In all three studies, the odds of developing heart failure declined for participants who drank at least a cup of caffeinated coffee a day, but how much the risk fell varied. For instance, two of the studies found a decrease in risk of 5 percent to 12 percent per cup consumed daily, compared with no coffee consumption. The other study found no drop in risk for one cup a day but a 30 percent reduction in risk for two or more cups a day. In the report, published in an American Heart Association journal called Circulation: Heart Failure, the researchers described caffeine as “an important contributor” to the heart failure risk reduction linked to coffee. They found that drinking decaffeinated coffee did not have the same effect. Overall, increased caffeine consumption “irrespective of source” was linked to a drop in heart failure risk in all three studies. But the researchers and other experts stop short of recommending that people increase their caffeinated coffee consumption. Caffeine, which is a stimulant, can make you feel more alert and less tired, but, especially in large doses, it also can boost blood pressure and heart rate, make you jittery and contribute to insomnia.