The Vagus Nerve, Explained

Good morning!

Hopefully your spring looks like open windows, long walks, and actual fresh air. Not being stuck inside because your body decided pollen is public enemy number one. If you’re dealing with itchy eyes, congestion, or that constant foggy feeling, just know you’re not alone. And yes, there will probably (definitely) be a deeper dive on that next week.

But this week, we’re getting into something that’s not really all that known. Ever wonder how your heart keeps beating, your lungs keep breathing, and your digestion keeps moving all without you thinking about any of it? The answer to all these is the vagus nerve. Let’s dig in.

Key Takeaways

• The vagus nerve runs from the brainstem to major organs and is mostly sensory, sending about 80% of signals from body to brain.

• It helps slow heart rate, regulate digestion, more by sensing what’s happening in the body.

• Its baseline activity (“vagal tone”) reflects how well you regulate stress and inflammation. Stimulating it is even used clinically for conditions like epilepsy, depression, and inflammatory disease.

CORE

What the Vagus Nerve Is

The vagus nerve is actually two nerves, a left and right branch, that exit from your brainstem and travel down either side of your body. "Vagus" is Latin for wandering, which perfectly describes its path as it wanders through your neck, chest, and abdomen, branching off to connect with your heart, lungs, digestive tract, liver, spleen, and kidneys.

It's called a "mixed nerve" because it carries signals in both directions. About 80% of its fibers are afferent, meaning they carry sensory information from your organs up to your brain. The remaining 20% are efferent, carrying motor commands from your brain down to your organs.

This matters because the vagus nerve isn't just your brain controlling your body. It's mostly your body reporting to your brain what's happening.

Your Resting Heart Rate

Your heart has its own pacemaker, the sinoatrial (SA) node, that generates electrical impulses causing your heart to beat. Without any external input, this node fires at about 100-110 beats per minute.

Obviously, you're not walking around with a resting heart rate of 100. The reason is because your vagus nerve is constantly active, applying what's called "vagal tone”. The vagus nerve releases the neurotransmitter acetylcholine onto cells in the SA node. Acetylcholine binds to receptors on these cells and triggers a cascade of chemical reactions that slow the pacemaker activity down. This brings your resting heart rate down to 60-80 beats per minute.

Now, what exactly is the vagal tone I mentioned? It refers to the baseline level of activity in the vagus nerve, or how much continuous parasympathetic influence it's exerting on your body at rest.

Higher vagal tone is generally associated with better regulation: more stable heart rate variability (the healthy variation in time between heartbeats), better stress resilience, more effective digestion, and better control of inflammation. Lower vagal tone is associated with poorer regulation across all these systems.

Importantly, vagal tone isn’t fixed. It tends to improve with regular aerobic movement, quality sleep, slow breathing practices, and strong recovery from stress. On the other hand, chronic stress, poor sleep, inactivity, and excess alcohol can all dampen its function over time, shifting the system toward a more “stuck on alert” baseline.

Digestion

After you eat, your body has to do more than just “sit and process” food. It needs to break it down, absorb nutrients, and move everything along the digestive tract in a coordinated way. The vagus nerve plays a central role in helping this system run smoothly.

When food enters the stomach, stretch receptors in the stomach wall detect the expansion and send signals up through the vagus nerve to the brainstem. The brain then responds by sending signals back down through the vagus nerve to the digestive organs. These signals help increase muscle contractions that move food forward through the gut and stimulate the release of digestive enzymes and stomach acid, both essential for proper breakdown and absorption.

This is also where stress becomes relevant. When the body shifts into a sympathetic “alert” state, vagal activity is reduced. In that state, the body prioritizes immediate action over digestion, which can lead to slower gut movement and reduced digestive secretions. In other words, less vagal influence means less coordination of the processes that keep digestion moving efficiently.

Medical Applications

The vagus nerve is not only something the body uses naturally, it is also something medicine can actively support. In recent years, clinicians have learned that stimulating this nerve can shift how the brain, body, and immune system regulate themselves.

This is done through vagus nerve stimulation (VNS), where small implanted devices send gentle electrical impulses to the nerve. Those signals travel upward to the brain and influence broad regulatory systems involved in neural activity, mood, and inflammation. VNS is an FDA-approved therapy for conditions such as epilepsy and treatment-resistant depression, and it is also being studied for inflammatory diseases.

The key idea is not the specific diagnoses, but what this demonstrates. That by modulating the vagus nerve, it is possible to influence how the brain regulates activity and how the body manages physiological and inflammatory responses. In other words, this is one of the clearest real-world examples of the vagus nerve acting as a bridge between internal organ function and central nervous system control.

ENDNOTE

Final Thoughts

An important note, the vagus nerve is not solely responsible for these involuntary functions, though it does play a crucial role in each. And as you can imagine, this fascinating nerve is involved in countless other functions not included in this newsletter.

Got an extra 5 minutes? Check out this edition, where I break down the very relevant magnesium-heart health link.

Until next week!

Adrian Macdonald | Team Dietitian | The 8% Newsletter Author