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The Vagus Nerve
The vagus nerve is one of the longest nerves in your body and a key component of your parasympathetic, or rest and digest, nervous system.
Research into the vagus nerve is ongoing and there is still much to learn, but many connections have been made between its proper functioning and IBS.
Find out more about the vagus nerve and it's possible connections to IBS...
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What is the Vagus Nerve?
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The vagus nerve, also known as the 10th cranial nerve or the vagal nerves, is actually a pair of nerves with similar functions. A left and a right vagus nerve start from the brainstem on each side of your body and go all the way to your large intestine, connecting with your esophagus, heart, lungs and parts of your GI tract. It's one of the longest nerves in your body and is named from the Latin for "wandering", because of the long and winding path it takes.
The vagus nerve is a key component of your parasympathetic nervous system (PNS). The PNS controls your “rest and digest” functions and helps to balance your sympathetic nervous system by counteracting its “fight or flight” responses. For a refresher on the nervous system and the stress response go to The Stress Response section.
The Mind-Body Connection
The vagus nerve is essential for communication between your brain and your body. It can influence bodily functions like heart rate, breathing and immune system response and conditions like mood disorders, anxiety and inflammatory diseases.
The vagus nerve is also a key component of the gut-brain axis. It's one of the main pathways for information to flow in both directions between the enteric nervous system in the gut and the central nervous system in the brain. Go to The Gut-Brain Axis for more info.
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What is Vagal Tone?
Vagal tone refers to the level of activity of the vagus nerve. High vagal tone is generally associated with beneficial effects like resilience to stress. A low vagal tone is associated with a reduced ability to cope with stress and various health issues. However, too much of a good thing can lead to problems as well. So, as usual, balance is key.
In research studies vagal tone isn't measured directly. Instead, it's estimated by measuring the vagus nerve's effect in controlling the pattern and timing of your heartbeats (heart rate variability or HRV).
Unfortunately, many factors can affect HRV, making it difficult to measure the actual activity of the vagus nerve. This in turn makes it difficult to interpret findings, compare results across studies and to fully understand the causal link between health outcomes and vagus nerve activity.
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The Vagus Nerve and IBS
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Research shows an association between IBS and low vagal tone. A low vagal tone has been associated with disrupted gut motility and increased gut sensitivity, both major symptoms of IBS.
In IBS, the vagus nerve may send incorrect signals or misinterpret information from the gut. And as a key player in the gut-brain axis, there are many ways that the health of the vagus nerve could be associated with IBS drivers and symptoms.
Digestion
For starters, the vagus nerve is essential for proper digestion. It regulates the release of digestive enzymes, gastric acid, and bile to break down food and controls the contractions of the stomach and intestines to move food through the digestive tract. If the vagus nerve isn't working properly, gut motility could be affected and lead to IBS symptoms like constipation and diarrhea.
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Regulation of Appetite
The vagus nerve is connected to two important hormones that regulate appetite and food intake. Leptin, known as the "fullness hormone," signals the body to stop eating and regulates fat storage and ghrelin, the "hunger hormone," stimulates food intake.
Studies have indicated that individuals with IBS often experience disruptions in the balance of hunger and fullness cues, which can lead to overeating or disordered eating patterns. This imbalance is associated with alterations in the hormones leptin and ghrelin.
For more info go to Disordered Eating and IBS.
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Stress Response
When you encounter a stressor, your sympathetic nervous system (SNS) kicks in and triggers a "fight or flight" response to help you deal with the situation. Then your parasympathetic nervous system (PNS) takes over and brings you back to "rest and digest mode". This is an ideal stress response. Since the vagus nerve is the main component of your PNS, it plays a large role in balancing your stress response.
However, if stress isn't managed well it can become chronic. When stress becomes chronic the fight or flight system is overactive and suppresses the vagus nerve's activity and calming influence, leading to a vicious cycle that can aggravates IBS symptom. A healthy vagal nerve, on the other hand, can aid in stress recovery.
To find out more about the impact of stress on IBS, go to Stress and IBS.
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Mental Health
A low vagal tone has also been linked to mood disorders like depression and anxiety. Chronic stress is a significant risk factor for these disorders and vagus nerve dysfunction may lead to improper stress responses.
IBS has also been linked to improper stress responses and mental health disorders.
Go to Mental Health and IBS to find out more.
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Inflammation
The vagus nerve helps to regulate inflammation in your body by communicating with various organs and the gut. In this way the vagus nerve plays a central role in your body's response to stress and disease. Low vagal tone can increase inflammation by reducing its anti-inflammatory effects.
