President Obama turns 50 today. He's a little grayer than he used to be - like many other presidents before him.
But do presidents actually age more quickly than the average American?
Dr. Michael Roizen, chief wellness officer of Cleveland Clinic and founder of RealAge.com, has studied presidents going back to 1901. He says presidents age two times faster while in office, primarily -- but not only -- due to stress.
Click on the video below for more on why Roizen says presidents age more quickly -- and why it's not all about the pressure of the job.