When a new President takes the oath of office, he often exudes a youthful optimism. But Presidents tend to leave Washington 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.