How does your child's spoonful of medicine measure up? hide caption

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A man sunbathes in Malmo, Sweden, in July. Humans (and other animals) make vitamin D when exposed to sunlight. Johan Nilsson/AFP via Getty Images hide caption

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A CT scan of the brain shows the cerebellum, a small portion of each temporal lobe, and the sinuses. Andrew Ciscel via Wikimedia Commons hide caption

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Megan Lindsey (right) and her friend Alexandria Bodfish at soccer camp at University of Notre Dame.  Megan, 14, suffered concussions twice this fall while playing soccer. Courtesy of Barbara Wirtz hide caption

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Cycling has at least tripled over the past two decades in several big cities across the U.S., including Minneapolis, Chicago and San Francisco. Jonathan Steinberg hide caption

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