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Stress, the vagus nerve, and the gut-brain connection

Ever wondered why you feel nauseous when you're anxious, or get an upset tummy when stressed?

Neurogastroenterology is a fairly new area of medicine, that focuses on the gut brain connection - how our nervous system affects the gut and vice versa

The gut has its very own nervous system, the enteric nervous system (ENS) - its like a second brain that runs through the gut wall!

This contains 200-600 million neurons (nerve cells) - as many as the spinal cord - and has more nerve cells than any other organ outside the brain!

The ENS is connected to the brain via the vagus nerve and the gut brain axis, which send signals back and forth between the gut and brain

This means thoughts, feelings, and memories can affect the gut, and our gut health affects our mental health, brain function, and stress levels

The gut brain axis consists of :

- the vagus nerve

- neurotransmitters

- the bacteria that live in our gut

The ENS controls many functions of the gut, including :

- gut wall integrity (ie stopping leaky gut)

- secreting digestive enzymes (to digest food)

-motility (gut muscle contraction to move food through the digestive system)

- blood flow and fluid absorption in the gut

- neuroendocrine production ( serotonin, opioids, dopamine etc )

- immune defence

-monitoring and regulating acidity levels in the gut

- it even influences our gut microbiome!


The brain sends signals through the vagus nerve to control gut function

(gut muscle activity, digestive enzyme secretion)

Stress signals also go through the vagus nerve and can alter gut function - reducing digestion, increasing pain, and causing symptoms like bloating and diarrhoea

The vagus nerve also sends signals from the gut to the brain - gut function and hormone levels appear to impact on mental health and brain health even though these hormones cannot cross the blood brain barrier

The vagus nerve affects the gut by :

- reducing intestinal permeability (aka leaky gut)

- stimulating release of digestive enzymes and stomach acid (helping digestion)

- stimulating peristalsis (gut muscle contractions, which move food through the digestive system. This reduces bloating, constipation and nausea)

- improving gut microbe diversity and short chain fatty acid production (protects gut lining among many other roles)

-reducing gut inflammation


The brain also sends neurotransmitters to the gut via the vagus nerve, to control function

Serotonin (happy hormone) is one of the main ones - 95% of the body's serotonin receptors are in the gut!

This affects gut muscle function, digestion, and pain.

Many of the symptoms of IBS are thought to be due to altered serotonin levels - helping explain the connection between ibs and depression /anxiety/stress

The gut also produces its own serotonin which may also travel back up the vagus nerve to impact on mental health

The gut even produces its own neurotransmitters and hormones - serotonin (happy hormones), dopamine (feel good hormones) and opioids (pain relief)!

People with IBS can have an elevated response to stress which often contributes to symptoms, and explains partly why stress is such a common trigger for symptoms - in one study cortisol levels we

re far higher in IBS patients than in people without IBS when stress occurred, this cortisol may contribute to gut symptoms


the gut microbiome also plays a big role in vagal nerve function and how stress affects the gut

In mouse studies, improving gut bacteria improves blood levels of cortisol, serotonin, and GABA

Probiotics, prebiotic, and high fibre diets also improve stress, depression, and anxiety, as well as IBS symptoms in some trials.

When the vagus nerve is cut this effect often disappears, suggesting the vagus nerve helps transmit signals from the gut microbiome to the brain 😊


The mind - gut connection is very real, and managing this is a vital part of holistic health

The ENS plays a central role in many gut issues, ie IBS, IBD, reflux, coeliac disease, and indigestion, as discussed above

As a result, stress can have a huge impact on the gut, via:

- increasing gut wall permeability

- damaging gut microbiome

- altering gut motility (causes cramps, indigestion, constipation, reflux or diarrhoea)

- reducing the protective lining of the gut (which can cause stomach ulcers and inflammation)

- slowing digestion (causes nausea, bloating )

- increasing stomach acidity (causing reflux)

Studies looking at the vagus nerve and gut, range from external vagus nerve stimulation, to the effect of diaphragmatic breathing on reflux, to how it alters the gut microbiome

Improving vagal tone and parasympathetic nervous function is therefore an important part of gut health!

Ways to improve vagal function and reduce the effects of stress on the gut include:

- diaphragmatic slow breathing (one of my favourites, this also relaxes abdominal muscles, 'massages' the gut, and strengthens the diaphragm, helping with reflux, pain, bloating, and digestion )

- yoga (in particular yin yoga and restorative yoga)

- meditation (see posts on this for more detail)

- exercise, especially slow controlled exercise such as tai chi, and exercise in nature

- adequate sleep

- psychology input such as CBT

- gut directed hypnosis (Monash university has an excellent app called Nerva that teaches this)

- chanting /humming /singing

- probiotics such as lactobacillus and bifidobacteria (although research is still limited)

-a plant predominant whole food diet high in fibre, prebiotic foods, polyphenols, and fermented foods, with a big diversity (ie eat a rainbow) and adequate omega 3

- cold water exposure (again limited research, but stimulates the vagus nerve)

Front. Neurosci., 07 February 2018 |

The Vagus Nerve at the Interface of the Microbiota-Gut-Brain Axis

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