Vagal Tone: The Gut-Brain Axis & the Vagus Nerve

Have you ever had a “gut feeling” about something, or felt “butterflies” in your stomach? That gut feeling is actually your vagal tone, the communication signal from your gut to your brain. The higher the vagal tone is, the faster your body can relax after feeling stress. Don’t worry, I’m going to tell you ways to increase your vagal tone in just a bit. 

Your body is an intelligent, interconnected system that works hard to keep you safe and healthy. The vagal tone, what you might think of as your “gut instinct,” is why your digestive system is so in tune to your emotions.

The profound connection between your brain and gut, known as the gut-brain axis, is controlled by millions of neurons that run throughout your nervous system, sending signals from the brain to the gut, and vice versa.¹

When your mouth waters at the thought of your favorite meal, or your stomach feels queasy in the days leading up to a big meeting, those are signals bouncing around your nervous system as your gut and brain communicate with one another. Most of these signals are transmitted through a long cranial nerve called the vagus nerve. 

I’m going to tell you all about the gut-brain axis, how it affects your health, how you can test your vagus nerve function, and how you can stimulate your vagus nerve. First, let me tell you about the vagus nerve. 

What is the Vagus Nerve?

There are two parts to your nervous system: The central nervous system (CNS) and the peripheral nervous system. Your brain and spinal cord make up the CNS while your peripheral nervous system is made up of many nerves that branch out from the CNS. 

The peripheral nervous system is further divided into two parts – the somatic nervous system, which guides your voluntary movements such as playing the piano or dancing, and the autonomic nervous system, which guides your involuntary movements such as breathing, heart beating and digesting your food. That may seem a bit complicated, yet for this discussion it’s important to know that the vagus nerve is part of the autonomic nervous system. 

The vagus nerve plays an important role in digestion, regulating your heart rate and blood pressure, facilitating immune system responses, your mood, speech, what you taste, and how much you pee.²

Monitoring your vagal tone, or the impulses from your vagus nerve will help you understand how well your vagus nerve is functioning. I’ll tell you how to monitor your vagal tone later. Let’s talk more about what the vagus nerve does. 

What is the Function of the Vagus Nerve?

As I mentioned, the vagus nerve controls your involuntary functions such as breathing and digestion. The vagus nerve is the main line of communication between your brain and your gut, also known as the gut-brain axis. It sends signals, the vagal tone, in both directions.³ These signals tell your body to perform these involuntary actions that you may not even know is happening. Let’s take a look at the actions that are regulated by your vagus nerve.

Digestion

When you digest food, the vagus nerve recognizes changes in your gut’s microbiome and sends this message to the brain. When it works properly, the brain replies with the correct digestive response immediately. For example, if you eat an inflammatory food such as gluten or dairy, the vagus nerve recognizes this inflammation and alerts your brain. Your brain then alerts your immune system to facilitate an inflammatory response. Very similar to calling the fire department to put out a fire. 

If your vagus nerve isn’t working properly, then the signal is weaker and the brain might miss important information. Imagine being on your cell phone with a weak signal and the conversation is choppy and you miss parts. If the vagus nerve can’t communicate the inflammation properly because of a weak signal, the inflammation can continue to grow and become chronic. Chronic inflammation is the leading cause of autoimmune disease. 

Heart Rate and Blood Pressure

Just as it sends signals to your brain about your gut, the vagus nerve also sends signals to the brain to control your heart rate and blood pressure. It’s not the reason your heart beats, but it is the reason your heart rate slows down. Let me explain. If you are under stress, your brain signals your adrenal glands to release cortisol. Cortisol mobilizes glucose reserves for energy and facilitates the consolidation of fear-based memories so you can survive in the future and avoid danger. Too much cortisol can increase your heart rate and blood pressure. 

When the vagus nerve recognizes this increase, it sends a vagal tone to the brain to “cool it.” The brain responds by releasing serotonin, which helps lower the heart rate and blood pressure. 

Sometimes the vagus nerve can become overstimulated and overreact. There’s no clear cause as to why, however, some studies have shown that stress, a hormone imbalance, and inflammation can trigger an overreaction by the vagus nerve. This is called vasovagal syncope, which is a sudden drop in your heart rate or blood pressure. The most visible sign of this is fainting, however, you may also experience excessive sweating, fatigue, blurred vision, or ringing in your ears.⁴

Mood

Two of the more important functions of the vagus nerve are your heart rate and digestion, yet it also plays a role in your mood. This makes sense if you consider the vagus nerve’s primary function is to send signals to and from the brain and your gut. 

