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Why inflammation can cause anxiety

Anxiety and depression are two terrifying and seemingly uncontrollable monsters that many of us have or will experience in our lifetimes. For some of us, the burden of these has been so high that we require medical treatment and advice to cope and overcome them.

Medicine differentiates the causes into mental and physical. However, the label of "mental cause" has a profound negative effect on anyone that has to hear such words come out of the mouth of a physician. The message that it is given to us is often interpreted as "what you are experiencing at this moment is your own fault".

The stigma of a "mental cause" is so profound that many of us are inclined to believe that the symptoms of our depression and anxiety are all caused by our personality and it is a symbol of who we are. The impatience, anger, mood swings, irritability, the dreaded thoughts and emotions are all a product of our "defective" nervous system.

Other times we just refuse the notion altogether and firmly believe that due to the physician's incompetence to find a physical cause for our disease he simply labels us as "mentally ill" and is therefore done with the case.

Luckily, medicine has not been sleeping on depression and anxiety and has been thoroughly investing their underlying causes for years. Research has now firmly established that almost all mental and physical changes that occur during physical diseases are due to the actions of cytokines.

Inflammation and health

When our body is under any aggression, it's natural response is to secrete cytokines and therefore induce a state of inflammation. We've all heard of inflammation, and it is something we always associate with pain and disease. It is a state we try to abolish, yet our body intentionally enter an inflammation state to save your life.

During inflammation, as a response to cytokines, the body's immune cells surround the site of infection, or tissue damage, forming a protective film. This barrier prevents the infection from spreading to the rest of the body, thus keeping it localised. Before antibiotics were invented, an infection that managed to break through the immune wall quickly spread to the adjacent tissue and the bloodstream and would more often than not signal impending doom. Even in our modern era, an infection that the immune system is not able to contain is life threatening.

Cytokines and mental health

Now that we've established the important role of cytokines and inflammation in maintaining your health let us move on to how and why they influence our mental state.

Recent research on cytokines is slowly revolutionising our understanding of how this can affect our mental health. In addition to producing all of the signs and symptoms of a physical disease, cytokines have been shown to be able to provoke a wide range of mental health issues, including anxiety, depression and schizophrenia.

What is interesting still is that cytokines can also produce the physical signs that are usually associated with depression and anxiety, such as hormone disorders, inflammation, biochemical abnormalities, fatigue and headaches.

The usual assumption when considering the biological basis of psychiatric diseases is to look for the cause of it in the brain. However, recent research indicates that in many cases the culprit could very well be the immune system.

Cytokines have the ability to pass from the bloodstream into the brain. Additionally, they can also be secreted by immune cells that reside in the brain. Once in the brain, cytokines greatly influence the activity of neurotransmitters such as serotonin, norepinephrine and dopamine. This is of great importance, as an abnormal activity of these neurotransmitters is associated with depression and anxiety.

Research linking inflammation to depression

A team of researchers at Denmark's Aarhus University analysed the health records of about 3.6 million people in 2013 to find a link between inflammation and mental health disorders. They observed that people:

  • Suffering from autoimmune conditions that raised their inflammation level had a 45% greater chance of suffering from depression
  • Who had been hospitalised for a life-threatening inflammatory infection, had a 62% greater chance of suffering from depression

Numerous other research papers have tackled this subject and demonstrated that the presence of inflammatory messengers such as:

  • C-reactive protein
  • interleukin-6
  • interleukin-1
  • TNF-alpha
  • Cytokines

Are linked to an increased risk of developing psychological issues such as anxiety and depression.

Effects of inflammation on the brain

When cytokines enter the brain, they cause extreme changes in behaviour, mood and attitude. This is most evident when our body is fighting an illness, even the common cold. Many of us can relate to the feeling of fatigue, lack of interest in events and people and a depressed mood when battling the flu. While you might consider this normal, and a side effect of the obvious illness, it is actually caused by the action of cytokines in your brain.

This as well is one of our body's defence mechanisms. By making you feel terrible, anti-social and fatigued, your body is forcing you to rest, sleep and keep away from other people. Through this action, your body prevents the spread of disease to other people and also conserves the energy needed by the immune system to fight off the infection.

Conclusion

In an evolutionary sense, we can deduce that anxiety and depression are an innate defence mechanism. Since we have evolved passed the need to seclude ourselves to heal and prevent the spread of diseases, these symptoms are obsolete and a hindrance more than anything.

Luckily, due to this newfound link between inflammation and anxiety and depression, research also suggests that anti-inflammatory medication may be an effective treatment in some cases.

Editor's note

This article was written by one of our guest contributors. We don't 100% agree with the conclusion. Stress causes the body to release cytokines, which form part of the body's inflammation response. Therefore, it seems more likely that the anxiety causes the inflammation, or that a third confounding variable causes both.

Further reading

  • Wium-Andersen MK1, Ørsted DD, Nielsen SF, Nordestgaard BG. Elevated C-reactive protein levels, psychological distress, and depression in 73, 131 individuals. JAMA Psychiatry. 2013 Feb;70(2):176-84.
  • Smith RS. The immune system is a key factor in the etiology of psychosocial disease. Medical Hypotheses 34:49-57, 1991.
  • Smith RS, Maes M. The Macrophage-T-Lymphocyte Theory of Schizophrenia: Additional Evidence. Medical Hypotheses 45:135-141, 1995.
  • Smith RS. The macrophage theory of depression. Medical Hypotheses 35:298-305, 1991.

Metadata

Published 21 August 2017. Written by Alina Jensen.

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