Lowering Resting Heart Rate?

Is there any way to lower my resting heart rate, it's currently at 78 bpm... I have been working out for the past 7 months, both strength, endurance, speed, stamina, agility workout - but my resting heart rate has not gone down... I have pushed myself to the max, actually have reached my maximum heart rate and one time even exceeded my maximum heart rate (what should be) I don't know how (10 km straight run, 2 hours of straight workout, and than 1 hour of abdominal workout, and another hour of punching a punching bag as well as kicking)... now, this has not lowered my resting heart rate at all.. any advice?

ONE MORE QUESTION:

Ever since I have started working out, I have been eating 2x more than my original diet, so I usually end up consuming a lot more sodium than I am supposed to have... is this okay or bad for my health? Also, is it normal to be eating 2x more than your original diet? I am just guessing it's because your body needs more nutrition?