The answer is yes, there is a connection between the gut, your brain and chronic pain. Around 2 billion people are living with chronic pain worldwide.[1] For most people living with chronic pain, it is often considered a symptom of another condition. Usually, unfortunately, this leaves it inadequately treated.
In my early years of practice, I saw many fibromyalgia patients, and from my point of view, the level of debilitation is second to none. One of the critical facets I witnessed then almost fifteen years ago and more so today is the need for a multidisciplinary approach to chronic pain management.[2]
This multidisciplinary approach refers to psychological and social support networks, not just pills and potions to appease the symptoms.
In 2022 and beyond, this multidisciplinary approach for chronic pain now seems to entail a multi-system intervention with the gut-brain axis as a central figure. This intervention is by mitigating body-wide inflammation via remedying what’s commonly known as leaky gut, or the direct influence bacteria of the microbiome have on pathways that regulate and create inflammation.
Wait, there is a connection between the brain and my digestion?
Not just a connection, more like a superhighway. So much so that the enteric nervous system, located in the digestive system, has a similar neuronal composition (around 200-600 million neurons) as the spinal cord.[3]This similarity has led to the enteric nervous system’s nickname the “second brain.”[4]
This superhighway runs both ways too. The digestive interacts with and, in some cases, creates its own brain chemicals. Furthermore, the brain directly influences blood flow and the journey your food takes through the digestive system and out of the body. A process called motility. The central nervous influences the immune system’s activity in the digestive system.[5]
Even the western diet, which is well-known to affect the microbiome, has been shown to affect cognition and working memory in mice.[6] While only an animal study, I often see this clinically in humans. As soon as we change the diet’s energy allocation (if you get energy from protein, carbohydrates or fat), the brain seems to recover miraculously! This change is, of course, without using any nootropic formulas, just diet and some probiotic work.
Probiotics bacteria in the digestive system are central to the connection between digestion and the brain.
Probiotic bacteria can produce their unique versions of neurotransmitters such as serotonin and GABA.[7]
But wait, there’s more. Specific probiotic strains such as Lactobacillus rhamnosus have reduced subjective anxiety scores in healthy subjects in just four weeks.[8] This study was published eight weeks ago, showing how early this research is in humans.
Another study from 2021 also showed that probiotic changes in the microbiome are beneficial for cognition, especially working memory changes caused by stress.[9]
So, we know the gut affects the brain, but how does the brain affect chronic pain?
Ok, so you caught me. I’m trying to be a poet, and I know it.
Let’s bring the brain and the genesis of pain together. There are a few different types of pain; for this article, we will be looking at chronic pain. Chronic pain, by definition, is persistent or recurring pain lasting over three months, often associated with another condition, such as irritable bowel syndrome (IBS) or osteoarthritis.[10]
More comprehensive definitions segment chronic pain into different categories, including nerve pain and pain associated with cancer[11] , but we won’t go into the specifics here for simplicity.
The pathway signals of distress travel from the site of damage to the spinal cord, where they then travel up to the central nervous system or the brain. The brain develops the pain intensity and the subsequent reaction to these signals. The response is then communicated back through the nervous system.[12]
Pain perception depends not only on physiological processes but also on psychological, emotional, and behavioural ones. Emotional and attention-based regions of the brain have been measured, highlighting the interaction between paying attention to pain and the intensity of the pain experienced. This interaction has led to a direct relationship between higher levels of vigilance and pain intensity.[13]
This interaction between attention and pain is just one example of how the brain plays a role.
There are many more, including how you respond emotionally and if you have memories of previously painful experiences. Both of which can amplify the intensity of pain. Even a negative emotion can release pro-inflammatory chemicals amplifying pain.[14]
The psychological elements negatively affecting pain intensity could be an article unto itself but let’s bring back the triad of the gut, brain and chronic pain together.
As we touched on above, the microbiome can influence the brain or central nervous system through multiple pathways. The majority of these are through to the metabolites it produces.
If you are new to the term metabolites, these are small molecules which are the end products of a metabolic process—a process that either builds something or deconstructs something.[15]
Hope I’ve explained that ok; it’ll help you understand how the gut influences pain.
When the bacteria in the gut go through a process that either build something or breaks it down, the products produced at the end of that reaction/process are the ones that influence the central nervous system.
One of the more interesting ways these metabolites influence the central nervous system is via their immune cells within the brain called microglia. Microglia are immune cells connected to the regulation of brain diseases such as Alzheimer’s disease, Parkinson’s disease, Huntington’s disease, multiple sclerosis, stroke, not to mention anxiety and depression.[16]
Now, whilst this area of research is still in its infancy, or at least it seems this way to me, the microglia can influence the amount of inflammation created in response to an injury. This influence extends to how sensitive the surrounding areas of the nerves are to the same pain, potentially sustaining the pain response and extending it well beyond the initial site of the injury.[17]
One of the fascinating parts of all this is that recently inhibiting microglial activation can result in positive changes in pain within minutes to tens of minutes. This positive change has only been achieved in animals but provides a starting point to build on again.
