07 January 2015

Could depression really be caused by inflammation?

For many years, depression has been viewed as a mental health issue but new findings suggest that depression could be affected or even caused by the body's own immune response.


Is depression really a mental illness or could it be caused by a reaction in the body? While it may sound completely absurd, there is growing evidence to suggest that depression and other mental conditions such as bipolar disorder may actually be affected, or even caused, by inflammation in the body.

A recent article by the Guardian discusses the idea that depression may actually be an immune or allergic response occurring in the body. While depression may be the actual immune response, it is more likely that the depression results from the inflammation.

A study published in the Journal of Affective Disorders in 2009 found higher levels of cytokines in those suffering from bipolar disorder. Cytokines play an important role in immune and inflammatory responses in the body. This finding suggests a link between inflammation and mania or depression.

A 2013 study by Copenhagen University Hospital published in JAMA Psychiatry further indicates a link between inflammation and mental illness. After collecting data from 73 000 adults, it was found that those suffering from depression (taking antidepressants) where three times more likely to have high levels of C-reactive protein (CRP) in their blood. CRP is an important indicator of immune response in the body.

There is also evidence to suggest that taking non-steroidal anti-inflammatory drugs (NSAID’s) in combination with an antidepressant improves symptoms of depression. A study published in Molecular  Psychiatry in 2006 found that patients taking celoxib (an NSAID) in addition to reboxetine (a norepinephrine reuptake inhibitor antidepressant) showed a far more substantial decrease in depressive symptoms over a six week period than those taking only reboxetine. 

Chronic inflammation, inflammation lasting for months or even years, can take its toll on the body and has also been linked to a number of other conditions such as cancer and type 2 diabetes.

Read: Blood protein linked to depression

What causes the inflammation?

There are many different theories as to why and how the inflammatory response occurs. Some  believe that the inflammation in the body has to be caused by a virus and therefore think that a viral infection is responsible for causing depression. Dr. Turhan Canli, Associate Professor of Integrative Neuroscience at Stony Brook University in New York has gone so far to state that major depressive disorder (MDD) should be reclassified as an infectious disease.

Another theory, detailed in an article by Michael Berk et al for BioMed Central, suggests that environmental stress and trauma actually cause the increase in cytokines, leading to inflammation. This reaction may form part the body’s natural response to protect itself from the perceived threat. Prolonged exposure to stress or trauma can result in longer-lasting inflammation or even disorders associated with inflammation such as depression.

While various theories on the exact cause of the inflammation are yet to be proven, the idea that depression affects more than just the mind may actually help to reduce shame or stigma associated with the condition. Depression, anxiety and other mental illnesses are often considered to only afflict the "weak" who are, more often than not, told to toughen up, stop feeling sorry for themselves and to just get over it. Whilst such a stigma surrounding mental health issues should be eradicated, the idea that depression may begin with a physical change in the body may help the public to better understand that mental health deserves equal weight to other medical conditions.

Read more:
Causes of depression
Poor sleep linked to inflammation in teens
Too much sitting could cause depression

Image: Depressive young woman sitting in chair at home from Shutterstock


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Michael Simpson has been a senior psychiatric academic, researcher, and Professor in several countries, having worked at London University in the UK; McMaster University in Canada; Temple University in Philadelphia, USA.; and the University of Natal in South Africa.

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