Health and happiness is all down to a roll in the dirt

"Forget the spring-cleaning. A study has found evidence that bacteria common in soil and dirt could improve people’s spirits.

According to the research, the action of Mycobacterium vaccae (M vaccae) on the brain is similar to that of some commonly used antidepressants.

The bacterium, which is related to the microbe that causes tuberculosis, appears to work by stimulating the body’s immune system. This, in turn, prompts certain cells in the brain to produce more serotonin, a hormone associated with feelings of wellbeing."

http://www.timesonline.co.uk/tol/life_and_style/health/article1596735.ece