Justin McCowan, 39, has Down syndrome and lives at home with his parents in Santa Monica, Calif. Benjamin B. Morris for NPR hide caption

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Rick and Marianne wash dishes together. She no longer remembers that he is her husband. Andrew Nixon/Capital Public Radio hide caption

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Doctors may eventually be able to diagnose "preclinical" Alzheimer's in patients who have abnormal brain scans but who aren't yet showing behavioral symptoms of the disease. iStockphoto hide caption

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Actor and Alzheimer's advocate Seth Rogen testifies before the Senate Committee on Appropriations about the disease's damaging effects on patients and their loved ones. Mandel Ngan/AFP/Getty Images hide caption

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Vitamin E has been associated with increased risk of death in some studies, but it may also delay cognitive decline in Alzheimer's disease. iStockphoto hide caption

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Researchers have only recently been able to use brain scans to detect Alzheimer's risk factors in living people. iStockphoto hide caption

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An Indian schoolgirl dressed as Telugu Talli poses for the camera during a celebration in Hyderabad, home to a study that seems to show the onset of dementia is delayed for people who speak more than one language. Noah Seelam/AFP/Getty Images hide caption

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University of Florida researcher Jennifer Stamps administers the peanut butter sniff test to a volunteer. Jesse S. Jones/University of Florida hide caption

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Hospital intensive care units save lives, but people there often suffer from delirium. Cal EMA / Flickr hide caption

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Stressed out? Who isn't? Stress can cause physical changes in the brain that may be linked to Alzheimer's. iStockphoto.com hide caption

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