“V” – Vagus Nerve: The Vagus Nerve and the brain-gut axis explained

What is the Vagus Nerve?

The Vagus (wandering) nerve (Cranial Nerve 10 – CNX), is the longest cranial nerve in the body. It originates from the brainstem, the part of the brain that controls automatic functions that are needed for survival. It travels down from the brain passing through the neck, torso and abdomen to reach most body organs.

The Vagus nerve regulates the balance between two parts of our autonomic nervous system – the sympathetic nervous system (SNS) responsible for the fight, flight, freeze response and the parasympathetic nervous system (PNS) which enables us to rest and digest. This constant state of balance (homeostasis) between the SNS and PNS systems is facilitated by communication via vagus nerve signalling between the brain and internal organs and biochemical messengers in the bloodstream.

The Gut-Brain Axis

The Vagus nerve connects the gut and brain via the Gut-Brain axis (GBA). It serves as a bi-directional “super-highway” along which approximately 80% of the information is sensory messages travelling from the organs to the brain (afferent fibres) ie: the vagus tells the brain what’s happening in your organs, and 20% is the response from the brain to the organs (efferent fibres) to regulate their functions.

The central and enteric (in the wall of the gastrointestinal tract) nervous systems, innate immune system, and gut microbiota all facilitate communication between the brain and the gut.

In the GBA the Vagus nerve innervates the tongue, pharynx, soft palate, oesophagus, stomach, gall bladder, pancreas, small intestine, and large intestine.

The Vagus Nerve influence on Digestion

• Digestion begins at the mouth: the vagus nerve increases salivation in response to the smell of food.

• In the gut, the vagus increases gastric juices, gut motility (movement) and balances stomach acid, pancreatic endocrine and exocrine secretion (enzymes and hormones), hepatic (liver) glucose production.

• Biochemical signals travel through the blood and via the vagus nerve. These biochemical messengers include neurotransmitters such as serotonin and glutamate, and gut hormones which communicate information from the gut to the brain. all of which play a vital role in sleep, mood, pain, stress and hunger. The neurotransmitters acetylcholine and GABA released in the brain, lower heart rate, blood pressure, and help your heart and organs slow down so that you can rest-and-digest.

• When food is eaten enteroendocrine cells secrete gut hormones, which send signals through the vagus nerve to suppress appetite when we are satiated (full). If vagal tone is low we are less able to regulate appetite and food intake. A reduced ability to respond to satiety hormones contributes to weight gain and obesity.

• The vagus nerve innervates most tissues involved in nutrient metabolism and has the potential to influence how nutrients are absorbed and metabolised.

• Migrating Motor complex (MMC) is a 4 phase cyclical process in which the body cleans out the digestive tract. The MMC is triggered by the vagus nerve and takes place 3-4hours after eating during “fasting mode”. (MMC is interrupted by eating, so it is best to space your meals by at least 3-5hours for the MMC to do its job of moving waste).

• The 4 phases of the MMC are:

  • 1: rest

  • 2: intermittent irregular contractions

  • 3: short bursts of regular high amplitude contractions

  • 4: rest

How do Microbes affect the Vagus Nerve?

• Gastrointestinal microbes directly stimulate the end terminals of the Vagus and are a key influence in the cross-talk between the gut and brain.

• Imbalances in the microbiome, including dysbiosis, pathogenic bacteria, fungi, parasites, viruses, leaky gut (increased intestinal permeability), IBS, and IBD, all cause inflammation which impacts the health of your gut and nervous system.

• Nerve Signals from the microbiota maintain the intestinal wall. When the microbiome is imbalanced it affects the integrity of tight junctions which may lead to leaky gut, food intolerances, chemical sensitivities and inflammation.

• Psychobiotics – probiotic strains known to influence the GBA, can improve the gut-brain axis and positively impact mood and behaviour.

• Disrupted gut function can also change the microbiota’s composition or metabolic activity.

Common causes of Brain-Gut axis dysfunction

• Psychological stress and trauma – Activate the Sympathetic nervous system to purposefully down regulate all digestive secretions, gastrointestinal motility, detoxification enzyme expression, immune function.

• When in a chronic state of stress, we are more susceptible to illness and it is more challenging to get and stay well.

