human physiology and our gastrointestinal bacteria forged over millions of years. So before taking another bite of that midnight snack, you may want to think twice about the bacteria sleeping quietly in your gut.