Dr. Stephanie Canestraro, The Vagus Clinic
The vagus nerve may also be referred to as the tenth cranial nerve or simply "cranial nerve ten." As implied by its name, this large cranial nerve originates at the base of your brain (inferior to your cerebellum), descends down through your neck, chest, stomach (inferior border of your diaphragm), and finally ends in your pelvic region. The vagus nerve is partly responsible for the parasympathetic response (Rest and digest) that influences vagal tone, which in turn is heavily involved with autonomic nervous system function.
The vagus nerve plays a role in immune health, cognitive function, mood, sleep quality, satiety/hunger levels, stress management, athletic performance, clear communication between the gut and brain, intestinal motility (the rate at which food moves through the digestive tract), visceral sensitivity (the physical awareness of body sensations), taste perception, mucosal secretion (lining your respiratory passages) and more.
The vagus nerve is the key to vagal tone, which can be thought of as vagus nerve strength. Since vagal tone has been shown to improve clinical symptoms, metabolic function, and autonomic nervous system balance, it's of great interest for those who are looking to optimize their health.
Since vagal tone influences the parasympathetic nervous system (the "rest and digest" response of your body), vagal tone is thought to be a prime regulator of the body's stress-recovery balance.
The vagus nerve can improve athletic performance by increasing vagal tone, which in turn slows down heart rate, lowers blood pressure, reduces levels of cortisol, boosts immune function, increases tissue perfusion by vasodilation, prevents muscle catabolism/fatty acid breakdown during exercise, improves oxygen delivery to muscles, and suppresses gut motility.
Vagus nerve stimulation has been shown to increase exertion threshold so that an appropriate level of force was not wasted on unnecessary physical activity. This suggests vagus nerve stimulation can increase oxygen delivery to muscles and allow the body to work at a higher intensity but without increasing fatigue. In vagal tone, one's response changes from being inhibitory to sympathetic or from stimulation to excitation.
Vagus nerve stimulation has been shown in athletes as a way of promoting improved performance through vagal inhibition. Researchers have found that vagus nerve stimulation increases parasympathetic effects, increases heart rate variability, and decreases cortisol levels. Vagus nerve stimulation also helps develop muscle mass by increasing testosterone release.
In those with chronic illness including post-traumatic stress disorder, vagus nerve stimulation is used as part of vagal interventions for treatment of depression, anxiety disorders, cardiac conditions such as high blood pressure and congestive heart failure, and disorders of the digestive system.
Vagus nerve stimulation has been successful in vagal interventions used to treat conditions such as attention-deficit hyperactivity disorder, drug-resistant epilepsy, and autism spectrum disorders. Researchers have also investigated vagal nerve stimulation as a way to help those with inflammatory bowel disease.
Physical stressors such as increased inflammation or increased intestinal permeability have been shown to lead to vagal dysfunction. Inhibition of one's vagus nerve inhibits the body's ability to fight autoimmune disorders, as well as inhibiting insulin levels, glucose tolerance, fat metabolism, and the release of pro-inflammatory cytokines.
Heart rate variability is considered the gold standard for assessing vagal tone. Heart rate variability refers to the beat-to-beat fluctuations in intervals between heart beats and can be expressed as a percentage or on a scale from zero to 100. A healthy vagal tone will show high HRV (80-100%) whereas vagal inhibition (low vagal tone) is associated with low HRV.
A study showed vagus stimulation (VNS) can offer therapeutic benefits for patients suffering from irritable bowel syndrome by modulating intestinal inflammation. Vagus nerve stimulation using an implantable device remains under investigation for use in the treatment of inflammatory bowel disease, but there are much easier ways from home that you can start to tone your vagus nerve.
Respiratory sinus arrhythmia (RSA) refers to the change in heart rate on inhalation and exhalation. This test functions like an active vagal tone test, as vagal tone increases on exhalation, causing RSA to rise; conversely, vagal tone decreases on inhalation causing RSA to fall. Therefore taking repeated readings over time of your heart rate variability and respiratory sinus arrhythmia can give you a picture of how vagal function changes daily under arousal or stress conditions.
You can also measure Salivary Flow Rate. A healthy vagal tone response will cause increased salivation production that peaks 2-3 minutes after a meal, which washes food through the digestive tract and signals the body to stop eating.
Low vagal tone may be treated with probiotics, specific vagal toning exercises, lifestyle choices, and other supplements, but in cases where chronic illness is present, it would be best to work with a functional medicine practitioner who has experience treating the vagus nerve in chronically ill individuals.
The vagus nerve has been shown to regulate inflammation in the gut, chronic illness, vagal interventions for mental health conditions, vagal tone levels, athletic performance, and more. Vagus nerve stimulation through vagal interventions has many applications for chronic illness. If vagus function is too low it can be increased by deep belly breathing, which increases vagal tone. Deep belly breathing can be optimized using an app like Paced Breathing or one that measures Heart Rate Variability to maximize vagus nerve function.
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