Research is showing that chronic, low-grade inflammation of the inner lining of the intestines is involved in the disease process of IBS.
Go to Inflammation to find out more.
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Increased Gut Permeability
Inflammation can damage the inner walls of your intestines and cause your gut to become more permeable, allowing harmful substances to enter your bloodstream. In fact, the two conditions often create a vicious cycle. Harmful substances entering your bloodstream can further trigger inflammation.
The vagus nerve can influence gut permeability with its anti-inflammatory effects, as well as connections with the cells of the intestines and the gut microbiota.
Increased intestinal permeability has also been linked to IBS.
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The Gut Microbiome
The vagus nerve serves as a bridge linking your gut microbiota (the bacteria in your gut) and your brain. Gut bacteria produce substances that can be sensed by the vagus nerve, influencing brain function and gut health through the gut-brain axis.
Vagal tone, or the strength of vagal nerve activity, is associated with the diversity of the gut microbiome. It appears that a healthy vagal tone could promote beneficial bacteria and contribute to a more diverse and healthy microbiome.
Research is showing that communication between the microbiota, vagus nerve, and brain could influence IBS symptoms. Low vagal tone could lead to a less diverse gut microbiome and promote inflammation, which may contribute to the dysbiosis often seen in IBS patients.
To learn more go to About the Gut Microbiome section.
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Vagus Nerve Stimulation
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Vagus nerve stimulation (VNS) involves using a device to send mild and painless electrical impulses to the vagus nerve. The vagus nerve then relays these signals to the brain, causing changes to brain activity that may help calm irregular electrical patterns.
The main goal of VNS is to restore a normal vagal tone, including the anti-inflammatory properties of the vagus nerve.
There are two main types of VNS - invasive and non-invasive. An invasive VNS is implanted with two parts: a small, generator is placed under the skin in the upper chest and a wire goes under the skin to the side of the neck where it's coiled around the vagus nerve. There are newer, non-invasive vagus nerve stimulation devices that don't need surgery to implant the device.
VNS has been approved for the treatment of epilepsy and depression for decades. But it's also being investigated for the treatment of many other conditions, including IBS.
Vagus Nerve Stimulation and IBS
Due to its role in regulating inflammation, pain and the stress response, VNS is being investigated as a potential therapy for IBS. IBS is a disorder of gut-brain interaction and VNS is believed to restore stability to communication between the gut and the brain.
Some pilot studies have shown promising results. VNS has had some success in improving symptoms of IBS, especially when it's combined with lifestyle interventions like meditation and breath work.
Currently VNS is not a standard treatment option for IBS. More research is needed before specific recommendations can be made. However, this is certainly a space to watch.
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DIY Strategies
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These days it seems that everybody in the wellness community is talking about the vagus nerve and there seems to be a million ways to reset, activate, massage, tone and stretch it. However, many of these "sure fire" ways are not yet backed up by good research.
There are two ways to look at this. Just because science hasn't proved something, that doesn't mean it's not true. It's also harder to get money to study something that won't make someone some money. But if something isn't backed by science, then real recommendations can't be made. Be wary of claims that a certain strategy can "fix" or "rewire" your vagus nerve and all your problems will be solved!
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Studies on the vagus nerve are ongoing, so this is certainly a space to watch. Most evidence so far points to stress management, exercise and nutrition for a healthy gut microbiome as possible DIY strategies for improving the health of your vagus nerve.
As these strategies have also been associated with improving IBS symptoms and overall health, it's probably worth giving them a try anyway!
Follow the links to the relevant sections and check out a few strategies of note.
Go to Stress Management, Get Moving for IBS! and Food and Drink in the Gut Microbiome Health Strategies section.
Breathing Exercises
Some research shows specific breathing exercises, like diaphragmatic breathing, that emphasize slowed breath and/or longer exhalations (compared to inhalations) could stimulate the vagus nerve.
Stress management techniques that involve this kind of breath work, like meditation and yoga, may offer similar benefits.
Go to Breath Work to find out more.
Humming and Singing
Actions like humming, singing, and gargling engage the muscles at the back of the throat connected to the vagus nerve. The theory is that the resulting vibrations can stimulate the nerve, helping to calm the nervous system.
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Cold Exposure
Some studies have shown that brief exposure to cold, like splashing your face and neck with cold water or ending a shower with a minute of cold water, could stimulate the vagus nerve.
While more research is needed, the theory is that habitual cold exposure can enhance the activity of your parasympathetic nervous system (rest and digest) and decrease sympathetic (fight or flight) activity.
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