Interesting question. I'll admit, I'm a bit biased, as I love a strong black coffee. Luckily though, the venerable New England Journal of Medicine has weighed in with an unbiased observational study. (article here. NEJM, May 17, 2012).
Worldwide, coffee is usually NOT considered as a healthy beverage, but still remains one of the most WIDELY consumed drinks in North America, if not the world. We all know about the caffeine in coffee, but coffee also contains many other bioactive compounds, including anti-oxidants and anti-inflammatory compounds that may positively affect health.
This study followed the lifestyle of Americans, aged 50-71, for up to 13 years, monitoring their coffee intake, as well as an overwhelming number of other potentially confounding factors (like TYPE of coffee - ground vs. espresso vs instant) as well as other health indicators like smoking, alcohol, activity level, etc.
The study showed that coffee drinkers tended to be MORE likely to smoke, drink alcohol, and eat red meat than non coffee drinkers! They also tended to be LESS active, have lower education levels, eat less fruits and veggies as compared to those who did NOT drink coffee.
HOWEVER, after controlling for these variables, coffee drinkers were MORE LIKELY to Live LONGER than non coffee drinkers! Interestingly, the benefits remained, whether the coffee was caffeinated, or NON-caffeinated.
There might be some other, as yet, unrecognized reason for this association, and an observational study is not the best way to test an hypothesis, but this study certainly provides some reassurance that morning cup of joe is OK!
BOTTOM LINE: This well done prospective cohort study showed a benefit in drinking coffee with respect to overall mortality, and specifically in heart and stroke mortality, diabetes and infection.
Have a great day, and let me know what you think!!