Guess We'll Just Go Eat Dirt

And be happy about it:

Exposure to friendly soil bacteria could improve mood by boosting the immune system just as effectively as antidepressant drugs, a new study suggests.

Researchers exposed mice to a harmless soil microbe called Mycobacterium vaccae and had the rodents perform a behavioral task commonly used to test the efficacy of antidepressant drugs.

The mice were placed in a large beaker of water for five minutes and watched to see how long they continued swimming and searching for an exit before giving up. The researchers found that the bacteria-exposed mice continued paddling around much longer than the control mice.

....Scientists think the lack of serotonin in the brain is thought to cause depression in people.

Previous studies have linked early childhood exposure to bacteria to protection against allergies and asthma in adulthood. The new finding take this idea, called the “hygiene hypothesis,” a step further, and suggests bacteria-exposure not only boosts our immune systems, but alters our vulnerability to conditions such as depression as well.