Story highlights Wealth, access to healthcare, and education are all closely linked to longer lifespans

Researcher collected the birth, death, and inauguration dates of every American president

Two-thirds of presidents lived (or are living) longer than their projected lifespans

Earlier this year, sociologist Jay Olshansky, Ph.D., watched President Barack Obama return to his hometown of Chicago to celebrate his 50th birthday. In the days that followed, Olshansky was struck by the amount of media coverage dedicated to a single question: When did Obama's hair get so gray?

Being president is a demanding job -- especially in times like this -- and it seems plausible that the stress of juggling politics, the economy, and the military could literally take years off a person's life.

Michael Roizen, M.D., a doctor at the Cleveland Clinic, in Ohio, even suggested on Obama's birthday that presidents age twice as fast as normal while in office.

But Olshansky, a professor of public health at the University of Illinois-Chicago, wasn't buying it. Wealth, access to healthcare, and education are all closely linked to longer lifespans, and presidents have all three resources in abundance, he reasoned; if anything, presidents should age slower than the average person.

To test his hunch, Olshansky collected the birth, death, and inauguration dates of every American president that died of natural causes. (He also included living presidents.) Then, based on their time in office, he estimated their projected lifespans under Dr. Roizen's "accelerated aging" theory.

Two-thirds of presidents lived (or are living) longer than their projected lifespans, Olshansky found. What's more, two-thirds also made it past the average lifespan of men in their age group.

"The first eight presidents lived an average of 79.8 years during a time when life expectancy for men was under 40," says Olshansky, whose findings were published today in the Journal of the American Medical Association. "It seems like most presidents live exceptionally long lives."

If that's the case, what explains the rapidly graying hair and premature wrinkles that seem to beset presidents? (Obama isn't the only president whose visible aging has attracted attention: In years past, the media hasn't failed to note that Bill Clinton was white-haired by the time he left office, that Jimmy Carter had baggier eyes, and that George W. Bush developed new lines across his forehead.)

The obvious answer is that U.S. presidents are simply older when they leave the White House as when they enter. They also take office in their mid-50s, on average -- a stage in life when the external signs of aging tend to become more pronounced in men.

In addition, Olshansky suspects, high levels of stress may indeed contribute to superficial aging, even if they don't shorten lifespan.

"There is good, strong literature to suggest that stress can lead to accelerated graying of hair," he says. "There's no question that stress has a powerful effect, but at least with regard to the presidents, it doesn't appear to be making them die sooner."

Olshanksy plans to study people in other high-stress jobs -- like CEOs of insurance companies -- to test whether stress really does influence how old they look.

Either way, he says, Obama and other stressed-out workers shouldn't fret over their appearance. "No one dies from gray hair and wrinkles," he says.