“Two cups of coffee a day can reduce the risk of heart failure (but five can be bad for you),” the Daily Mail reported today. This seemingly contradictory headline is actually a fair but slightly overenthusiastic reflection of a review of research that looked at the relationship between regular coffee drinking and risk of heart failure.

Heart failure is a condition  in which the heart cannot pump blood to meet the body’s demands, this can have many causes, the most common being...