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Vitamin E

Once upon a time, researchers thought this antioxidant could protect the heart, but a large trial published in 2005 found that 600 international units (IUs) every other day neither prevented cancer nor lowered the risk of heart attack or stroke in middle-aged and older women. (More recently, a 2008 study found no benefit of 400 IUs every other day in middle-aged and older men.)

Bottom line: Forget the supplements and get your vitamin E from food (oils like safflower, peanuts, eggs, fortified cereals, fruits, and green, leafy vegetables). Bear in mind that cooking and storing foods with vitamin E can reduce the amount you're getting.