...in numerous studies conducted throughout the world, consuming four or five eight-ounce cups of coffee (or about 400 milligrams of caffeine) a day has been associated with reduced death rates.But,
..coffee doesn't warrant a totally clean bill of health...The most common ill effect associated with caffeinated coffee is sleep disturbance...People vary widely in how rapidly they metabolize caffeine, enabling some to sleep soundly after drinking caffeinated coffee at dinner while others have trouble sleeping if they have coffee at lunch. But even if you can fall asleep readily after an evening coffee, it may disrupt your ability to get adequate deep sleep, Mr. Pollan states in his forthcoming book, “This Is Your Mind on Plants.”
Caffeine is one of more than a thousand chemicals in coffee, not all of which are beneficial. Among others with positive effects are polyphenols and antioxidants. Polyphenols can inhibit the growth of cancer cells and lower the risk of Type 2 diabetes; antioxidants, which have anti-inflammatory effects, can counter both heart disease and cancer, the nation’s leading killers.