A study of more than 400 children diagnosed with Attention Deficit Hyperactivity Disorder has found a link between the children's routine play settings and the severity of their symptoms, researchers report. Those who regularly play in outdoor settings with lots of green (grass and trees, for example) have milder ADHD symptoms than those who play indoors or in built outdoor environments, the researchers found. The association holds even when the researchers controlled for income and other variables.

Previous research has shown that brief exposure to green outdoor spaces -- and in one study, to photos of green settings -- can improve concentration and impulse control in children and adults in the general population -- individuals without ADHD.

Kuo noted that the findings don't by themselves prove that routine playtime in green space reduces symptom severity in children with ADHD. But in light of all the previous studies showing a cause-and-effect relationship between exposure to nature and improved concentration and impulse control, she said, "it is reasonably safe to guess that that's true here as well."