Barack Obama not the only president to go grey in the White House

Worry lines. More pronounced age spots. Flecks of grey dusting his scalp.

As Barack Obamaprepares to deliver his final state of the union speech tomorrow night,eight years after campaigning on the promise of"Change wecan believe in," his physical appearance bears changes you can clearly see.

"You can see it in the greying of the hair, you can see it in the wrinkling of the skin," says S. Jay Olshansky, a board member of the American Federation for Aging Research. "That may well be accelerated because of the stress associated with being president."

Two terms holding America'shighest office can do that to a man. Doctors and aging specialists have long said that the rigours of the Oval Office can transform a spry president-elect into a craggy elder statesman in what seems like no time.

Dr. Michael Roizen, a preventative medicine specialist at the Cleveland Clinic, analyzed presidential medical records from the 1920s onwards and estimated that sitting presidents age two years for every one year spent as what's sometimes called the leader of the free world.

John Hay, Abraham Lincoln's private secretary, once wrote that Lincoln "aged with great rapidity" by his second inauguration in 1865, noting that "the eye grew veiled by constant mediation on momentous subjects; the air of reserve and detachment from his surroundings increased."

Franklin D. Roosevelt assumed the nation's top post in 1933, but by 1945, his declining health, due to polio, was visible from his appearance. Liver spots emerged and the circles under his eyes darkened from fatigue.

During Lyndon B. Johnson's six years as president, from 1963-1969, his hairline thinned noticeably and he formed deeper folds around his cheeks and forehead.

Richard Nixon's sunken eyes sagged deeper and his natural scowl drooped further by the time he resigned the office in 1974 after serving five years.

The 'White House effect'

This so-calledWhite House effect has apparently not spared Obama, who still had a head of youthful black hair back in January 2009when he was sworn in. On his 50th birthday in 2011 in Chicago, observers noted a crown of salt-and-pepper creeping in, as well as deeper creases around his mouth.

Obama himself couldn't resist pointing out the grey hairs that he has been sprouting in more profusion of late.

"I look so old, John Boehner's already invited Netanyahu to speak at my funeral," he joked during the 2015 White House Correspondents' Association dinner.

But if sitting presidents appear to be aging before our very eyes, that's because they are, saysOlshansky, a human longevity expert with the School of Public Health at the University of Illinois at Chicago.

"Most presidents become president sometime between their early 40s and late 60s," he says. "If you take lots of photographs of just about anybody in that age range, you'll notice the usual aging in all human bodies. Greying of hair, loss of hair, wrinkling of skin."

Perhaps nobody in public life is in the spotlight more, or as photographed as often as the president of the United States.

But ifpresidents experience double-time aging while in office, then Harry S. Truman should have died at 68.1 years old.

• Jimmy Carter's latest brain scan good news, doctors say
• Jimmy Carter says latest brain scan shows no cancer
• Obama turns 2016 hopefuls into comic fodder for media dinner

Instead, Truman lived until he was 88.6, after serving two terms and dealing with the pressures of deciding whether to drop the atom bomb on Japan during the Second World War.

Although Olshansky says that while stress can exacerbate the outward appearance of aging, "you don't die from grey hair and wrinkling skin."

Actually live longer

In a 2011 article in the Journal of the American Medical Association, Olshansky examined the lifespans of presidents who died of natural causes, anddetermined that presidents tended to live longer than the mean estimated lifespan for U.S. adult males in the same eras.

"That's not unexpected, of course," Olshansky adds. "Presidents are generally almost without exception all wealthy, almost all highly educated, and have access to the best medical care in the world."

Some presidents might even thrive from their high-pressure job.

"The classic example would be president Clinton, who seems to really thrive when he's in the limelight, and that's not inconsistent with what you see in many presidents," Olshansky said.

Clinton was 43 when he took office in 1993 with a distinguished grey coif. Heleft the White House in 2001 at the age of 51 with an almost completely polar white mane.

Dr. Connie Mariano saw him aging firsthand during some of the nine years she spent as the White House physician from 1992-2001, whenClinton was her patient.

"When Bill Clinton came in at the end of the year, he wasn't doing as much jogging. At the end of his presidency, he was all grey," Mariano said.

"But I also have pictures of Bill Clinton and myself at his start as president, and eight years later, we both looked older, the two of us."

The former director of the White House Medical Unit says being president likely didn't help Clinton's heart disease, and he underwent emergency quadruple-bypass surgery in 2004.

But Mariano believes the presidency attracts a special kind of personality, one who is equipped to deal with life's stresses. Aside from Clinton, she counts among her "favourite patients" former presidents George H.W. Bushand George W. Bush.

"They're sort of experts on how they handle stress. They're tough, and they have a great ability to compartmentalize," she says. "I'd see Bill Clinton on the golf course and he'd be able to focus on just that,and not let the problems of the world interfere with his enjoyment of the game."

Even if presidents handle stress better than average populations, a Harvard study from late December suggests that election winners tended to die sooner than the opponents they defeated.

AnupamJena, an associate professor atHarvard Medical School, looked at about 250 elected world leaders and250 runners-up in 17 different countries in order to compare candidates with similar socio-economic standings andeducation levels.

Without being able to study a president's identical twin as a control, "the next best alternative to a Barack Obama is to compare someone like a Mitt Romney," he reasoned.

Jena's group concluded that even though politicians live longer than the overall population, heads of state tended to live an average 2.5 years less than therunner-up candidates.

"Two and a half years is a pretty long time, and I would speculate that this mortality cost is associated with the stresses of governing a nation," Jena says.

Even so, the right lifestyle choices canprolong one'slifespan. Clinton became avegan and started monitoring his blood pressure, for example.

"And I understand the Canadian prime minister is a boxer," Jena said. "So he's probably in pretty good shape."