Are depressed people too clean?

Rates of depression have steadily grown, and researchers think one cause may be the loss of healthy bacteria in today's cleaner, modern society.

In an article published in the Archives of General Psychiatry, Emory neuroscientist Charles Raison and colleagues reviewed the 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 the "hygiene hypothesis," 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,” Raison explains. “Since ancient times benign microorganisms, sometimes 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 emotional tolerance. “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.”


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