How Bacteria influence our sleep

The human body needs to regularly recover during sleep. But sleep is much more than just the relaxation of the muscles, the initiation of regeneration processes and the processing of impressions in our dreams. It is an essential part of our lives and is influenced by our bacteria.

The little brother of death

Even in Greek mythology, sleep was referred to as the little brother of death. This was not so much to emphasize a danger as to emphasize its importance for the body. In mythology, Hypnos (the god of sleep) and Thanatos (the god of death) are brothers, both children of Nyx, the goddess of the night. This connection led to the idea that sleep resembles death and is thus like a “little brother” of death. However, this comparison is not so much about a possible “deadly” danger as about the fact that both conditions imply a form of unconsciousness or a different level of consciousness.

Plato referred to death as the final transition of the soul, while sleep was understood as a temporary loss of consciousness. Even though the Greek philosopher used this comparison to explain the immortality of the soul and the cycle of life and death, he emphasized the enormous importance of sleep for humans. One possible interpretation according to Plato would be that humans “test out” another world or level of consciousness during sleep without fully turning to it. This “test run” is an essential and necessary part of life.

Melatonin – the power hormone

Modern medicine, which is based on measurable values and studies, takes a somewhat different view. Nevertheless, the enormous importance of sleep, without which survival would not be possible, remains undisputed.

The hormone melatonin plays a key role here. It is a true “power hormone” because it not only promotes sleep but also general health. The hormone plays a central role in controlling the circadian rhythm.

This internal clock is highly dependent on melatonin. It regulates many physiological processes in the body, such as sleep, wakefulness, hormone production and body temperature. The hormone is produced in the pineal gland, a tiny, rice-grain-sized gland in the brain. This in turn is controlled by the suprachiasmatic nucleus, a small brain region connected to the photoreceptors of the eyes. This connection prevents the pituitary gland from producing melatonin during daylight or when exposed to blue light. In the dark, however, the pineal gland is signaled to produce melatonin, which causes drowsiness.

How is melatonin produced?

The important hormone is produced from serotonin, and bacteria play an important role here. They support the production of serotonin. Although the serotonin produced by the bacteria in the gut cannot pass the blood-brain barrier directly, its precursor, the amino acid tryptophan, can. The sequence is as follows:

• The gut microbiome influences the production of tryptophan.
• The tryptophan enters the brain.
• Serotonin is produced in the brain.
• Melatonin is then produced from serotonin in the brain.

The dual function of serotonin

In addition to its function as a precursor of melatonin, serotonin acts as a neurotransmitter in the brain and plays a central role in regulating mood. This is why it is often referred to as the “happy hormone”. In the gut, on the other hand, the serotonin produced by the bacteria aids digestion and influences blood pressure. Serotonin therefore has a dual function, depending on where it is produced or released.

The role of bacteria for sleep

Bacteria play a crucial role in processes that affect sleep. This once again illustrates that the microbiome should be understood as part of the human being and not just as a collection of bacteria.

First, the bacteria produce substances (short-chain fatty acids) that stimulate human cells in the gut to make serotonin, which in turn can be converted to melatonin.

Second, bacteria affect the amount of tryptophan that is eventually converted to serotonin and further to melatonin. Although the bacteria themselves do not release tryptophan, they can cleverly modulate the amount of tryptophan made in the gut.

Melatonin in the gut can reach the brain through the bloodstream. The blood-brain barrier, which protects the brain from many substances, can be easily penetrated by this small and fat-soluble substance, melatonin. In the brain, it then supplements the melatonin produced there by the pineal gland.

However, a large proportion of the melatonin produced in the gut remains in the gut and regulates digestion, protects the intestinal mucosa and supports the immune system. It also has an antioxidant and anti-inflammatory effect.

Studies thus show that both tryptophan formed in the gut, which is converted into serotonin and melatonin in the brain, and melatonin formed in the gut can be transported to the brain. However, the main production of melatonin takes place in the brain through the pineal gland.

Synchronizing the biological rhythm

Interestingly, the intestinal bacteria have their own rhythm, which is synchronized with the body’s circadian rhythm. If the biological rhythm is disturbed, for example by jet lag or shift work, the microbial populations in the intestine can also become unbalanced, which in turn can affect sleep.

The connections between sleep and bacteria are complex and multifactorial – as is so often the case in the body, not just a single parameter is decisive. Simplification can help to better understand the interactions, but it should always be considered as just that.

The gateway to sleep and death

But back to the pineal gland, which is often referred to as the gateway to sleep and also to death. Its main function is to produce melatonin, but it is also thought to be involved in regulating reproduction, influencing the immune system and even the aging process.

It is one of the central control centers in our body, the guardian of sleep and reproduction, and possibly plays an essential role in the dying process through the formation of DMT (dimethyltryptamine).

It is fascinating that this tiny gland in the brain can communicate directly and indirectly with bacteria.

Plato knew nothing about the existence of the pineal gland or bacteria. But he already realized more than 2,000 years ago that sleep and death are very similar.

The exact role of the pineal gland, especially in death due to the possibly increased production of DMT, is controversial in science. As is so often the case, different worlds collide here: the materialistic, measurement-based medical world and the philosophical world. Both are separate from each other, but there is a bridge that connects them.

Building the bridge

This bridge may come as a surprise to many, but those who cross it open up a new dimension. This bridge is mindfulness.

Through mindfulness, insights can be gained that are excluded by reason from the outset. It enables insights that cannot be achieved by purely evidence-based means. That is the strength of incorporating mindfulness into life.

And as we have seen, there is another world that plays a role in the overall system of life, sleep and death: the world of bacteria.

Only by connecting all these worlds and excluding none can we have a chance of arriving at our origins and understanding ourselves.

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Further reading:

dos Santos, A.; Galiè, S. The Microbiota–Gut–Brain Axis in Metabolic Syndrome and Sleep Disorders: A Systematic Review. Nutrients 2024, 16, 390. https://doi.org/10.3390/nu16030390

Seong HJ, Baek Y, Lee S and Jin H-J (2024) Gut microbiome and metabolic pathways linked to sleep quality. Front. Microbiol. 15:1418773. https://doi: 10.3389/fmicb.2024.1418773