Myth: Drinking coffee causes dehydration.

Facts: Not so, recent research shows. “The evidence does not support the belief that caffeinated beverages, including coffee, cause dehydration,” says Alice Lichtenstein, director of the Cardiovascular Nutrition Lab at the Jean Mayer Human Nutrition Research Center on Aging at Tufts University in Boston.

The reason for this belief is that many people think their morning joe acts as a potent diuretic. Actually, when you down a cup of coffee, you don’t excrete any more fluid than you would from drinking one cup of water, says Christine Gerbstadt, M.D., a media spokesperson for the American Dietetic Association.