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Dirty Secret

Have you ever driven through the countryside and caught a whiff of a freshly plowed field? I don’t know about you, but that earthy scent always makes me feel just a little happier. Part of what we might be smelling is Mycobacterium vaccae, a type of bacteria found in soil. Recent scientific research is digging up interesting facts about exposure to this dirt born microorganism.

About 30 years ago a British scientist named David Strachan proposed a controversial hypothesis which has since gained traction. He suggested that our modern world is a bit too hygienic and over sanitized and that we might be healthier if we were exposed to more germs rather than less.

This "hygiene hypothesis" became part of a much broader examination of microbiota and its effect on human health. Today we know that friendly bacteria might influence our physical health in many ways. For example, most of us have heard of pro-biotics and understand that these friendly bacteria help keep our gut healthy. Many of us are also aware that overuse of anti-biotics that kill harmful bacteria but also helpful bacteria, has led to a problem of anti-bacterial resistance.

Less well known are the ways that bacteria might affect our mental health. If we look at bacteria that populate our gut, we find that the friendly “pro-biotic” bacteria, as they consume dietary fiber, create chemicals that eventually increase the production of mood boosting hormones in the brain. There are also unfriendly bacteria in the gut that multiply when we consume too much sugar. That may be the reason that a link between excess sugar consumption and depression has been found.

But digestion of food is not the only way we take in bacteria and that brings me back to Mycobacterium vaccae. Part of David Strachan’s theory is that we don’t encounter as many friendly bacteria as we once did because we do not come in contact with the earth. By not walking around barefoot and digging in the dirt, we don’t absorb beneficial bacteria like Mycobacterium vaccae. Also very interesting is a recent study of Mycobacterium vaccae that looked at its positive effect on airway responsiveness and inflammation when it is inhaled. This therapy may one day be used to treat people with asthma.

And all of this may explain in part why time spent outdoors breathing fresh air and pursuing activities like gardening and jumping in mud puddles, can be so beneficial to our mental well-being!

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