High school students whose friends posted photos of drinking and smoking were about 20 percent more likely to become drinkers or smokers themselves. iStockphoto hide caption

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The teenage years are the last golden opportunity to build a healthy brain, researchers say. So smoking pot might not be so smart. Tomas Rodriguez/Corbis hide caption

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Euclid Market, a corner store in East Los Angeles, recently got a makeover to promote healthier eating. It not only sells more fruits and vegetables, but also offers cooking classes and nutrition education. Courtesy of Margaret Molloy/UCLA Fielding School of Public Health hide caption

itoggle caption Courtesy of Margaret Molloy/UCLA Fielding School of Public Health

The CDC would be happy with these guys, who were playing in Birmingham, Ala., in July 2013. Teenage boys say basketball is their favorite activity. Mark Almond/AL.COM /Landov hide caption

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A customer buys produce at the Euclid Market in the Boyle Heights neighborhood of East Los Angeles in December. The market was reopened in 2013 as part of a project to promote healthy eating among the city's Hispanic population. Courtesy of UCLA Fielding School of Public Health hide caption

itoggle caption Courtesy of UCLA Fielding School of Public Health

Janet Wertheimer does a back hyperextension exercise at Boston Sports Club in Wellesley, Mass. Regular exercise has helped control her chronic back pain. Ellen Webber for NPR hide caption

itoggle caption Ellen Webber for NPR

Solid friendships can help buffer life's stress. iStockphoto hide caption

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Colleen Frainey, 16, of Tualatin, Ore., cut back on advanced placement classes in her junior year because the stress was making her physically ill. Toni Greaves for NPR hide caption

itoggle caption Toni Greaves for NPR