Playing in dirt is good for kids

Smarter, less anxious: study; Outdoor learning experiences and school gardens help students relax and learn better, researchers suggest

By SHARON KIRKEY
Canwest News Service
May 25, 2010

Parents, here's another reason for your kids to play outdoors in the dirt: It might make them smarter.

And, as a side benefit, dirt appears to be a natural anti-anxiety drug, but without the side effects.

Mice exposed to a bacterium found in soil navigated a maze twice as fast, and with less anxiety, as control mice, in studies presented yesterday at the 110th general meeting of the American Society for Microbiology in San Diego.

The researchers say we've become so urbanized we risk losing a connection with an organism in nature that may actually be beneficial to humans.

Dr. Dorothy Matthews became intrigued by Mycobacterium vaccae - a natural soil microbe - in 2007, when British scientists published a study showing that when mice were injected with a heat-killed version of the organism, it stimulated neurons in the brainstem to start producing serotonin.

"Serotonin is a molecule that has a number of different effects, but one of them is modulating mood and decreasing anxiety," says Matthews, an associate professor of biology at The Sage Colleges in Troy, NY.

Serotonin also plays a role in learning. "If you're nervous, if you're frightened, you just can't think straight," Matthews said. She wondered, could M. vaccae have an effect on learning in mice?

The bacteria-exposed mice consistently ran the maze twice as fast as non-exposed mice. They also showed fewer anxiety behaviours - less freezing, wall-climbing, stopping and grooming, returning to the start, or defecation.

After the bacteria were removed, the mice started running the mazes slower than they did when they were ingesting the bacteria. "They experienced a kind of serotonin withdrawal," Matthews said. They were still faster than the controls, on average, an effect that lasted for another month of testing.

Matthews says people are exposed to M. vaccae just by virtue of being outdoors. "It's only been the last 100 years or so that we've become more urbanized and are eating our foods in a different way."

We no longer eat foods that we grow or gather ourselves, she says - foods that haven't been "washed multiple times, and dunked in hot water, or processed or grown with pesticides."

Making time in school curriculums for children to learn outdoors might decrease their anxiety and improve their ability to learn new tasks, she says.

"There's a movement now in some schools to actually have gardens that are part of the school experience."

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