I'm usually sceptical of medical studies and you sometimes find that something touted as beneficial is later found by another study to be not so good ... or vice versa (eg fat). As caffeine is a stimulant it may not be good for some people with a heart condition. What may work for some doesn't necessarily work for all and seeking qualified advice is always advised if you have a medical condition (don't depend on Dr Google).
Moderation is also advisable but what is considered a moderate amount may vary. Some people can drink 6+ cups a day without any problems. Three is my limit and I usually drink 2 a day.