Anyone familiar with the "hygiene hypothesis"? This theory proposes that by living in an ever-more-sterile environment, we have forced our immune systems to "look for something else to do," like causing asthma and an array of allergies, or attacking our islet cells, for example.
The theory goes that children who grow up exposed to multiple bacteria have stronger immune systems -- whereas the rising incidence of conditions like Type 1 diabetes, inflammatory bowel disease, multiple sclerosis and others may be, at least in part, the result of lifestyle and environmental changes that have made us too "clean" for our own good.
And now, the latest extension of this theory says that too little dirt may actually contribute to clinical depression (!) According to a recent report in The Economist, researchers at Bristol University in the UK experimenting with a treatment for lung cancer may have discovered a way to improve patients' emotional health by re-introducing some of the missing dirt. No kidding.
Doctors were inoculating patients with something called Mycobacterium vaccae, "a harmless relative of the bugs that cause tuberculosis and leprosy, that had, in this case, been rendered even more harmless by killing it." Patients inoculated with this stuff not only experienced fewer symptoms of the cancer, but also felt emotionally more healthy, more vital and sharper in a cognitive sense.
Now they're trying out the theory on mice. The hypothesis is that the immune response to M. vaccae induces the brain to produce serotonin (a molecule that acts as a neurotransmitter, or chemical messenger between nerve cells), that is typically lacking in people with depression.
So far, it has worked. The researchers now have stress-free mice! -- measured, in case you're wondering, by dropping them into a tiny swimming pool. Previous research has shown that unstressed mice enjoy swimming, while stressed ones do not. The mice treated with serotonin swam around enthusiastically.
The implications are big:
1) "It opens a new line of inquiry into why depression is becoming more common... No one suggests this is the whole explanation for depression, but it may turn out to be part of it."
2) "It offers the possibility of treating clinical depression with what is, in effect, a vaccination... Besides cancer, and now depression, it is being looked at as a way of treating Crohn's disease (an inflammation of the gut) and rheumatoid arthritis."
Since diabetes and depression often go hand-in-hand, we may have hit the jackpot here. Re-introduce bacteria into our lives and we might get better. Who knew?