Maybe not for heart disease, but stress should be number one for health overall because it affects all the other things you mentioned: sleep, appetite, exercise

Maybe not for heart disease, but stress should be number one for health overall because it affects all the other things you mentioned: sleep, appetite, exercise, and smoking. With the principals being able to work 18h days, I think their discipline plays a huge part, as you wrote, and maybe they're outliers who naturally cope with these demands better than the average person. I personally can't sustain 12h days for more than a month.