8 December 2010
Hygiene Hypothesis linked to depression
by Kate Melville 
Rates of depression in younger people have steadily grown to outnumber rates of depression in older populations and researchers think it may be because of a loss of healthy bacteria contributing to an inflammatory response in the brain. Emory University professor Charles Raison and other neuroscientists explore the possible link between cleanliness and depression in the current issue of the Archives of General Psychiatry. Their hypothesis builds on other research suggesting that depression may be the outcome of an inflammatory response occurring in the brain. In an effort to pinpoint potential triggers that might lead to this inflammatory response, researchers are taking a close look at the immune system of people living in the Western World. Raison says there is mounting evidence that disruptions in ancient relationships with microorganisms in soil, food and the gut may contribute to the increasing rates of depression.
According to Raison's article, the modern world has become so clean; we are deprived of the bacteria our immune systems came to rely on over long ages to keep inflammation at bay. "We have known for a long time that people with depression, even those who are not sick, have higher levels of inflammation," explains Raison. "Since ancient times benign microorganisms, some times referred to as 'old friends,' have taught the immune system how to tolerate other harmless microorganisms, and in the process, reduce inflammatory responses that have been linked to the development of most modern illnesses, from cancer to depression." Experiments are currently being conducted to test the efficacy of treatments that use properties of these "old friends" to improve mental states. "If the exposure to administration of the 'old friends' improves depression," the authors conclude, "the important question of whether we should encourage measured re-exposure to benign environmental microorganisms will not be far behind." Related:
A biomarker for suicidal tendencies?
Our Love Affair With Depression
Do antidepressants work through personality change?
Inventing Illness
Dr. Raison discusses his hypothesis
Source: Emory University
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