Coffee is a healthful beverage that studies have shown can prevent strokes and even help you live longer. But a new study from the Mayo Clinic shows that, with coffee, you can definitely get too much of a good thing. The bottom line: Cap your consumption at three cups a day.

By looking over the Aerobics Center Longitudinal Study, which tracked the lifestyle habits of nearly 45,000 people, ages 20 to 87, from 1979 until 1998, and deaths by all causes until 2003, researchers found that those 55 years and under who consumed more than 28 cups of coffee a week were twice as likely to die compared to non-drinkers.

But don't put down the mug just yet, says Carl J. Lavie, one of the study authors. Four cups per day seemed to be a tipping point; there was no increased mortality with doses of less than 28 cups per week. "High coffee consumption could just be associated with increased death risk," he says. "We were able to control for smoking and fitness, but not for sleep deprivation, stressed-out life, and other factors that could play a part." And don't forget the evidence that regular consumption of coffee can delay onset of type 2 diabetes, cardiovascular disease, Parkinson's, Alzheimer's, and some forms of cancer.

"I personally feel one to two, probably even two to three, cups of coffee per day are safe," says Lavie. "If you drink more than that, it's probably a good idea to try to cut back."