With today being Inauguration Day, I would like to take a few moments to reflect on the physical and psychological aging that goes on when you are in a high-stress job with tremendous responsibility. It isn't just being President of the United States, though of course the health of our president is everyone's concern.

Back in 2004, I interviewed former President Clinton's heart surgeon, Dr. Craig Smith, for the Washington Post, and I was amazed at how clogged Clinton's arteries were prior to his extensive heart bypass operation. Of course, Clinton was a famous fast-food junkie, and he also admitted later that he wasn't completely compliant with his cholesterol-lowering medication. Clinton exercised, played golf, and kept his weight down, but his photographs show him visibly aging over his 8 years in office.

George W. Bush is a runner, and exercised vigorously throughout his 8 years in the White House. During most of his first term, Bush reportedly ran an average of three miles, four times a week, also swimming, lifting weights, and working on an elliptical trainer. But reportedly damaging the meniscus of both knees, Bush switched to mountain biking for his regular exercise during his second term. Bush's regular exercise throughout his presidency, and more careful diet than Clinton's, will make it far less likely that he will suffer from heart problems in the future. Another factor is genetics - the good health of Bush 41 (who once again plans to jump out of a plan for his 85th birthday), as well as that of Barbara Bush, is a good indication that Bush 43 will also remain in good health. Still, looking at photographs of President Bush over the past 3 years reveals a man aging visibly under the stress of the job.

Barack Obama is 47 years old, thin, and also exercises regularly and vigorously. He is a lover of basketball, and reportedly plans to play in the White House gym. The greatest concern for his health, if he manages to avoid the cream sauces and desserts of State dinners, will be smoking. We don't know how much Obama has smoked over the years, and he has promised not to smoke in the White House, but stress and cigarettes are a dangerous combination. Here's hoping that our 44th president can kick the habit for good. If he does, then his long-term risk of heart disease, lung disease, and cancer will decrease dramatically.

Dr. Marc Siegel is an internist and associate professor of medicine at the NYU School of Medicine. He is a FOX News medical contributor and writes a health column for LA Times, where he examines TV and movies for medical accuracy. Dr. Siegel is the author of "False Alarm: The Truth about the Epidemic of Fear"and "Bird Flu: Everything You Need to Know About the Next Pandemic." Read more at www.doctorsiegel.com

Dr. Marc Siegel, a practicing internist, joined FOX News Channel (FNC) as a contributor in 2008..