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Children with Attention Deficit Hyperactivity Disorder (ADHD) who play outdoors among trees, grass and nature experience fewer symptoms, a new study shows.

The study, published in the journal Applied Psychology: Health and Well-Being, examined more than 400 children with ADHD. Those who played outdoors on a regular basis -- either directly in natural environments or in outdoor play areas -- experienced milder ADHD symptoms, the study concluded.

This is actually the latest in a series of studies looking at the effect of nature on kids with ADHD. Previous studies have shown short-term benefits of outdoor play (or even from looking at photos of nature), but the new study aimed to take it further. "Before the current study, we were confident that acute exposures to nature -- sort of one-time doses -- have short-term impacts on ADHD symptoms," co-author Frances (Ming) Kuo of the University of Illinois said in a prepared release. "The question is, if you're getting chronic exposure, but it's the same old stuff because it's in your backyard or it's the playground at your school, then does that help?"

The answer, it turned out, was yes. Symptoms of ADHD include difficulty concentrating, hyperactivity and poor impulse control -- all of which were experienced in lower levels by the children who played outdoors during the study.

The paper itself is available to the journal's subscribers. You can read the abstract here.