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An Intro to the Vagus Nerve

by Dr. Mitchell Rasmussen, DC, CFMP, FRC-ms

The Vagus Nerve is the tenth cranial nerve (we have twelve). It originates in our brainstem and connects to almost every organ in our thoracic cavity— i.e. heart, lungs, spleen, pancreas, liver, digestive tract.

It belongs in a branch of the peripheral nervous system (everything outside of the brain and spinal cord) that regulates the internal activity of organs and glands— the things we don’t consciously control. Within this context, the primary function of the Vagus Nerve is in regulating the parasympathetic response.

Some of the major actions of the Vagus Nerve in various organs include:

  • Decreasing heart rate and blood pressure

  • Slowing breathing rate and constricting bronchi

  • Regulating insulin and enzyme secretion from the pancreas

  • Stimulating bile release from the liver

  • Increasing stomach acid secretions

  • Increasing gut motility through peristalsis

  • Motor function in the throat including swallowing, coughing, and gagging

  • Increasing cholinergic neuron activity

---- When the vagus nerve is underactive, we can have issues with any number of these systems.

In a chronically stressed state, we are under the influence of the Sympathetic “Fight-or-Flight” state— which works in opposition to the Parasympathetic “Rest-and-Digest” system. Essentially, stress (the ‘gas’) takes over and the parasympathetic nerves (the ‘brakes’) are powerless.

Vagus Nerve 101 Foundation of Functional Medicine

The Impacts of Poor Vagal Tone

Without the activation from the Vagus Nerve, we have poor breakdown of food (less enzymes/acid/bile), impaired digestion (less blood flow and activity in the small intestine), blood sugar dysregulation (lack of proper insulin response), and decreased immune surveillance (poor oral tolerance).

Ultimately, this manifests as constipation/diarrhea, gas/bloating, nutrient deficiencies, mood changes, depression/anxiety, inflammation; and can lead to further issues like SIBO, Leaky Gut, Chronic Inflammation, Autoimmune Disease, Diabetes, and Neurological Dysfunction.

We think of the Vagus Nerve often in the context of the gut-brain axis. The Vagus Nerve is the key connection here- sending signals in both directions. When we have gut problems, it’s likely they show up as brain problems (and vice versa).

The Vagus Nerve & The Immune System (The Neuro-Immune Axis)

However, it is not to be ignored that the Vagus Nerve is also an important bridge between the nervous system and the immune system. This is another bi-directional connection. When the Vagus Nerve is functioning poorly, immune modulators in the spleen are influenced into production of inflammatory cytokines and antibodies.

Now, you have increased inflammation in the body, which eventually shows up as brain inflammation. This means less “Frequency of Firing” in the cortex. With less FOF, you have less vagal nerve activation from the brain… thus further reinforcing a loop of dysfunction. We can find ourselves in these same webs of issues as it relates to gastrointestinal/immune/cognitive function regulated by the Vagus Nerve.

>> Calming down the stress response and taming an overactive immune system is essential in restoring Vagal Nerve tone. <<


How To Improve Vagus Nerve Activation:

The positive here is that we can find ways to influence the activity of the Vagus Nerve from a “Top-Down” and a “Bottom-Up” approach.

TOP-DOWN APPROACHES: We can use things like meditation, deep breathing, and cognitive behavioral therapy to shift the nervous system away from a sympathetic state. Hormetic stressors like cold exposure, infrared sauna, and fasting can help retrain the stress response to an adequate balance.

Alternatively, we can improve Vagal Nerve tone with motor activation through chewing, humming, gargling, and gagging. Transcutaneous Vagal Nerve Stimulation (TVNS) is a safe, non-food, non-chemical way to directly activate the Vagus Nerve using electrical stimulation.

BOTTOM-UP APPROACHES: From the bottom, we consider an elimination diet to lower intestinal inflammation, probiotics for microbiome balance, and a low-glycemic approach to meals and snacks for blood sugar control. We can also encourage regular motility with abdominal massage, proper hydration, and adequate fiber.


Elimination Diet PDF Guide by Functional medicine doctor and functional nutritionist


...We're not done on this topic, stay tuned for more from the Functional Medicine Team at The Facility.

Mitchell Rasmussen Functional Medicine Doctor Denver Colorado

Dr. Mitchell Rasmussen, DC, CFMP serves as Director of Functional Medicine at The Facility in Denver, CO. He sees patients in-person and via Telehealth to get to the root cause of dysfunction and restore a state of well-being using nutritional intervention, supplementation, and lifestyle change.


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An Introduction to the Vagus Nerve - Functional Medicine - The Facility Denver


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