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There's one place my young daughters love so much that we have to spell out the word in their presence, lest they go berserk: the p-a-r-k. We regularly use a trip to the park as a bribe, and while that may not be the best parenting technique, in this case it comes with incredible rewards.

A new study found that inner-city kids living in neighborhoods with more green space gained about 13% less weight over a two-year period than kids living amid more concrete and fewer trees. Such findings tell a powerful story. The obesity epidemic began in the 1980s, and many people attribute it to increased portion sizes and inactivity, but that can't be everything. Big Macs and TVs have been with us for a long time. "Most experts agree that the changes were related to something in the environment," says social epidemiologist Thomas Glass of the Johns Hopkins Bloomberg School of Public Health. That something could be a shrinking of the green.

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The new research, published in the American Journal of Preventive Medicine, isn't the first to associate greenery with better health, but it does get us closer to identifying what works and why. At its most straightforward, a green neighborhood simply means more places for kids to play — which is vital since time spent outdoors is one of the strongest correlates of children's activity levels. But green space is good for the mind too; research by environmental psychologists has shown that it has cognitive benefits for children with attention-deficit/ hyper activity disorder (ADHD). In one study, simply reading outside in a green setting improved kids' symptoms.

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Exposure to grassy areas has also been linked to less stress and a lower body mass index among adults. And an analysis of 3,000 Tokyo residents associated walkable green spaces with greater longevity among senior citizens. Glass cautions that most studies don't necessarily prove a causal link between greenness and health, but they're nonetheless helping spur action. In September the U.S. House of Representatives approved the delightfully named No Child Left Inside Act to encourage public initiatives aimed at exposing kids to the outdoors.

Finding green space is, of course, not always easy, and you may have to work a bit to get your family a little grass and trees. If you live in a suburb or a city with good parks, take advantage of what's there. Your children in particular will love it — and their bodies and minds will thank you.

—— with reporting by Shahreen Abedin