Data from the Twins Early Development Study shows areas in the U.K. where the effect of environmental factors, shown in pink, trumps the influence of genes, shown in blue, and vice versa. TEDS hide caption

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A woman pours two tablets into her hand from a pill bottle. iStockphoto.com hide caption

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Panel Questions Benefits Of Vitamin D Supplements

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A Pakistani man wheels Jamshid, an 8-year-old girl with polio, around the outskirts of the capital Islamabad last July. Behrouz Mehri/AFP/Getty Images hide caption

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Gilead Sciences' Truvada is a step closer to being approved as a way to prevent HIV infection. Paul Sakuma/AP hide caption

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Nurse Susan Peel gives a whooping cough vaccination to a high school student in Sacramento, Calif. The whooping cough vaccine given to babies and toddlers loses much of its effectiveness by the time people reach their teens and early adulthood. Rich Pedroncelli/AP hide caption

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Feds Join Fight Against Whooping Cough In Washington

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An electron micrograph of human norovirus. Charles D. Humphrey/CDC Public Health Image Library ID 10708 hide caption

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Bartender Matt Carucci says he rarely feels safe biking in the city but often rides without a helmet anyway. "There are a lot of other ways to hurt yourself," he says. John Rose/NPR hide caption

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Noah Stewart shelters in the closet just 15 minutes before an April 2011 tornado demolished his house. Wearing the helmet may have saved his life, one doctor says. Courtesy of the Stewart family hide caption

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Kristen Miller talks over the risks and benefits of colonoscopy with Stephen Hanauer, chief of gastroenterology at the University of Chicago Medical Center. Brian Kersey/AP hide caption

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Doctors, don't order that CT scan when a less-expensive ultrasound would work just as well, the Choosing Wisely campaign advises. Catherine Yeulet/iStockphoto.com hide caption

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Doctors Urge Their Colleagues To Quit Doing Worthless Tests

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A package of K2, a concoction of dried herbs sprayed with chemicals sometimes called synthetic marijuana. New York moved to ban a wide range of products like these this week. Kelley McCall/AP hide caption

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