The vagus nerve is what counterbalances the fight or flight response when you are faced with a stressful situation. As I mentioned, when you’re faced with stress your brain signals your adrenal glands to release cortisol. When cortisol levels get too high, the vagus nerve signals the brain to release serotonin to balance this stress response. The vagus nerve also signals the brain to release other feel good hormones such as oxytocin, endorphins, and dopamine. 

Regulating your mood, heart rate, blood pressure, and digestion are the primary jobs of the vagus nerve. However, it also helps control saliva production, muscle movement, urine output, and your speech. Yet, sometimes it doesn’t work the way it should. Let’s talk about what can go wrong with the vagus nerve. 

What Can Go Wrong with the Vagus Nerve?

When working optimally, the vagus nerve is able to send vagal tones all over the body. What happens when it doesn’t work the way it’s supposed to?  

When your body is exposed to long periods of infection, inflammation, and chronic stress, the vagus nerve becomes overworked and begin to lose signal. Remember the cell phone analogy? Early warning signs that something has gone array with your vagus nerve include:

• Brain fog
• Fatigue
• Muscle aches
• Chronic headaches

Over time, a dysfunctional vagus nerve can lead to:

• Abdominal pain and bloating
• Acid reflux
• Changes to heart rate, blood pressure, or blood glucose levels
• Difficulty swallowing or loss of gag reflex
• Dizziness or fainting
• Hoarseness or loss of voice
• Unexpected weight loss
• Loss of appetite
• Nausea of vomiting

The good news is that your functional medicine doctor can order tests to determine if vagal nerve dysfunction is the root cause of your symptoms. 

Testing the Vagus Nerve

There are tests your doctor can do to detect a problem with your vagus nerve, such as an MRI, CT scan, or an echocardiogram. Other methods include a gag-reflex test, a look at your heart health history, and a stress test to measure your heart rate when you exercise. Here’s how they work: 

Gag-Reflex Test

To do a vagus nerve gag reflex test, your doctor will use a soft cotton swab and gently touch it to the back of your throat. They will touch the cotton swab to both sides to stimulate both vagal nerves. In a person with a healthy vagus nerve, this sensation should cause them to gag. If a person does not gag during this test, it could indicate that there is an issue with their vagus nerve.

Cardiovascular Disease History

Since the parasympathetic nervous system controls your heart rate, your doctor will want to review your history of cardiovascular health. Evidence points to a strong correlation between heart failure and parasympathetic activation, which shows that vagal nerve dysfunction can be linked to ventricular dysfunction.⁵

Stress Test

The vagus nerve sends a vagal tone to the lower right chamber of your heart to increase the heart rate to the need for more blood flow during exercise. When you stop exercising, your vagus nerve sends a signal to the brain to reduce the heart.⁶ If your heart doesn’t slow down within 10 minutes of the end of the exercise, that could indicate a problem with the vagus nerve. 

Now that you know about the vagus nerve, what it does, and what can go wrong, you might be wondering how you can stimulate the vagus nerve. I’m about to tell you the ways you can stimulate your vagus nerve to function optimally. 

How to Increase Your Vagal Tone

Your vagus nerve can lose its ability to send vagal tone signals as you get older. This is known to increase your risk for heart disease, high blood pressure, type 2 diabetes, and depression. 

Vagus nerve stimulation (VNS) is used to treat seizures in people with epilepsy and stimulate the vagus nerve responses. It’s also used to help people with depression. However, this requires an invasive medical procedure to place a VHS device in your body. 

If that isn’t practical for you, there are other ways to naturally stimulate the vagus nerve, including yoga and meditation, even gargling can stimulate the vagus nerve. Here are some simple methods of vagus nerve stimulation: 

• Deep breathing exercises & meditation
• Doing yoga
• Cryotherapy or taking an ice bath
• Singing and dancing
• Gargling water
• Eat a healthy diet of organic lean protein and fruits, and vegetables. 

Your vagus nerve affects your physical and mental health in many ways, so it’s important to take care of it with the above exercises. I also recommend adding additional support through supplementation.  

Additional Support for Your Vagus Nerve 

The vagus nerve controls your heart, stress response, and gut health, so providing your body with additional support is essential for optimal health. 

ZenAdapt™ is an adaptogenic herbal blend for fast-acting, profound relaxation. Your vagus nerve signals your stress response and tells your brain that it’s time to calm down when the threat is no longer there. Adding ZenAdapt™ supports a balanced stress response and contains botanicals and micronutrients for supporting healthy cortisol levels.

The vagus nerve is the largest nerve in your body that is responsible for so much of your involuntary functions. If you’re having digestive issues, brain fog, irregular heartbeats, or notice that you’ve lost your gag reflex, your vagus nerve could be sending weak vagal tone signals to and from your brain and gut. Using these tools can stimulate your vagus nerve to get it working optimally.