President Barack Obama's 49th Birthday

President Obama Grudgingly Celebrates His 49th Birthday.

President Obama turns 49 years old today, and while it's not quite the milestone of the big 5-0, clearly he is ringing in another year only grudgingly.

Obama has made references in the past week to the outward signs of his aging.

"I will be 49 this week," Obama said in Atlanta on Monday. "I have a lot more gray hair than I did last year."

He followed that comment this week with two more references lamenting his dark hair going grayer with each month in office.

White House press secretary Robert Gibbs said the job as commander-in-chief is one the president no doubt enjoys, but it will just require him to get more frequent haircuts to cover up those pesky gray hairs.

"I can't imagine that the weight of the job doesn't take a toll physically and mentally on anybody that does it," Gibbs said at the White House daily briefing Tuesday. "But at the same time ... I would say he's still in pretty good shape and is enjoying the job even with its many challenges. ... There's no doubt that it takes an enormous physical and mental strain on making the decisions that you make."

And then there are the inward signs of his age -- a slowing metabolism.

At the Tastee Sub Shop in Edison, N.J., last week, the president implied that his upcoming birthday means that he has to start making smarter choices about his food portions.

"I want everyone to know [that] when I was 20 I could order a 12-inch," he joked. "I'm turning 49 next week, which means [I can order] just the half."

Dr. Michael Roizen of the Wellness Institute at the Cleveland Clinic and co-founder of RealAge.com, said a president typically ages two years for every one year in office.

"The number one ager for all of us is stress," Roizen said, adding that and lack of socialization really wear on presidents.

"It's a very high-stress job, but they lose their friends," Roizen said. "Typically, when they come into office they have friends. But by the time they leave, most of those friends apparently are asking for something. So they lose their confidants."