The vagus nerve is the longest cranial nerve, emerging from the bottom of the brain to influence primary "automatic" bodily functions, such as breathing, heartbeats, and the various functions of the gastrointestinal tract. While the presence of the nerve has been known for decades, it's only a recent discovery that most of the information flows from the gut to the brain rather than from the brain to the gut. This information highway gives the brain a lot of data from the intestines (also known as the gut).
Because of its nerve connections throughout the body, this information super highway can either increase or decrease the activity of significant systems in the body: respiratory, circulatory, and digestive. The Autonomic Nervous System (ANS), which regulates the automatic functions in the body such as breath and heart rates, uses the vagus nerve to excite or depress multiple organs simultaneously, depending on the need to "rest and digest" or engage in "fight or flight." What happens if this crucial nerve sustains damage? Since this nerve has access to so many bodily functions, what symptoms signal an issue?
To Excite or Depress: The Role of the Vagus Nerve in the Autonomic Nervous System
The vagus nerve is a bundle of nerve fibers connecting the brain to the lungs, heart, stomach, intestines, and other organs. Not only is this a physical connection between the brain and organs, but it executes complex communication based on the reactions to the environment by the ANS. Recall that the ANS is composed of two competing forces, the parasympathetic and sympathetic processes. These processes are designed for one to be most predominant at a time in response to the environment.
Parasympathetic processes of the ANS - These are the "rest and digest" default settings of the human body. This relaxed mode with a normal heart and breath rate allows digestion to occur, as well as recovery from exertion. The vagus nerve is home to roughly 75% of the body's parasympathetic nerve fibers involved in digestion and physical recovery (1).
Sympathetic processes of the ANS - This "fight or flight" emergency mode prepares the human body to defend itself or flee. During these moments, blood is directed towards muscles used to run or fight, the eyes dilate to take in as much information as possible, and the heart rate is increased dramatically. Parasympathetic processes are suppressed.
In broad terms, the vagus nerve assists in three essential functions: converting emotions to actions, returning the system to default settings after an emergency, and fine-tuning functionality. Let's look at each of these in-depth:
1. Converting Emotion to Action - While the vagus nerve affects many bodily functions, it also responds to many emotions. It is the perception of danger that kicks off the "fight or flight" response of the ANS. The threat does not have to be real. You only have to believe that you may be in danger to cause a dramatic increase in heart and breath rate. Merely fearing something or being anxious about something can have the same result as an imminent physical threat. Based on the emotion being strongly experienced, the ANS uses the vagus nerve to communicate the necessary actions to the appropriate organs.
2. Returning the System to Normal - The sympathetic part of the ANS (the "fight or flight" mode) should only exist as long as the danger exists. It's an emergency response, not the normal state of being. One of the most critical functions of the ANS is to return the system to a normal state of rest once the danger passes. As the threat of danger subsides, the sympathetic functions should fade away too, and the parasympathetic mode should take over.
3. Fine Tuning Day-to-Day Restful Functions - The vagus nerve is involved in many crucial functions as a significant connection between the brain and organs. Keep in mind the ANS can manipulate these vagus nerve functions dramatically or in tiny increments to adjust to the environment (1, 2):
Changes breath and heart rates
Increases or decreases rate of digestion and immune system response
Manipulates levels of saliva and mucus creation
Increases or decreases arterial pressure (aka "blood pressure")
Affects vocal cord activation
Impact of Chronic Stress on the Vagus Nerve
As stated previously, the vagus nerve assists the ANS when it attempts to return the body to the "rest and digest" mode after an emergency has passed. Unfortunately, some people have so much stress in their lives that their body is constantly in an emergency, "fight or flight." Stress responses can repeatedly stimulate the sympathetic nervous system, causing someone to stay in an almost perpetual state of emergency. Being constantly under stress in this manner makes it harder for the ANS to return the body to its normal, non-emergency functions. Luckily, research has shown that applying electrical stimulation to the vagus nerve increases parasympathetic "rest and digest" functions, which begins to decrease sympathetic roles. Vagus nerve stimulation (VNS) helps treat severe conditions of chronic stress, such as post-traumatic stress disorder (PTSD) (1).
What Are Some Common Vagus Nerve Disorders? Who is at Risk?
One can see that the ANS is meant to balance "rest and digest" with "fight or flight." The body needs both functions at different times, and staying stuck in one or the other state would cause issues. It is also apparent this complex system, exquisitely responsive to emotion, is subject to more potential problems than a simple system. Dysfunction of the vagus nerve could result from physical damage to the nerve fibers, or the nerve fibers can become dysfunctional in their responses.
Gastroparesis and vasovagal syncope are two common vagus nerve conditions (1).
Gastroparesis - This condition of "stomach paralysis" occurs when food does not get adequately moved from the stomach to the intestines due to damage of the vagus nerve (3). It's a somewhat rare condition, but rising rates of diabetes may make it more common. Vagus nerve damage, in this case, is typically caused by diabetes or surgery (3):
Diabetes - Consistently high blood sugar levels can physically damage nerves, including the nerves that signal the stomach to empty its contents into the small intestine. Since those with diabetes have sustained high blood sugar levels, it increases their risk of developing gastroparesis.
Surgery - Certain surgeries on parts of the abdomen or digestive tract can inadvertently damage or remove portions of the vagus nerve, such as gallbladder removal, removal of parts of the pancreas, and gastric bypass surgery. A history of these types of surgeries increases the risk for gastroparesis. (Note, sometimes the vagus nerve connections are intentionally cut due to over-activation, for example, to treat peptic ulcer disease) (4).
