Heart disease
A number of sound studies have cleared caffeine of a connection with circulatory disease, heart rhythm problems, and sustained high-blood pressure. But temporary increases in blood pressure in athletes who ingest large amounts of caffeine have caused some concern.

Cancer
Extensive studies conducted since a review began in 1978 have failed to find a connection between caffeine and bladder, breast, colorectal, liver, oral, pancreatic, or stomach cancer.

Sleep disorders
There is little question that caffeine in the evening can keep you from getting to sleep. About half of the caffeine you take in is eliminated every three to four hours, so if you avoid caffeine after 6:00 p.m., you should be relaxed by 10:00 or so.

Urination problems
Coffee doesn't appear to cause bladder or prostate problems, but it is a diuretic—that is, it causes your body to eliminate water, sending you to the restroom. If you have a problem with urinary frequency, caffeine will only make it worse. And being dehydrated, which caffeine can contribute to, is not good for you.

If you drink three cups of coffee a day and worry about it, rest easy. At the same time, I don't think there's any strong evidence that you wouldn't be at least as well of without it. Personally, I've cut my coffee from six cups a day to one or two, and I find that my energy levels stay more constant during the day. I still like a cup first thing in the morning, but I'm happy to be off the day-long caffeine roller coaster.