Since I kicked caffeine (about 3 years ago), my resting heart rate has gone down, my hands are rock steady, I sleep better, and I know longer get crippling head

Since I kicked caffeine (about 3 years ago), my resting heart rate has gone down, my hands are rock steady, I sleep better, and I know longer get crippling headaches when I forget my caffeine fix. How much caffeine did the people mentioned in this study regularly consume? When I was addicted to caffeine, the stimulant effects were no longer helpful, because I was resistent to it.