Vasovagal Syncope (VS) - A sudden drop in heart rate and blood pressure (usually resulting in fainting) characterizes an episode of VS. As a reflex action, it can't be consciously controlled (5). One-third of the population will have an episode of VS in their lifetimes, though, for people under the age of 40, it is responsible for almost 85% of all fainting spells (5).
VS can be thought of as a poor "handoff" between the sympathetic and parasympathetic processes of the ANS, causing blood pressure and heart rate to suddenly drop, which deprives the brain of oxygen and results in fainting. An episode is quick, typically lasting under a minute from fainting to recovery. While the underlying causes are still being explored by researchers, here are a few facts about triggers and possible causes of VS:
Emotional triggers - VS can be triggered by "extreme emotional distress” (6), including the sight of blood or a frightening event.
Physical triggers - Hunger, anxiety, and pain can trigger VS (1). During bowel movements, strain can cause a VS episode (6). Heat is enough to trigger some sufferers (6).
Dysfunctional reflex - The reflex underlying VS is normal, but in the case of VS, the reflex is either too strong or happens at the wrong time (5). This dynamic is not completely understood.
Because the vagus nerve touches so many organs, connecting the dots to symptoms can be challenging. It takes an experienced doctor to eliminate other causes of these symptoms. Here are just a few of the possible signs of vagus nerve disorders or conditions (1):
Digestion-related: acid reflux, pain and bloating in the abdomen, problems swallowing or lack of a gag reflex, nausea, vomiting, low appetite, feeling abnormally full with a small amount of food intake
Cardiovascular-related: feeling dizzy, fainting, blood pressure or heart rate changes
Vocal cord-related: hoarseness, weakening, or loss of the voice
Complications from Lack of Treatment
For some, the worst negative repercussion of not treating a vagus nerve disorder is falling down. It's difficult to break a fall if you faint suddenly. For those experiencing gastroparesis, lack of treatment could cause a worsening of gastrointestinal issues, including weight loss and the inability to absorb nutrients adequately. Nutritional deficiencies can sap strength, vitality, and mental sharpness, triggering more serious issues as the deficiency deepens. When vocal cord innervation is involved, not treating the vagus nerve could result in difficulty speaking. Lastly, allowing stress to become chronic can cause your sympathetic nervous system to become constantly overstimulated, making it harder for your body to relax, recover, and digest properly.
Prevention - In many ways, preventing vagus nerve issues resembles basic self-care that includes:
Proper screening - Many tests and blood screenings can help diagnose a vagus nerve issue, such as testing blood pressure, heart rate, or the stress hormone cortisol. However, one type of screening stands out for vagus nerve issues - plethysmography testing. The details of how we use fingertip plethysmography testing are in our article on endothelial dysfunction. This non-invasive screening using a simple finger clamp estimates ANS activity, quickly identifying signs that the body is stuck in "fight or flight" sympathetic mode. Plethysmography testing can be performed as a part of our Executive Physicals if the doctor suspects this issue.
Control high blood sugar (1) - One of the best things you can do to prevent issues with the vagus nerve is to control high blood sugar. Consistently high blood sugar damages nerve endings and can damage vagus nerve fibers.
Control blood pressure issues (1) - Low blood pressure can lead to vasovagal syncope issues, but high or low blood pressure, if not controlled, can negatively affect the vagus nerve.
Manage stress - Do not underestimate the ability of stress to disrupt a system! Exercise, play, and get good sleep to counter the effects of stress. Anything you can do to reduce stress will help the health of your nervous system and your whole body.
Practice stress-reducing techniques (1) - Exercises that lower the heart rate, involve conscious breathing, or help focus the mind can help the ANS return the system to "rest and digest." Meditation, qi gong, yoga, and breathwork can directly or indirectly benefit the health of the vagus nerve. There are many excellent online resources, but practicing in person (joining a nearby community of practitioners) can give an added boost to your well-being by fostering social ties.
Gargle or hum - Because the structures of the throat, vocal cords, lungs, and diaphragm are intricately connected with the vagus nerve, gargling or humming can give the vagus nerves a little workout.
Treatment suggestions will vary depending on the nature of the vagal nerve issue. All of the prevention tips above can be used as treatments, depending on the nature and severity of the symptoms. Consulting with a doctor will ensure you get the best treatment for your needs. Other treatments might include:
Medications - Treating conditions affecting the vagus nerve may mean taking medication for diabetes, blood pressure issues, or other conditions.
Acupuncture - Some research indicates that stimulation of specific acupuncture points can activate the parasympathetic ANS functions (7). Indeed, acupuncture can help the body reduce stress, alleviate pain, and reduce symptoms of fear and anxiety that could trigger sympathetic ANS functions.
Vagus Nerve Stimulation (VNS) - Applying painless electrical stimulation directly to the vagus nerve through a small device implanted under the skin sends signals to the brain, calming brain activity (1).
Remedies for many vagus nerve issues are simple and non-invasive.
Finger plethysmography testing helps TCIM doctors evaluate the health of the autonomic nervous system, positively identifying overstimulation of the "fight or flight" sympathetic response. If you have some of the symptoms listed above, partner with TCIM by scheduling an Executive Physical for a full workup. We have superb diagnostic, nutrition, and acupuncture services to help preserve and treat vagus nerve function.
Jonathan Vellinga, MD is an Internal Medicine practitioner with a broad interest in medicine. He graduated Summa cum laude from Weber State University in Clinical Laboratory Sciences and completed his medical degree from the Medical College of Wisconsin.
Upon graduation from medical school, he completed his Internal Medicine residency at the University of Michigan. Dr. Vellinga is board-certified with the American Board of Internal Medicine and a member of the Institute for Functional Medicine.
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