About 500 patients who visited a physician recently at Unity Health Care in Washington walked away with an unusual prescription.

The medicine? Regular doses of a local park.

The health system has a searchable database of more than 350 parks. The physician can print out a one-page summary of a specific park, detailing what it offers, where it is, and how to get there.

The D.C. Park Prescription Program, focused on children, is a stepped-up version of programs trying to wrest children away from their computer screens and get them out into nature.

It's also part of a broader school of thought linking activity in nature - as opposed to in a gym - with greater physical and mental well-being for people of all ages.

Physicians often tell patients to exercise more. An actual prescription is the next big step, advocates say. It adds oomph and credibility, along with pertinent details.

They're building on the "No Child Left Inside" movement, bringing a new twist to an old adage: "Take two nature walks and call me in the morning."

A few weeks ago, some of the leaders in the field came to Philadelphia to explore the idea of starting a nature prescription program here.

They met at the Schuylkill Center for Environmental Education in Roxborough, where education director Gail Farmer has had a program like this in mind for a while.

"I see it as a game-changer for nature centers and nature and conservation in general," she said. "It's a way to make nature relevant to people who may not automatically think of it as something important in their lives."

Not to mention that it could address chronic health problems - obesity, metabolic disorders, cardiovascular diseases, and more.

The events began with an evening talk by Michael Suk, chief of orthopaedic surgery with the Geisinger Health System. As a White House Fellow, he led the National Park Service's "Park Prescription Program," which now is in many areas - but not the Philadelphia region - and links physicians and patients with parks.

Exercising for better health is nothing new, he said. "What the public-health message fails to address is how and where."

Nature play, he said, advances fitness from an activity you do in a gym - as if it were a chore - to something done outdoors, making it more fun, and something you're more likely to repeat.

The next day, the Schuylkill Center held a several-hour brainstorming session that included members of the American Academy of Pediatrics, Philadelphia's parks and recreation community, the U.S. Play Coalition, the National Park Service, and physicians from Children's Hospital of Philadelphia.

Children's Hospital pediatrician Chris Renjillian said that one of the challenges was "being able to identify a safe place where kids can do stuff with and without supervision."

Others said weather was an issue. Debbie Carr, director of environmental education with the city's Parks and Recreation Department, said busy streets were both a physical and psychological barrier.

Kids are "not used to moving, they're used to their phones," said Sandy McDonnell, director of the pediatric obesity program with the Pennsylvania chapter of the American Academy of Pediatrics.

But more and more cities are starting programs that link nature and health.

In San Francisco, parks are partnering with the American Heart Association. In Boston, Massachusetts General Hospital for Children teamed up with local recreation groups and the Appalachian Mountain Club last year to start Outdoors Rx. Baltimore has a "Docs in the Park" program that holds specific events in parks.

"To the casual observer, it reads as a nice thing that we're doing. But the truth is, what the research is uncovering is this is a necessary thing to be doing," said Michael Weilbacher, executive director of the Schuylkill Center.

"There are benefits to being active, without question," he added. "But there are different benefits to being active in nature."

Leyla McCurdy, a senior director with the nonprofit National Environmental Education Foundation, walked the group through some of the published studies.

Simply spending time outdoors equates to increased physical activity. Researchers who studied children ages 10 to 12 showed that for every hour spent outside, physical activity rose by 27 minutes a week.

Another study of more than 1,500 sixth-grade girls in seven U.S. cities showed that proximity helped. Those who lived within a half-mile of one or more parks had higher levels of moderate to vigorous physical activity in general.

Compared with exercising indoors, exercising in nature has been linked to less tension and stress, coupled with greater intent to repeat the activity, McCurdy said.

Researchers who hooked people up to EEG devices during 25-minute walks saw evidence of lower frustration and higher engagement when moving into a "greener" space.

"What this new research gives us is the bridge between these two different communities," Weilbacher said. "Doctors need parks, and parks need doctors."

For Kimberly Labno, senior program coordinator with the Health Promotion Council, a Philadelphia-based nonprofit that is all about risk reduction and prevention of chronic disease, a Nature Rx program would be one more tool to use.

"We know that behaviors are tough to change," she said.

"I think doctors are hungry for something like this," said Robert Zarr, who heads the D.C. Park Prescription program.

Indeed, other physicians in the Unity system have asked if they can use the database, too. Zarr tells them that they can, although they won't be part of the official study he's conducting to assess how well the program works.

When the young patient comes in 20 pounds heavier instead of 20 pounds lighter, it's clear that "the pills aren't working. The advice isn't working," Zarr said. "This is something new. We've forgotten the importance of going outside" and being active in nature.

Find a Park Near You

While no one site lists all regional parks, here are links to find them.  

The National Park Service allows you to search for national parks by zip code:

The U.S. Fish and Wildlife Service lists national wildlife refuges: www.fws.gov/refuges/

Pennsylvania's 120 state parks and conservation areas are cataloged here:

New Jersey's parks and forests are listed at:

Philadelphia's parks and similar facilities are at: www.phila.gov/parksandrecreation/findafacility/

For other parks, check with counties or municipalities.