For many years there were reports that coffee caused pancreatic cancer and other maladies. But studies have proved coffee is not bad for you. In fact in 2010 or 2011 Harvard's Walter Willet said extensive studies have shown, "It's turned out to be remarkably safe. The evidence is very clear that coffee doesn't increase the risk of pancreatic cancer, and it probably reduces the risk of liver cancer." A 2007 Swedish study estimated that people who drank two cups of coffee a day had about a 30% lower risk of liver cancer than those who drank none. These tests did not include decaffinated coffee so no results on that.
Harvard's Willet also stated, "Coffee almost for sure reduces the risk of type 2 diabetes. When researchers combined nine studies on a total of nearly 200,000 people, they found that those who drank four to six cups of regular or decaffeinated coffee a day had about a 30% lower risk of diabetes than those who drank up to two cups a day. It looks like coffee reduces insulin resistance."
Those who drank either decaf or regular coffee also appeared to have less gout and heart disease. However, Willet also said, "Only caffeinated coffee may lower the risk of Parkinson's disease and gallstones. The mechanism is not clear, but the evidence is quite strong for Parkinson's."
Willett went on to say that bottom line, "Coffee has turned out to be a health-promoting beverage rather than a carcinogen."