That's right. A living organism that acts like a mood-booster on the human brain, increasing serotonin and norepinephrine levels and making people feel happier. It was accidentally discovered about 10 years ago, when Dr. Mary O'Brien, an oncologist at the Royal Marsden Hospital in London, tried an experimental treatment for lung cancer. She inoculated patients with killed M. vaccae, expecting the bacteria -- which is related to ones that cause tuberculosis and leprosy -- to boost their immune system. It did that, The Economist reported in 2007, but it also improved her patients' "emotional health, vitality, and general cognitive function." Later experiments with mice confirmed the bacteria's effects; the study was published in a 2007 edition of the journal "Neuroscience."
"These studies help us understand how the body communicates with the brain and why a healthy immune system is important for maintaining mental health," the mouse study's lead author, neuroscientist Dr. Christopher Lowry, said. "They also leave us wondering if we shouldn't all be spending more time playing in the dirt."
"We believe that prolonged exposure to [M.vaccae] from childhood could have a beneficial effect," he added.
It raises the intriguing idea of a future where doctors could treat clinical depression or Seasonal Affective Disorder with a simple vaccine (and possibly a future in which kids don't need quite so may baths). In the meantime, people seeking a bit of a boost may be able to find it in their own backyards.
In an article in The Atlantic this week, author Pagan Kennedy tests out the ultimate in eco-friendly antidepressants herself. "As I huff the soil, I have no way of knowing exactly how much M. vaccae is floating into my lungs -- or whether it's enough to change my mind," she writes. "But I sure can smell this compost."
We wouldn't recommend inhaling dirt, of course. But, come spring, we're looking forward to spending more time getting dirty.