The messages from the metabolites created by the bacteria in your gut are fundamental to helping the microglia cells grow and thrive in early life.[18]
The ability of the gut bacteria’s metabolites to influence the immune system in the brain is only part of it. Animal studies have shown that antibiotic use early in life affects the microbiome in such a way that the changes can contribute to longer lasting visceral pain.[19]
Furthermore, one before-clinic study showed that early life gut bacteria are integral in developing the stress response, [20] a crucial influence on pain sensitivity, especially when it comes to visceral pain. It’ll be interesting to see how these animal studies carry over into human studies. Let’s get back to one of the most common forms of chronic pain, visceral pain.
Why is visceral pain significant?
Visceral pain is the type of pain that most people seek medical attention for and is also the most common form of pain produced by disease.[21] Visceral pain is a deep, dull, vague sensation, often located around the abdomen and challenging to describe.[22]
Sounds familiar? If you have irritable bowel syndrome or IBS, you’ll be used to this sensation. It’s one of the most debilitating parts of most presentations of IBS.[23]
Because of this, we then see a logical move towards studies investigating how influencing the microbiome can positively affect visceral pain, including pain sensitivity. A significant part of the psychological recovery post clearing the initial physical IBS symptoms.
The microbiome’s ability to influence serotonin production affects your experience of chronic visceral pain.[24]
The microbiome’s effect on serotonin is possibly one of the clearest examples of how the brain and the gut influence the experience of chronic pain. If you are new to what it does in the body, serotonin affects digestion and mood, sleep, appetite, memory, and learning.[25]
Interventions that affect serotonin, such as SSRI antidepressant drugs, have been successfully used to treat pain conditions such as migraine and chronic visceral pain in functional digestive disorders such as IBS.[26]
Changes in serotonin levels, especially when they are low, along with the amino acid that builds serotonin, tryptophan, have been shown in humans to increase pain and urge scoring in IBS.[27]
Why does serotonin, a chemical we know affects the brain so much, have such an effect on digestion?
The answer is simple. Over eighty per cent of the serotonin is in the digestive system.[28]
Furthermore, gut bacteria play a significant role in whether or not a sufficient amount reaches the brain.
But what about other forms of pain, such as the inflammatory pain of osteoarthritis?
More studies on humans are required to see precisely which species or strains of probiotics work and how long you need to take them. However, a systematic review, one of the higher standards of assessing research, looked at twelve studies relating to probiotics and their role in inflammatory forms of arthritis such as osteoarthritis and rheumatoid arthritis.
The results showed a statistically significant reduction in the inflammatory marker C- reactive protein, commonly used for rheumatoid arthritis. Typically, the probiotic formula used in the studies had a combination of Lactobacillus and Bifidobacterium for sixty days.
Another study looked at Lactobacillus casei specifically in rheumatoid arthritis and found an improvement in inflammatory status over eight weeks.[29]
Do we know how probiotics improve inflammation?
Simply put, it seems that some probiotics trigger an anti-inflammatory chemical that balances out the activity of the chemicals causing the initial inflammation.
Cytokines are molecules whose job is to create inflammation to assist the immune system in activating when needed. Or at least that’s my effort at simplifying their role!
In contrast, whilst there are inflammatory molecules, the body also has ways to calm these cells down, and it does so using a cytokine called interleukin-10. Probiotics, mainly from the Lactobacillus strains, can activate higher levels of interleukin-10. This ability means that certain probiotic strains control the on/off switch of the immune activity responsible for some of the pain you’re experiencing.[30]
In conclusion, the gut influences the brain and the gut and the brain influence chronic pain.
Clear as mud?
In summary, we’ve seen in this article that the gut and brain connection is an essential component of chronic pain. Both in origin, intensity and the way you experience chronic pain.
Whilst metabolites (see above for the definition if you’ve forgotten) can make things worse pain-wise, we’ve also hopefully seen that probiotics can also improve the often imbalanced inflammatory pathways. The same pathways leave people living with chronic pain either in the form of visceral pain from IBS or inflammatory pain from the different conditions of arthritis.
And this only touches the tip of the iceberg. As the research on how influencing the gut-brain connection assists with chronic pain in all its forms unfolds, we’ll see the full potential of how to help people who are currently looking for answers for their chronic pain conditions.
Hope this helps.
References
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