Over the years, coffee has been much maligned as an indulgence, a trigger of blood pressure and brown teeth, a diuretic that works against good hydration. Some studies from the 1980s even suggested increased risk for heart attack. Coffee has been classified by many in the "undesirable" list, along with hydrogenated fats and too much alcohol.

But there's another part of the discussion that often gets little attention: coffee's ability to reduce the likelihood of developing diabetes and heart...