by Patrick Appel
A reason why research on the subject has been mixed:
Heavy coffee drinkers in the study were more likely to be smokers – which makes sense, since the data was collected beginning more than 40 years ago. [Rob van Dam, an epidemiologist at the Harvard School of Public Health] thinks the research didn’t do enough to control for smoking. In fact, as we’ve previously reported, lots of studies in the 1980s failed to control for the link between coffee drinking and smoking, which is one big reason why early research appeared to give coffee a bad rep. Evidence suggesting health benefits from coffee began to emerge only as studies separated the two habits.
The Dish 