First lets explain that there are two forms of stress, acute and chronic or long term stress.
Acute stress is any specific stimulus (anything can cause this, e.g. sprint for bus, sudden fright, catching a falling glass etc) which triggers our “fight or flight” response. This process activates our nervous system, preparing our bodies to deal with the perceived danger, and is a totally natural and healthy reaction. Once the danger or stimulus has passed, normal function resumes, and everything is back to normal.
The problem occurs when this mechanism is constantly activated over a period of time, and does not reset back to normal, and is known as chronic or long term stress.
Factors responsible for this consistent over activation are unique for each person, and each may present with contrasting difficulty to bring these factors under control, but examples include:
- Emotional upset (e.g. bereavement, work or relationship problems, early life trauma)
- Modern fast paced lifestyle (e.g. work long hours, multiple children, studying)
- Excessive exercise regime
- Poor nutritional content of diet
- Regular high intake of stimulants (e.g. caffeine, nicotine, recreational drugs, sugars)
- Lack of sleep or poor sleep patterns (can be a cause of stress and stress can cause lack of sleep!)
- Genetic polymorphisms or predisposition to poor stress handling
- Combination or all of the above
These and many other factors may cause you to be under persistent chronic stress, but how does this cause a decline in digestive function and epithelial tissue (intestinal) permeability?
Well as always its not just one thing, takes time to develop, and its contributing mechanisms and rate of progression, are unique for us all. However there are several physiological dysfunctions that chronic stress may evoke, which when acting together, may eventually prove detrimental to our long term health.
Stomach Acid Decline
Stress causes the persistent activation of the sympathetic branch of the nervous system, to allow the body to deal with the perceived stressor.
However, the digestive system is controlled by the opposing arm, called the parasympathetic branch. The two sides work in tandem, but when one side is continually activated, the opposing systems function is switched off.
Therefore, periods of long term stress cause digestive function to decrease because the parasympathetic response is turned down, which in turn reduces both stomach acid quality & production, and therefore also affects nutrient digestion. (1)
This is particularly relevant for epithelial tissue integrity (intestinal cell wall), as the availability of certain proteins (and other nutrients) needed for its continued function, may be reduced due to a decline in stomach acid function.
Motility is the rate at which food is transported through the digestive system, and is regulated by a process called peristalsis.
Peristalsis is reduced during stress, which causes undigested food to ferment in the digestive tract.
If this continues over time, then it will affect the composition of the host microbiome (bacterial content) in both the small & large intestine, which creates an environment for pathogenic bacteria to flourish, known as bacterial dysbiosis. (2)
The rate of both dysbiosis progression & motility is also greatly influenced by the nutritional content of the host diet & the quality of stomach acid production.
Dysbiosis is not exclusively related to bacteria alone, and can include overgrowth of yeasts & parasites too, with its development exerting a profound influence on many body systems.
Dysbiosis leads to a decline in the integrity of the intestinal wall by stripping away its natural protective mucus layer. (3)
This allows pathogenic bacteria to cling to the wall, which in turn affects its digestive function whilst also scrambling the interconnected workings of the local immune, nervous & endocrine systems.(4)
Pathogenic bacteria also produce a substance called LPS (Lipopolysaccharide) which in the right environment (e.g. prolonged stress, dysbiosis, intestinal permeability) leak through into the blood stream, causing a wide range of seemingly unrelated symptoms.(5)
Immune System Dysfunction
As the effects already described accumulate over time, the local immune function of the gut begins to become dysfunctional. This is a complicated mechanism of development, but eventually leads to an increase in allergic reactions or intolerance to substances that are normally tolerated better (e.g. gluten, dairy etc).
There is also the danger of the immune system losing self tolerance when exposed to continuing stress, which is known as autoimmunity, and is what happens in diseases like Type 1 Diabetes, Multiple Sclerosis and Rheumatoid Arthritis.(6)
When the immune system becomes over activated, a state of chronic inflammation exists, which is the immune systems reaction, rightly or wrongly, to remove the increasing dangers it perceives. Inflammation eventually causes the tight junctions in epithelial tissue cells to lose their integrity.(7)
This is what leads to the condition known as intestinal permeability or “leaky gut”, and through the myriad of progressive dysfunctions described, is profoundly affected by periods of chronic or long term stress.
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1. Esplugues JV et al. Proc Natl Acad Sci USA 1996 Dec 10; 93(25): 14839–14844.
2. Giovanni B et al. Am J Gastroenterol 2005 Nov;100(11):2560-8
3. Mahesh S Desai et al. Cell. 2016 Nov 17; 167(5): 1339–1353.e21.
4. Antoni MH. Brain Behav Immun 2003;17:84-91
5. Fuke N et al. Nutrients 2019 Oct; 11(10): 2277.
6. Dhabhar FS. Allergy, asthma and clinical immunology 2008, 4(1):2-11
7. Buddenkotte J, Steinhoff M. Allergy. 2010;65:805–821