Gut, brain and sleep
What is the vagus nerve? The gut’s direct line to the brain
The vagus nerve is the main nerve of the body’s ‘rest and digest’ system. It runs from the brainstem through the neck to the heart, the lungs and most of the digestive tract. Most of its fibres carry information upward, from the organs to the brain. It slows the heart, drives digestion and helps to restrain inflammation. Slow breathing, exercise and good sleep are the simplest ways to keep it working well.
In short
- The vagus nerve is the longest of the nerves that arise directly from the brain.
- About four-fifths of its fibres are sensory: they report the state of the gut and other organs to the brain.
- It is the main channel of the gut-brain connection.
- Its activity can be estimated from heart rate variability, and it responds to breathing, exercise and sleep.
Where does the vagus nerve go?
“Vagus” is Latin for wandering. There is one on each side. From the brainstem they pass down the neck beside the large blood vessels, give branches to the throat and voice box, the heart and the lungs, pass through the diaphragm, and spread over the stomach, small intestine, liver, pancreas and the first part of the colon.
What does it do?
For digestion
It triggers the release of stomach acid and digestive enzymes, makes the stomach relax to receive a meal, sets the pace of gut movement, and makes the gallbladder contract.
For the heart and lungs
It slows the heart rate and helps to regulate breathing.
For appetite
It carries signals of stretch and fullness from the stomach to the brain.
For inflammation
Through a reflex known as the inflammatory reflex, it signals immune cells to reduce their output of inflammatory substances.
For the gut-brain connection
It conveys information about the gut, including signals influenced by gut bacteria, to the parts of the brain that handle mood and stress.
What happens when it is not working well?
Nerve damage, most often from long-standing diabetes or from surgery on the stomach or food pipe, causes slow stomach emptying, with fullness, nausea and vomiting.
Far more common is reduced vagal activity without nerve damage, as part of long-term stress, poor sleep and inactivity. It is associated with a faster resting heart rate, slower recovery after stress and a more sensitive gut, as seen in IBS. There is no single symptom that proves it.
How is vagal activity measured?
Indirectly, through heart rate variability (HRV): the small, beat-to-beat changes in the interval between heartbeats. Higher variability at rest generally reflects stronger vagal activity. In my practice, a short HRV recording is used as a starting point for breathing and biofeedback work. Readings from consumer wearables are useful for following your own trend, not as a diagnosis.
What supports the vagus nerve?
- Slow breathing, about six breaths a minute, with a long out-breath
- Regular physical activity
- Seven to eight hours of sleep at consistent times
- Humming, chanting and singing, which vibrate the throat where the nerve has branches
- Yoga and meditation
- Good company and laughter
What is vagus nerve stimulation?
Devices can stimulate the nerve electrically. Implanted devices are used by neurologists for epilepsy and depression. Non-invasive devices held against the neck are used for migraine and cluster headache, and are being studied in gut conditions. See vagus nerve stimulation therapy.
When should I see a doctor?
See a doctor for repeated vomiting, early fullness with weight loss, fainting, a persistently fast or irregular heartbeat, or a hoarse voice with difficulty swallowing. These need assessment and are not managed with breathing exercises.
Questions patients ask me
Can I feel my vagus nerve?
Not directly. You can feel its effects: the heart slowing as you breathe out slowly, or the calm after a long exhale.
Is the vagus nerve the reason stress upsets my stomach?
Largely, yes. Under stress the “fight or flight” system takes over and vagal activity falls, so digestion slows or becomes irregular.
Can gut bacteria talk to the brain through the vagus nerve?
Animal studies show that some effects of gut bacteria on behaviour disappear when the vagus nerve is cut. In people this is an active area of research.
Does a low HRV mean something is wrong?
Not by itself. HRV varies with age, fitness, sleep and illness. A falling trend in your own readings is more informative than one number.
Sources
This page is written for patients and is based on the guidelines and studies below. It is for education and does not replace a consultation.
- Review of the vagus nerve in the microbiota-gut-brain axis. Bonaz B et al. Front Neurosci. 2018. PubMed 29467611
- Review of the microbiota-gut-brain axis. Cryan JF et al. Physiol Rev. 2019. PubMed 31460832
- Review of the enteric nervous system. Furness JB. Nat Rev Gastroenterol Hepatol. 2012. PubMed 22392290