What is the Vagus Nerve?
Roles and Functions
In people with fatigue, food sensitivities, anxiety, gut problems, brain fog, and depersonalization, vagal nerve dysfunction is almost always at play. These people have lower vagal tone, which means the nerve has a lower ability to perform its functions.
The only question is which aspect of the vagus nerve is malfunctioning and to what extent it is the problem vs. other aspects of your biology.
The vagus nerve is part of the parasympathetic nervous system, referred to as the rest-and-digest system. It’s not the only nerve in the parasympathetic system, but it’s by far the most important one because it has the most far-reaching effects.
The word vagus means “wanderer,” because it wanders all over the body to various important organs.
The vagus nerve affects the brain, gut (intestines, stomach), heart, liver, pancreas, gallbladder, kidney, ureter, spleen, lungs, reproductive organs (female), neck (pharynx, larynx, and esophagus), ears, and tongue.
Given the importance of the vagus nerve to the gut, when it’s not working properly, it will cause digestive disorders including dyspepsia, gastroparesis, GERD, ulcerative colitis, anorexia, and bulimia, to name a few.
Your vagus nerve system can be messed up in 3 main ways:
- Communication from an organ to the brain.
- Communication within the brain.
- Communication from the brain to other areas of the body like the heart, liver, and gut.
How It Affects Your Body
In the brain, the vagus nerve helps mood and controls anxiety and depression.
The vagus nerve is largely responsible for the mind-body connection since it goes to all the major organs (except the adrenal and thyroid glands).
It’s intimately tied to how we connect with one another – it links directly to nerves that tune our ears to human speech, coordinate eye contact, and regulate emotional expressions. It influences the release of oxytocin, a hormone that is important in social bonding .
Studies have found that higher vagal tone is associated with greater closeness to others and more altruistic behavior .
Vagus activity of a child can be affected by their mother. Infants had lower vagus activity with mothers who were depressed, angry, or anxious during pregnancy .
Some studies suggested that the vagus nerve is important for getting in the mental state of “flow”. It’s believed that the combination of sympathetic (fight-or-flight) and vagus activation creates the right environment for a flow state .
Vagus nerve stimulation might increase wakefulness (by increasing orexin in the prefrontal cortex). It has been shown to decrease the amount of daytime sleep and rapid eye movement in epilepsy patients with traumatic brain injury and also promoted the recovery of consciousness in comatose rats after traumatic brain injury .
However, overactivating the vagus nerve also might cause ‘sickness behavior’ (fatigue, sleepiness, depression, anxiety, appetite loss, pain, lowered motivation, and failure to concentrate) when activated by inflammatory markers in an inflammatory state (IL-1b) .
In the gut, it increases stomach acidity, digestive juice secretion, and gut flow. Since the vagus nerve is important for increasing gut flow (motility), having less vagus activation will increase your IBS risk, which is a result of slower flow .
Stimulating the vagus nerve increases the release of histamine by stomach cells, which helps release stomach acid . So, low stomach acidity is usually, in part, a vagus nerve problem. By releasing the intrinsic factor, the vagus nerve is important to help you absorb vitamin B12.
Satiety and relaxation following a meal are in part caused by activation of the vagus nerve’s transmission to the brain in response to food intake .
The vagus nerve is important in conditions like GERD, not only because it controls stomach acidity, but also because it controls the esophagus.
Liver, Pancreas, and Gallbladder
In the liver and pancreas, it helps control blood glucose balance.
In the gallbladder, it helps release bile, which can help you get rid of toxins and break down fat.
In the heart, it controls heart rate and blood pressure. A very promising study on heart failure showed improvements with vagal nerve stimulation .
Kidney and Bladder
The vagus nerve promotes general kidney function. It helps with glucose control and increases blood flow, which improves blood filtration. Vagus activation also releases dopamine in the kidneys, which helps excrete sodium and, thereby, lower blood pressure [10, 11].
The vagus nerve also goes to the bladder. A side effect of its stimulation is urinary retention, which means that less vagus stimulation can cause you to urinate frequently. Indeed, many of my clients complain about frequent urination (also due to low vasopressin, low aldosterone, and high cortisol) [12, 13].
In the spleen, it can reduce inflammation. Note that vagus activation will reduce inflammation in all target organs (by releasing acetylcholine), but when it activates in the spleen the response will probably be more systemic .
It helps control fertility and orgasms in women by connecting to the cervix, uterus, and vagina. Women can actually experience orgasms simply from the vagus nerve.
Mouth and Ears
In the tongue, it helps control taste and saliva; while in the eyes, it helps release tears.
The vagus nerve explains why a person may cough when tickled on the ear, such as when trying to remove ear wax with a cotton swab.
Vagus nerve stimulation helps people with tinnitus because of its connection to the ear.
Potential Symptoms of Low Vagal Tone
- Obesity and weight gain 
- Brain problems
- Chronic fatigue
- High or low heart rate
- Difficulty swallowing
- Gastroparesis, also known as delayed gastric emptying
- B12 deficiency
- Chronic inflammation
Conditions That May Improve From Vagus Activation
Since the vagus nerve is associated with many different functions and brain regions, research shows the positive effects of vagal stimulation on a variety of conditions, including but not limited to:
- Anxiety Disorders
- Heart disease
- Alcohol addiction
- Multiple sclerosis
- Chronic heart failure
- Memory disorders
- Mood disorders
- Cancer 
- Bad blood circulation 
- Leaky Gut
- Severe mental diseases
Additional Vagus Nerve Resources
You can stimulate or inhibit the vagus nerve in two ways. First, the vagus nerve impulse (activation) can flow from the brain to the rest of the body or from the body to the brain.
When it flows from the brain it’s called a “vagal efferent.” When it flows from other parts of the body to the brain, it’s called a “vagal afferent.” I don’t use these terms for simplicity.
The low-frequency HRV is associated with both sympathetic (fight or flight) and parasympathetic (rest and digest) activation.
Genetic Testing for Vagus Activity and the Benefit of Knowing your Genomics
This gene test is a great example of how empowering it is to know your genomics. Based on your genetic propensity, you may easily stimulate the vagus nerve or may be more to have low vagal tone. It’s so easy to do daily healing rituals to stimulate your own vagus nerve and thereby help all types of body functions.
You can upload your genetic data to SelfDecode, a sister company of SelfHacked, and see if you have the version of the gene associated with low activity.