Stress, physical health, mental health

I've long been interested in the relationship between emotional stress and physical illness. I was fascinated to read an article in this week's Science News about the relationship between stress, the immune system, inflammatory illnesses, and depression. Apparently, over the past five years, a new line of research has been opened up by research into a new drug: this immune-boosting chemical causes major depression in up to half the patients taking it.

For many years, the prevailing wisdom has held that when a person is sick or injured, their immune system uses energy to fight the infection or in healing processes. The body then has an energy deficit, and a person feels tired. Makes sense to me.

But it turns out it's the other way around: if the immune system feels it will be needed, it sends signals to the brain causing depression. The depressed person doesn't do anything energetic, thus freeing up energy for the immune system to use. This pre-injury immune rev-up gave an evolutionary advantage to animals that were likely to be injured shortly after experiencing a stressful situation: being chased by a tiger was the example given in the article.

However, in an environment where stress is unlikely to be related to physical injury (being yelled at by the boss was the example), this response is no longer advantageous. Not only that, but in the absence of physical injury the inflammatory immune response (which also helps with healing) causes physical illnesses such as psoriasis.

I think this is the first time a major mechanism for stress-related illnesses has been identified. This research is also pointing to identification of a distinct form of depression: Major Depression Disorder with Increased Inflammation may be added to the next edition of the DSM.

It's very nice to have a confirmed physical link between what goes on in one's head and what happens in one's body - nothing is really "all in the head". Hopefully understanding these conditions will lead not only to better treatment, but to a more serious societal attitude toward stress-related illnesses.