Despite reams of research, there's no consensus on whether you'll clearly benefit by drinking a cup or two (or three) of coffee every day. No one disputes that caffeine is a stimulant that jolts the nervous system. That can give you a late-afternoon energy boost but interfere with your sleeping patterns.
Other side effects can vary. Regular coffee drinkers may suffer heartburn, anxiety, irregular heartbeat or dehydration. Because caffeine is a diuretic, your kidneys may cry out for you to urinate more often.
More serious health problems are possible. Coffee can cause blood pressure to spike, although it's unclear whether hypertension can result. And exceeding three cups of decaf per day may contribute to higher levels of LDL cholesterol (i.e., the "bad" one).
While inconclusive, some studies have linked certain cancers (pancreatic and bladder) to heavy coffee intake. An analysis from April 2007 reviewed claims that coffee can raise the risk of stomach cancer or leukemia and called for further study.
Perhaps the most contradictory data relates to coffee and diabetes. It seems that every few months, new research reverses earlier findings about whether coffee plays a small role in helping prevent type 2 diabetes—or increases your risk.
Drink up the good news
There's a growing body of research that indicates the antioxidants in coffee can guard against cancer. Yet the benefit is fairly modest and is more than offset if you don't eat healthy foods.
A series of inconclusive studies have explored whether coffee can help guard against Parkinson's disease, and medical researchers debate this issue hotly. One such study published in 2006 found that among 676 older European men, those who consumed coffee experienced less age-related cognitive decline than non-coffee drinkers. The group with the lowest rates of decline drank three cups a day. Expect more news in the next year.