How fast will Obama age? Two years for every year in office

When a new U.S. president takes the oath of office, he often exudes a youthful optimism. But presidents tend to leave Washington, D.C., visibly wearing the stress of their position.

According to a theory advanced by Michael Roizen, chair of the Wellness Institute at the Cleveland Clinic and co-founder of RealAge.com, presidents age approximately two years for each calendar year in office.

"If they are in office eight years, they typically will age 16 years, twice as many years as they are in office," says Roizen. He analyzed public medical records of previous presidents dating back to Theodore Roosevelt and calculated their biological age based on factors including physical activity, diet, blood pressure and lifestyle habits.

You can clearly see the scars of the office on former President George W. Bush.

"If you look at pictures of him in 2000, he looked almost boyish, and in 2009 when he left office, he looked ravaged," says Robert Gilbert, a Northeastern University political science professor.

Former President Bill Clinton's hair changed from salt-and-pepper when he entered office to powder-white eight years later. And although his health largely held up while in office, he has since undergone heart bypass surgery.

Most American presidents are well educated and have access to top-notch medical care, both factors that are normally associated with a longer life expectancy. But the continuous stress of the oval office seems to have shortened the life expectancy of many past presidents. Of the 32 deceased presidents who were not assassinated, 21 failed to reach the typical life expectancy, according to calculations by Gilbert, author of "The Mortal Presidency: Illness and Anguish in the White House."

The unrelenting pressures presidents experience could contribute to illness of various kinds. Stress may play a role in the development of cardiovascular disease, which was responsible for the death of at least six presidents, including Johnson, Coolidge, Harding, Wilson and both Roosevelts. Unhealthy habits like smoking, lack of exercise and poor eating habits are also contributors.

What's more, the commander-in-chief isn't always able to sneak away and indulge in stress relievers like exercise or the company of close friends. Unlike Supreme Court justices and senators, the president is practically under a magnifying glass every day. And no other person shares the ultimate responsibilities of the office and the legacy leadership leaves behind.

But there are steps the president can take to stay healthy. "The level of stress will increase in a time of crisis, but all presidents that I have been associated with handle stress extremely well," says Lawrence Mohr, who was a White House physician between 1987 and 1993. "It's important that they know how to relax among all of the demands of the job."

Aside from a kicking his smoking habit, Obama, 47, should keep in touch with his old confidants via Blackberry and to have a secret basketball court where he can shoot hoops with a few close friends, Roizen advises.