A recent study was carried out by the National institutes of Health/American Association of Retired Persons They enrolled more than 400,000 participants from age 51 to over 70 years, and more than 52,000 deaths were accrued from the National Death Index. It included participants from 6 states plus Atlanta and Detroit.
The investigators looked at people who drank no coffee, less than 1 cup, 2-3 cups, 4-5 cups, or more than 6 cups, and then they tallied the rates of deaths in people with heart disease, stroke, diabetes, respiratory disease, cancer, and the other usual conditions you look at.
Then they adjusted for other factors, such as white meat intake, red meat intake, total calories, smoking, and the kind of coffee consumed. When the data were adjusted for those other factors, the clear offender was cigarette smoking and, in fact, the more coffee you drank, it seemed, the lower the risk for all of these other conditions.
Of interest, all of the people who drank more than 6 cups of coffee a day had less college education, ate more red meat and less white meat, ate fewer fruits and vegetables, and had less vitamin supplementation and other supplements -- all the things we think aren't good for us.
Another recent report says that coffee may actually delay or possibly prevent Alzheimer disease. We do not know whether tea would do this, we do not know whether other caffeinated beverages would, or whether it is an effect of caffeine. There are many, many elements in coffee, including antioxidants and other components, that could be responsible for this benefit.