Reviewing the evidence, a cautionary tale develops about how difficult it can be to construct a good study and interpret the results. Readers also need to remember that the information provided depends in part on who is delivering it, who is paying for it and what they want you to hear. Here are a few points to keep in mind:

• A study of caffeine is not the same as a study of coffee. This is a common problem with dietary studies: in an attempt to make the study more accurate, researchers might decide to isolate a single component from a food or beverage. The food itself, after all, will have variable quantities of that component. However, there can be very different results when consuming the whole food vs. an extracted part.

• A “cup” of coffee is typically assumed to be 6 oz. – not your 16 oz. travel mug!

• Caffeine levels are usually assumed to be about 100 mg per cup, but in fact vary significantly with the type of bean, brewing method, and even from batch to batch. Brewed coffee is estimated to range from 100-150 mg per cup, a similar volume of espresso having about 90 mg. Arabica beans have less caffeine than robusta beans.

Two health topics are commonly associated with coffee consumption – its effect on blood sugar and insulin resistance, and its effect on the adrenal glands. But there has also been considerable research on the consumption of coffee and the incidence of cancer.