MUST SEE: How Obama aged while in office

Is it possible to keep a track of presidency with the increase in number of grey hairs on the President's head? The answer may be in the affirmative.

Since United States President Barack Obama took over the reins of the nation in January 2009, he has shown marks of aging -- a little wrinkling and a lot more grey hair, according to media reports.

According to Cleveland Clinic's Michael Roizen, the burdens of the highest elected office in the US are immense. An average President actually experiences accelerated aging during his term -- eating up two years for every one in the White House.

And clearly, the change in appearance of Obama since his days as a senator till today has left people guessing. Here's a look:

The good young days: In this picture taken in early 2006, a visibly young looking Barack Obama, who was then the senator from Illinois, is seen explaining his 2006 Vote Against Raising the Debt Limit. He was just 45 and the presidency was far away.

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Every reason to smile: No signs of aging yet! Obama listens to speakers at a New Hampshire Democratic Party election celebration in Manchester, New Hampshire in this December 10, 2006 photograph.

This was Obama's first visit to the political proving grounds of New Hampshire, stoking the growing buzz about a possible 2008 White House run by the rising party star.

Shades of grey: Few days after being elected President, and a few grey hairs had sprouted around his temples.

In this December 17, 2008 photograph, Obama is seen interacting with the media, as the president-elect of the United States, during a news conference in Chicago.

(S)tress buster: A year on, the difference is for all to see. Obama had a lot more grey hair as he completed a year in office.

In this, December 27, 2010 photograph taken in Kailua, Hawaii while the US President was on Christmas vacation enjoying a shave ice.

Aging in 'dog years'? This year Obama turned 50! And along with that came the wrinkling of the skin as well as seen in this picture taken on December 6 during Obama's visit to Osawatomie High School in Kansas.

In fact, recently Obama himself admitted that he's aging rapidly in "dog years". "These President years are dog years," Obama had told supporters at a swank fundraiser in Los Angeles this October. "Don't get tired. I may be gray, but I'm not tired. My passion is still there. My vision for this country is still there."

But, here's the silver lining. While earlier research has shown that being President speeds up aging, a recent study revealed that many American commanders in chief have actually lived longer than their peers. Based on the life expectancy data for men the same age as Presidents on their inauguration days, the study found that 23 of 34 presidents who died of natural causes lived several years longer than expected.