As mentioned by Claire above, the Peace Corps offers some significant benefits. Addtionally, there are also programs allowing an individual to obtain their masters degree (i.e. MPH) while serving in the Peace Corps.
If you'd like to perform patient care however, you'd be better off seeking a practice degree like that of a nurse midwife or nurse practitioner. While the role is not translatable in much of the developed world, there are many places in the developing world that you can practice according to your education. While an MPH is beneficial, once obtaining an advanced practice nurse degree, you may not find it necessary unless you'd like to have more publication clout or if you'd desire to work with the CDC, USAID, or other organization that does more community based health rather than patient care.