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Stress and Depression - the link.

The Immune Link


The human immune system and its response to stress, poor diet and toxins is becoming recognized as one of the key factors in chronic illnesses.  What is defined as the digestive tract? It starts with the mouth, travels down through the oesophagus to the stomach, from there to the small intestines and large intestines and ends with the anus.  The mucosal lining of the whole of this tract is the largest immune interface with the outside world and includes environment, food, bacteria and emotion.


Many conditions are now recognized to be affected by cytokines.  Cytokines are basically poly-peptide hormones and are the product of cells of the immune system. Sickness behaviour involves responses to an immune challenger eg stress, food, bacteria,  which promotes the release of pro inflammatory cytokines IL-1, TNFa and IL-6.  These cytokines have an impact on the hypothalamic/pituitary/adrenal axis and induce changes, like anhedonia (the inability to gain pleasure from pleasurable experiences), increased need for sleep, and other stress related disorders.  Depression may be a component of  sickness behaviour and alterations in immune function can affect personality traits producing extremes of emotions and other disorders. 




The digestive tract is affected by everything you eat, and more importantly, everything you think.  You may have heard the story of the Doctor in 1833 whose patient, a Canadian trapper called Alexis St Martin, who had a gun shot wound which would not heal and allowed for permanent observation of his gastric processes.  From this the good doctor was able to observe and record the psychological, physical and immunological stresses on his gastrointestinal tract.  It was fascinating to see the impact stress had on his patient’s guts. Now there are more sophisticated methods of observation, but this well documented case has been a cornerstone of the understanding of digestive diseases, and the impact of psychiatric disorders on the immune system function.


What many people fail to realise is that the digestive system is not only there to help us digest the food we eat, but serves many other functions as well. It is host to a colony of helpful (and sometimes not so helpful) co dependant bacteria, and most important of all, it is the site of the whole body’s largest collection of immune tissue.  The mucosal barriers of the intestines are not simply a first line of defense against unwanted bacteria or undigested food getting into our blood stream, they are also our defense against the stresses of the modern world.  Good gut health is literally our passport to greater health and well being, and stable mental health.


How does this happen?  Over thousands of years the bacteria that co exist within the lining of the bowels have developed highly specialized ‘skills’ to survive and modify the host body’s health through altering gene expression and function.  This mutual relationship is the most important and least understood aspect of integrated health care.


The small intestine is the area of most activity between the content of the gut, and the mucosa. 


To keep it simple, picture three different types of gut tissue and related substances: mucosa, lamina propria and the gut-associated lymphoid tissue (GALT for short). The lamina propria is home to specialized plasma cells and many other immune system components.  The GALT actually contains more immune cell elements than the bone marrow, spleen and lymph nodes combined. This immune system is like a surveillance mechanism that is finely tuned to protect the body from foreign matter such as bacteria and viruses, and so on.  Cytokines send signals to the brain via several mechanisms, including crossing the blood-brain barrier via the blood stream. They can also signal directly to the brain via the nerves.  This results in a MULTITUDE of connections with the abdominal organs.  The activation of the brain by cytokines from the gut induces anxiety, depression, mood changes, withdrawal from social situations,  and cautious avoidance associated with the stress response’s principal activity – maintaining the organism’s integrity during recovery from stressful activities or from traumatic injury. The discovery that cytokines affect the central nervous system in major depression is a good reason to implement cytokine mediated therapy.




Most people appreciate that serotonin is part of the feel good factor in our brains, but what few people appreciate is that of the total serotonin production, approximately 2% resides in the brain, 2% in the blood platelets, and a massive 96% is in the cells of the gut. 

Experiencing stressful event in one’s life, or bottling up emotion, can cause a massive amount of pro inflammatory cytokines to be released in response to the immune system triggers.  It is also thought that prior stressful experiences can sensitize individuals to future events.

As the gastro intestinal tract is the greatest site of immune tissue, disturbances to its eco system (eg through anti biotics), loss of tolerance and a reduction in the immune response will lead to the production of pro-inflammatory cytokines.  The physiological and psychological effects of immune activation (termed sickness behaviour) are then mediated by cytokines derived from activated immune response cells.




The use of natural agents like herbs and lactobacillus strains to improve anti inflammatory cytokine production and increase cortisol receptor  sensitivity as well as improving the function of the gastrointestinal tract, is a positive effect of Complementary and Alternative medicine.