• HPA dysfunction and sustained cortisol activity can lead to increased dysregulation in anti-inflammatory pathways (ie: inflammation persists and can cause chronic inflammatory conditions).

• Toxicity: Environmental, Chemicals, Smoking, Drugs

• Injury/ Physical trauma

• Disease/ Organ dysfunction

• Diet: Nutritional Deficiencies; toxic foods; intolerances and allergens increase inflammation

• Lifestyle: Poor sleep; insufficient rest.

What is Vagal Tone?

Good vagus nerve health is dependent on Vagal tone – the ability to switch between sympathetic nervous system activation in stressful events and to return easily to the parasympathetic state for regulating our nervous system.

Higher vagal tone means that your body can relax faster after stress, and can promote relaxation, sleep, digestion, and healing – you are more likely to recover quicker from injury, illness, and stress.

What causes Low Vagal Tone?

• Prolonged overstimulation of the nervous system can result in becoming desensitized to chronic stress and over time this can lead to low vagal tone.

• Low vagal tone has been linked to a variety of mental and physical health issues. including chronic inflammation, neurodegeneration, poor gut function – as it can stop your body from going into rest and digest; and autoimmunity.

What can I do to increase my Vagal Tone?

When the Vagus nerve is stimulated its tone increases (improves).

Below is a list of several ways to stimulate the vagus nerve: It is important to choose what is calming for YOU. Choose activities that enhance your state of relaxation, that you find calming and pleasurable as it releases oxytocin into your system, reducing stress and helping to improve mental and physical health.

Focus on your breathing.

• When you breathe deeply and slowly it signals to your brain that you are not in danger, which allows your nervous system to switch into a parasympathetic state, lower cortisol and activate higher levels of GABA.

  • Start gently, slow breathing, observe your breath: In via nose, out via pursed lips – extend exhalation as long as possible.

  • Diaphragmatic Breathing: Breathe into your diaphragm allow your belly to rise, hold it briefly, then exhale slowly.

  • Pranayama: Breathing exercises and patterns

  • Alternate nostril breathing

• Gargling 1 minute 2-3 x/day

• Yodelling

• Singing loudly

• Humming

• Laugh

• Chew gum

• Positive thoughts and positive self-talk: Reflecting on positive social connections improves vagal tone and increases positive emotions.

• Looking at something beautiful

• EFT; NET: Stress release techniques

• Meditation

• Spend time in nature, “nature bathing”

• Far Infra-Red Sauna

• Hot and cold plunges

• Cold showers – (finishing your shower with a cooler water temperature is a gentle way to begin the gradual transition to colder water for longer)

• Gentle exercise

Diet and Lifestyle to support the Gut-Brain Axis:

• Eat fibre: Eating fibre encourages the release of hormones that make it easier for the gut to send fullness cues to the brain via the vagus nerve.

• Sunlight: Exposing the skin to a safe amount of UVA light can produce a hormone (melanocyte stimulating Hormone – MSH) that improves vagus nerve function.

• Take Probiotics; Probiotics optimise gut-health. Specific strains of LGG may help the vagus nerve maintain GABA levels that have a calming and stress-relieving effect on our mood.

• Sleep: Better sleep quality is linked to high diversity of bacteria, lower inflammation and better mental health.

• Relieve neck tension and improve posture. Forward head posture puts more stress on your neck, thoracic spine and ribcage which affects breathing, diaphragm tension and digestion.

• Identify and treat underlying drivers of inflammation including dietary triggers; bacterial, parasitic and viral infections.

• Rebalance microbiome: supplementation with targeted probiotics

• Reduce intestinal permeability with individualised nutrients and dietary changes

• Support stress management

• Reduce inflammation

• Regulate the immune system

• Correct nutritional deficiencies with diet and individualised nutrient supplement support.

For a Healthy gut – healthy brain connection the Vagus nerve pathway must be intact with high vagal tone. To be able to ‘rest and digest’ and support the gut-brain axis we have to be in the ventral vagal state. It is our state of safety and homeostasis, a state that our bodies should be in 90% of the time.

To achieve that we need good nutrition, a healthy microbiome, restful sleep, time in nature, nurturing social connection, a sense of purpose, positive mindset, good posture, slow breathing and time to relax.

Disclaimer: The information written in this article is general in nature and does not constitute medical advice. For individualised treatments and specific nutritional advice please see your qualified healthcare professional.