Vagus nerve

Also called tenth cranial nerve, cranial nerve X.

Dr Chad OkayFounder, Suna Health

4 min read. Updated .

The vagus nerve is the longest nerve in your autonomic nervous system, running from the brainstem down through the chest into the gut. It is the main wire of the gut-brain connection. Around 80% of its fibres carry signals from gut to brain, not the other way around. Its tone influences digestion, heart rate, mood and inflammation.

What the vagus actually connects

The vagus is the tenth cranial nerve, also called cranial nerve X. It leaves the skull through the jugular foramen, runs alongside the carotid artery in the neck, then branches widely. It supplies the heart, lungs, stomach, liver, kidneys and most of the small intestine and the upper colon. Below the upper colon, the gut is wired by other nerves.

Why it is mostly an information cable

Around 80% of vagal fibres are afferent, meaning they carry information from organs to the brain rather than commands from brain to organs. The vagus is the brain's main listening channel into the gut. It picks up signals about food, gut bacteria, immune activity and stretch, and feeds them upstream to brain regions involved in mood, hunger and stress regulation.

Vagal tone

Vagal tone refers to how active your vagus is at rest. Higher tone is associated with a slower resting heart rate, greater heart rate variability (HRV), and a calmer parasympathetic state. Lower tone is associated with faster resting heart rate, lower HRV, and worse stress recovery. HRV measured by wearables is the most common consumer proxy for vagal tone, although it is not a direct measurement.

What the vagus does for digestion

  • Triggers stomach acid release before and during meals.
  • Helps drive the stomach's fasting housekeeping contractions. The small intestine's migrating motor complex is mostly run by the gut's own enteric nerves and the hormone motilin, not the vagus.
  • Slows the heart and lowers blood pressure during eating, the rest-and-digest state.
  • Influences the gut microbiome through stress signalling and gut motility.
  • Carries the satiety signals from gut hormones like CCK and GLP-1 up to the brainstem.

Things that support vagal tone

  • Slow nasal breathing, around six breaths per minute.
  • Cold exposure, like a cold shower or face-in-cold-water dive reflex.
  • Humming, gargling or singing (the vagus runs alongside the larynx).
  • Moderate cardiovascular exercise.
  • Sleep. Sleep deprivation drops HRV and vagal tone reliably.
  • Time in nature, mindfulness practices, and slow eating.

When vagal function is impaired

Long-term diabetes can damage vagal nerve fibres, contributing to gastroparesis. Long-Covid, some autoimmune conditions and vagus nerve injury during neck or chest surgery can also reduce function. Implanted vagus nerve stimulators are used clinically for treatment-resistant epilepsy and some cases of severe depression.

Why it matters for the long run

The long-run interest in the vagus nerve is tone: the strength of its calming influence, which tends to decline with age and chronic stress and to hold up with regular movement, sleep and time spent genuinely unwound. Years of ordinary parasympathetic time, meals eaten slowly, walks, breath that isn't hurried, are the unglamorous maintenance plan for the gut-brain line.

Common questions

Can you actually measure your vagus nerve at home?
Not directly. Heart rate variability (HRV), measured by Oura, Whoop, Apple Watch, or a chest strap, is the most common indirect measure. Higher HRV during sleep usually means higher vagal tone. The relationship is approximate but useful for tracking trends in yourself.
Does humming actually stimulate the vagus?
There is evidence that vibration from humming, gargling and singing activates the vagal branches running near the larynx. Effects on overall vagal tone are modest in studies. It is not a substitute for sleep, exercise or stress management, but it does no harm.
What is polyvagal theory?
Polyvagal theory is a framework proposed by Stephen Porges that splits the vagus into ventral (calming, social engagement) and dorsal (shutdown, freeze) branches. It is widely cited in trauma therapy. Mainstream neuroscience considers parts of it speculative, though the underlying anatomy of the vagus is well established.
Can stress damage the vagus?
Acute stress reduces vagal tone temporarily, which is normal. Chronic stress reduces vagal tone for longer periods and is associated with worse heart rate variability and gut symptoms. Damage in the structural sense is unusual outside of specific medical events like surgery, severe diabetes or trauma.

Sources

Written by Dr Chad Okay. Contributor: Dr Parisah Hussain, MBChB, BSc (Hons), DRCOG, MRCGP. Last updated 15 September 2026. From Digests.

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