What is the vagus nerve?
The vagus nerve, or wandering nerve, is the longest nerve in the autonomic nervous system and runs from the brain to the intestines, branching out to many organs in the chest and abdomen. It plays an important role in digestion by modulating stress, carrying out functions of the Parasympathetic Nervous System (PNS) as it activate the “rest and digest” (or de-stress) mode. In other words, the vagus nerve helps the body transition between a state of stress to non-stress, including associated bodily functions.
The vagus nerve represents the primary communication pathway of the gut-brain axis: the gut constantly sends signals to the brain and vice-versa, in the form of neurotransmitters, linking our microbiome and our emotions.
Key Neurotransmitters:
Gamma-aminobutyric acid (GABA) and acetylcholine are the two important neurotransmitters that excite or activate the nerves in the gut to stimulate the PNS (non-stress), turning off the SNS (stress), slowing down heart rate and increasing blood flow to the gut, promoting gut motility. Stress induces inflammation so a healthy vagus nerve that can produce the necessary neurotransmitters helps to regulate it: GABA is known as an inhibitory neurotransmitter that suppresses the sympathetic/stress response as it decreases pro-inflammatory cytokines while releasing acetylcholine to “rest and digest”. All this communication occurs via the vagus nerve, so it’s important to keep it healthy and resilient.
How do we know whether we have a resilient vagus nerve?
By assessing our vagal tone: it shows how well a person’s vagus nerve is functioning. We can either have a high vagal tone or a low vagal tone.
A high vagal tone is characterized by demonstrating resilience to stress, means our body can manage it pretty well and we can easily transition to a non-stress state. With a high vagal tone have a general sense of wellbeing, healthy appetite and bowel movements, a healthy gut, a good heart rate and heart rate variability, which measure the body’s ability to transition from stress to rest and digest. A slower heart rate and increased variability (measure of the variation in time between each heartbeat) shows a high vagal tone, so a healthy vagus nerve. At the contrary, the more stressed a person is, the faster the heart beat and shorter the time between each beat, which characterizes a low vagal tone. In addition, low vagal tone shows up with chronic fatigue, lack of motivation, feelings of depression, anxiety and loneliness, unhealthy gut, bloating, IBS symptoms, elevated heart rate and blood pressure, and inflammation.
Chronic stress and low vagal tone affect physical and mental health:
Under chronic stress and low vagal tone, and a lower ability to transition to a non- stress state (PNS), the vagus nerve is not able to release the necessary neurotransmitters that promote an anti-inflammatory response, which leads to chronic inflammation, including inflammation in the gut. This create a situation where the vagus nerve is cut, the gut-brain communication is impaired, giving rise to gut conditions such as leaky gut syndrome and its cascading health effects, colitis and IBS symptoms. The connection between chronic stress/low vagal tone and chronic inflammation can also explain why many gut conditions are often coupled with depression, anxiety and other mood disorders: the vagus nerve in the gut-brain axis don’t only use GABA and acetylcholine to communicate, but also serotonin, dopamine and norepinephrine, which become inhibited under chronic stress and inflammation, as distress signals are excessively sent by the vagus nerve via the gut-brain axis. That’s why it is critical to learn how to manage and regulate our nervous system to avoid the long-term ill effects of stress on the body and mind.
Other interesting functions of the vagus nerve:
The vagus nerve is able to regulate appetite:
The vagus nerve is able to regulate appetite by telling the brain when we are full or hungry: distension of the stomach activates receptors that send signals back up to the brain to produce the satiety hormone, leptin, activating the feeling of being full. Similarly it is the main pathway that ghrelin, the hunger hormone uses when blood sugar gets low, triggering the feeling of physical hunger. Through the vagus nerve, insulin is then released from the pancreas after a meal to manage blood sugar, pointing to a direct role in blood sugar modulation. There is also a strong correlation between our stress level, vagal tone, inflammation and weight management: the more stressed, the more inflamed and the higher the risks of obesity.
The vagus nerve also affects nutrient absorption and can impair our vitamin B12 intake:
The vagus nerve also affects nutrient absorption and can impair our vitamin B12 intake. A healthy vagal tone promotes the shift to rest and digest and enables the digestion to function as it should: B12 binds to the protein in the food we eat, once in the stomach under healthy digestion, hydrochloric acid and enzymes unbind B12 into its free form, and then combine with a protein called intrinsic factor so that it can be absorbed further down in the small intestine. Under an over-activated nervous system, digestion doesn’t occur as it should, gut issues rise and B12 absorption in impaired. On the long-term, B12 deficiency can cause a multitude of illness symptoms, from physical, to neurological and psychiatric disorders. Low B12 and folate levels hinders the production of serotonin and dopamine, which impacts our emotional and mental health. Individuals with a MTHFR genetic mutation where the body cannot produce enough folate, are even more at risk and supplementation is strongly advised.
7 ways to naturally stimulate the vagus nerve:
There are exercises and practice to maintain a healthy vagus nerve for optimal gut and overall health:
- Deep belly breathing: it slows down heart rate and increases heart rate variability. Extended exhales especially stimulate the vagus nerve. (short and shallow breathing keeps the body in a state of stress).
- Alternate nostril or pranayama breathing.
- Cultivate positive emotions: when we have positive, happy thoughts, oxytocin and dopamine are released while bad thoughts and negative self-talk triggers stress within the body and the mind. Emotional regulation and inflammation are connected.
- Meditation: one of the most powerful tool to promote a healthy mind and stress reduction.
- Laughter, positive sounds, humming, singing and overall wellbeing stimulate the production of GABA.
- Gentle movements such as tai chi and yoga, especially inversions, back bends and sun salutation are particularly good to stimulate the vagus nerve.
- Cold plunges, cold showers increase resiliency to stress.
A healthy vagus nerve promotes resilience in the body and overall wellbeing. It’s the communication line of the gut-brain axis and a strong bridge between these two control systems is a powerful tool for gut and holistic health.