This is really hard to tease out. Yes, medicine is stressful but so is being a cop or a firefighter or an airline pilot.
Although it is stressful, physicians also have better access to medical care; they are more likely to have a high income compared to the general public and people with higher income, on average, enjoy better health than those of lower income. In addition, they are more likely to have insurance and they are better educated about what they should do to maintain good health than the average Joe. On the other hand, they tend to be more neglectful of their health compared with the general public.
Physicians and nurses and other health professionals (i.e. dentists) have been the subjects of observational research studies and interventions aimed at better understanding chronic diseases including coronary artery disease but the reason for recruiting them has been because they are easy to follow due to their licensure (hard to be lost to follow-up) and they are trusted to be accurate in their reporting of exposures and outcomes when surveyed. (The studies go on to get medical records if someone reports having had a heart attack or other event but accurate reporting by the subject helps facilitate that record retrieval.) Of course, studies of this kind don't tell us if docs are better or worse off, and by how much, than the rest of the populaiton. We also have to be concerned with "health worker bias"; people who are employed in a profession have better health outcomes, on average, than people who are not employed at all.
There is an entire field of study, epidemiology, that examines these sorts of questions.
