It's an appealing notion that our daily pick-me-up may also confer a range of health benefits. And for coffee drinkers there's a lot of research percolating. Several studies suggest that a daily caffeine habit may help protect against Alzheimer's disease. But there's a catch. The cup or two a day that most Americans drink doesn't seem to be enough. Researchers say 500 mg of caffeine, or about five cups of regular coffee, is the dose that seems to protect the brain.