Presidents of the United States, it seems, age right before our eyes.
Their faces, creased and drawn, are road maps of wars and natural disasters and economic calamity. Tufts of gray hair bear testament to a job framed by unremitting pressure and unrelenting criticism.
A vibrant Jimmy Carter beamed with optimism when he assumed the post in January 1977. As he departed four years later, he was wan and pinched, the legacy of hostages in Iran and energy shortages at home - a cautionary tale for President-elect Barack Obama.
But is accelerated aging in the Oval Office inevitable?
Almost certainly, say some specialists in aging and politics. The pounding stress of the job can unleash biological forces that translate into wrinkles, gray hair, weight fluctuation - and sometimes even premature death, although there is far from universal agreement on the long-term health effects of the presidency.
Dr. Michael Roizen, who has written extensively on aging, said a formula he helped develop suggests that for every year in office, the average president ages two years.
"It doesn't matter if they're Democrats or Republicans, it doesn't matter if they've been athletes or not beforehand, it doesn't matter if they were smokers or not," said Roizen, chief wellness officer at the Cleveland Clinic. "For eight years in office, they age 16 years."
Roizen's analysis, which examines presidents from Theodore Roosevelt forward, relies on medical documents presidents made available before being elected and details from annual checkups while in office. It includes medical factors such as blood pressure and weight and behaviors such as smoking and exercise.
Using his widely publicized "Real Age" formula, Roizen then calculated each president's risk of death and disability before he was elected and after his term had ended. The results showed a consistent acceleration of aging among presidents, said Roizen, who has sometimes faced criticism from peers for his outspoken views on human aging.
Others measure the health toll of the presidency not in gray hairs and wrinkles, but in life expectancy. In his book "The Mortal Presidency," Northeastern University political scientist Robert E. Gilbert reports that presidents, on average, have shorter life spans than members of Congress or the Supreme Court.
And when he examined the ages at which presidents from Washington to Nixon died, Gilbert concluded that 25 of 36 died earlier than would have been predicted using the sort of life expectancy data that insurance companies rely on.
To reach his findings, Gilbert did not look simply at life expectancy from birth. Instead, he mined actuarial life tables to compute how much longer a man of a given generation could be expected to live assuming he made it to certain milestone ages.
Consider Theodore Roosevelt. It was expected that his contemporaries - men born in the late 1850s - would live to be almost 75 if they had survived childhood scourges and war to make it to at least 60. Roosevelt saw his 60th birthday, but no more. So Gilbert concluded Roosevelt died nearly 15 years prematurely. Woodrow Wilson, he calculated, lived roughly seven years less than actuarial tables would have forecast for someone of his generation.
"To be president, you have a position where you are really the focal point of attention," Gilbert said. "Whereas with a Supreme Court justice, you're one of nine. And if you're a member of Congress, you're one of 535. When justices go to their homes, the reporters don't bother them. If they go to the beach, who would even know them?"
Not all doctors agree that presidents are doomed to an early grave. Just look at the longevity of our most recent batch of past presidents, one specialist said; Carter, especially, continues to hopscotch the world deep into his 80s. Herbert Hoover, Harry Truman, Gerald Ford, and Ronald Reagan substantially outlived their contemporaries.
"It's true that when people have the weight of the world on their shoulders, they may get more wrinkles," said Dr. Leo Cooney, chief of geriatrics at Yale School of Medicine. "But the data that this impacts their health is not there."
History is pocked with nonpresidential examples of intense stress fueling aging and early death - among humans and animals, including gorillas.
Dr. Ken Minaker, chief of the Geriatric Medicine Unit at Massachusetts General Hospital, cited the fate of some who survived Nazi occupation during World War II and, after years of privation and fear, experienced higher rates of Alzheimer's disease and premature death.
When humans endure levels of pitched stress, a dangerous cascade of hormones - such as cortisol - begins flowing.
And while younger people can easily reset their hormonal response system once acute stress subsides, older adults don't respond with the same suppleness. In such circumstances, the human body becomes like an engine that is constantly revving.
"It's a good thing that older people can have stress responses, but it's a bad thing that your stress responses stay active for a longer period of time," Minaker said. "It's sort of burning you up."
And all that stress, Minaker said, consumes plenty of fuel, which can cause nutrition and even blood flow to be redirected from relatively unimportant tasks such as producing new hair. As a result, longer-lasting gray hairs proliferate.
Rampaging stress hormones also cause more sugar to spill into the bloodstream, which, in turn, damages blood vessels, paving the way for heart attacks and strokes, said Dr. Michele Bellantoni, a geriatrics specialist at Johns Hopkins University.
"I've seen the stories where you show a photograph of the president at Inauguration Day and then a picture later on, and you see aging and you say, 'Was that person under a sun lamp every day?' " Bellantoni said.
"Well, no. They were under stress."
Dr. Burton Lee witnessed the rigors of the presidency from inside the White House. He served as physician to George H.W. Bush during his entire term in office.
"You can watch presidents age in office," Lee said in a phone interview.
Bush's health, he said, was robust until he was diagnosed with a thyroid condition called Graves' disease. When he recommended at one point that Bush take a vacation, Lee said, he was ridiculed. But, aging specialists said, that's exactly what presidents sometimes need, along with enough sleep and exercise.
The Cleveland Clinic's Roizen said that his analysis of presidential aging - as well as insights he gained in conversations with several former presidents - shows the biggest liability was a lack of real friends. Presidents, he said, tend to become isolated, wary of even their closest advisers.
"It takes about six close friends or social groups where you can let your hair down for you to be able to relieve the stress you have," Roizen said.
The next occupant of the Oval Office has pledged to foreswear one particularly dangerous vice: smoking. And in an interview with the magazine Men's Health, Obama indicated that he plans to stay fit. The small outdoor basketball court at the White House "may need an upgrade," he said.
Still, with two wars and a flagging economy awaiting, there's no guarantee that a commitment to exercise will be enough to keep wrinkles from burrowing or gray hairs from sprouting.
"You take a look at someone going into office and then look at someone coming out of office, and they all look beat up," said Dr. David Reuben, chief of geriatrics at the David Geffen School of Medicine at the University of California at Los Angeles. "It is as stressful as it gets."
Stephen Smith can be reached at email@example.com.