September 2026 letter - Vagus nerve

The vagus nerve is part of the autonomic nervous system, which comprises both parasympathetic and sympathetic divisions. The sympathetic division increases arousal, energy levels, heart rate, blood pressure, and respiratory rate. The parasympathetic division promotes recovery and relaxation, calming various bodily processes—including blood pressure and heart rate—and regulates digestive function.

As the primary nerve of the parasympathetic nervous system, the vagus nerve regulates numerous bodily functions. It is one of the 12 pairs of cranial nerves and arguably the most complex among them. It is the body's longest nerve, connecting the nervous system to many vital tissues and organs, such as the heart, stomach, and intestines. Originating in the brainstem, the vagus nerve branches out and travels through the neck, chest, and abdomen. It establishes a vital link between the brain and the digestive tract, transmitting information about the state of internal organs—including the gut—to the brain.

Functions of the vagus nerve

• Communication between the brain and the gut (gut-brain axis): The vagus nerve facilitates continuous communication between the gut microbiome and the brain. This connection influences mood, appetite, and even decision-making abilities. The vagus nerve regulates the production of digestive enzymes and stomach acid, as well as the contractions of intestinal muscles that ensure motility. Emotions also play a significant role in this process; positive emotions enhance vagus nerve activity, promoting relaxation. Heart function and breathing slow down, yet the process also supports digestion. Stress disrupts digestion and leads to related problems.

• Relaxation and heart health: As mentioned above, the vagus nerve slows the heart rate and lowers blood pressure. High activity is often associated with high heart rate variability (HRV), which indicates good stress resilience and heart health. Low HRV is a negative sign; it makes regulating emotions and stress difficult and can also signal an impending heart attack.

• Reducing inflammation: The vagus nerve is one of several nerves that regulate the immune system, sending anti-inflammatory signals throughout the body. This also aids the body's recovery from inflammation.

Polyvagal Theory

In the 1990s, neuroscientist Stephen W. Porges introduced the polyvagal theory, which examines how the vagus nerve influences our ability to connect and communicate with one another. It divides the autonomic nervous system into three components linked to social behavior and relationships. These components govern autonomic responses that lead to social engagement, a "fight-or-flight" state (mobilisation), or a shutdown (immobilisation) response. The theory has been particularly useful in the treatment of emotional trauma.

The theory explains the physiological mechanisms that enable us to form safe connections with other people. The vagus nerve splits into two distinct branches: the ventral vagal branch (associated with the front/ventral side) and the dorsal vagal branch (associated with the back/dorsal side). The ventral (abdominal-side) branch of the vagus nerve, in particular, plays a role—through a complex process—in how we connect and communicate with others. It becomes active when we feel safe.

Each of these components has a distinct effect on our body and sense of self. When our environment feels safe, the ventral vagal branch is active; we feel connected to others and experience a sense of positivity, relaxation, and the freedom to be ourselves and express our emotions in social situations. We appear energetic and self-confident. Internally, our heart rate calms, and we breathe freely.

When we experience stress or perceive our environment as dangerous, we feel overwhelmed and unsafe, triggering the sympathetic nervous system—the "fight-or-flight" mechanism. Heart rate and breathing accelerate, blood flow to the muscles in the limbs increases, and glucose is released to fuel the muscles. Stress hormones, such as cortisol, are released into the bloodstream.

If stress becomes chronic—turning the stress response into a constant state where a person feels unsafe—they may reach a point of paralysis or "shutdown," becoming apathetic as the dorsal (back-side) branch of the vagus nerve activates. At this stage, many of the aforementioned processes are deactivated, diminishing the ability to engage with the world or maintain social relationships. The person becomes burnt out and exhausted. These feelings include depression, apathy, sadness, and low energy levels.

All these effects are linked to environmental safety or danger, as well as the internal interplay between one's current environment, past life situations, and memories. If a traumatic event has occurred—shattering one's sense of safety—current life events can constantly trigger that internal experience, leading to an automatic reaction.

Everyone has experienced some form of trauma in early childhood. Any event—even one that seemed minor at the time—can have caused great fear, confusion, or a sense of insecurity. These experiences can remain in our nervous system and resurface in various situations later in life. These experiences subconsciously guide our reactions; a seemingly trivial situation might trigger a reaction that feels disproportionate due to past experiences.

Activating the ventral branch of the vagus nerve helps with relaxation and restoring a sense of safety. There are many ways to do this; one of the easiest is diaphragmatic breathing exercises.

Touch is also effective, so many treatments—such as massage or the Havening technique—can be highly beneficial.

How to stimulate the vagus nerve

Stimulating the vagus nerve increases its activity, thereby having a significantly positive effect on bodily functions.

• Cold exposure. Brief exposure to cold stimulates the vagus nerve. Winter swimmers know how relaxing and pleasant it feels to take a dip in icy water. Cold exposure can also be achieved in other ways—for example, by splashing cold water on your face and wrists, taking a quick cold shower, or applying a cold, damp towel to your neck.

• Deep breathing/breathing exercises

• Meditation

• Singing. Singing or humming activates the vocal cords and the muscles at the back of the throat, which are connected to the vagus nerve.

Of course, it is very important to eat healthy, nutritious food and to avoid sugar and various stimulants, such as excessive coffee and energy drinks. Recommended supplements include those important for nervous system function, especially B vitamins (including B12, B1, B2, B3, and B6), vitamin C, and magnesium. Ashwagandha is also recommended for calming the nervous system.

It is also beneficial to try to identify specific, clear stressors in your life and work on addressing or eliminating them.