My wife has a MPH. The great thing about a MPH is that you can work in almost any field you may be interested in. You can do various aspects, such as epidemiology, health education, policy, etc...and in any area of health (infectious disease, chronic disease, environmental health, etc.) Public health typically focuses on prevention and controlling the course disease in the population. My wife constantly complains about working with physicians who do not understand the value of public health and that the 2 fields should be working together...which often does not happen. I think that having a MPH along with a MD will only make your career as a physician even more beneficial for the betterment of your career and for your patients.