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, cooking.net">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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