Is depression really just an allergic reaction?
Depression has always been seen as a mental health concern, with relatively little known about biological causes, however some scientists are beginning to shed light on the subject.
George Slavish, clinical psychologist at the University of California in Los Angeles, has studied depression for years and has concluded that the condition has as much to do with the body as it does the mind.
"I don't even talk about it as a psychiatric condition any more.
"It does involve psychology, but it also involves equal parts of biology and physical health."
The basis of this new perception appears obvious once pointed out - everyone feels down when they are ill. The feeling of being fed up, bored and too tired when ill is known in the psychology world as 'sickness behaviour'. This happens for good reason to as it helps us avoid doing more damage to our bodies or spreading infection. It also resembles depression.
So, could there be a common cause linking sickness behaviour and depression? The most likely cause is inflammation - a reaction of the immune system when it is called to action to help fight infection. A family of proteins called cytokines set off the inflammatory response and interestingly cytokines and inflammation has been shown to increase when someone is suffering a depressive episode.
Healthy people have also been found to fall into temporary depressive states when given a vaccine that triggers inflammation. Brain imaging studies suggest that this may be due to changes in the part of the brain that processes punishment and reward.
Those who suffer from inflammatory diseases such as rheumatoid arthritis also tend to be more prone to depression than the average person. Turhan Canli from Stony Brook University in New York believes infections are most likely to blame and even thinks we should rebrand depression as an infectious (but not contagious) disease.
Other experts are not willing to go this far however, and many point out that infection is not the only way to set off inflammation. Obesity, high-fat diets and stress can all trigger inflammation as well.
With this in mind, it may be that prevention is the best place to start. A few clinical trials have found that adding anti-inflammatory medication to antidepressant medication improved symptoms and even increased the number of people who responded to the treatment. More trials will however be required to confirm these initial findings.
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