Do you suffer from a nature-deficit disorder? Do you know someone who does? M. Sanjayan, Ph.D., lead scientist for The Nature Conservancy, as coined the term to describe a lack of interaction with nature. In one study, the farther you live from green space, the likelier you are to be in poorer health. A Japanese study found that people's blood pressure, resting heart rate, and levels of cortisol (a stress hormone) were all significantly lower after a 15-minute walk in nature as compared with a 15-minute city walk. Another study showed 37 percent spike in the number of natural killer cells—key immune system cells—after women spent a few hours out in the woods. The cure for nature-deficit disorder—not to mention a host of other ailments—might reside in a simple walk out in nature. Take time for one. Make time for one. It could improve your health.