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It鈥檚 more than just a few flecks. President Barack Obama, who turned 50 in August, is definitely going gray. He鈥檚 said the color change runs in and has mentioned a grandfather who turned gray at 29.

But others see it as a sign that the presidency is taking a toll on Obama, as it has other on presidents. Dr. Michael Roizen, of RealAge.com fame, says when they鈥檙e in office. The main cause, he says, is 鈥渦nrequited stress鈥攖hey don鈥檛 have enough friends to mitigate the stress,鈥� which brings to mind the line commonly attributed to Harry Truman:聽.

Accelerated presidential aging? Not so.

The only problem with this notion of accelerated presidential aging is that it just ain鈥檛 so, according to , a professor at theUniversity ofIllinois at Chicago and a longevity expert.

In an article in tomorrow鈥檚 (JAMA), Olshansky says his research into presidential life expectancy found no evidence that American presidents die sooner than other American men of their time. In fact, quite the opposite: most of them lived long lives and beat the longevity expectations for their time.

Olshansky limited his analysis to the presidents who died of natural causes, excluding the four who were assassinated (Lincoln, Garfield, McKinley, and Kennedy) and the five who are still living (Carter, the two Bushes, Clinton, Obama). That leaves 34. By his calculations, 23 of them exceeded the life expectancy of men the same age as the presidents when they were elected, even if you built in the (apparently false) assumption that the presidents experienced a doubling of biological aging while they鈥檙e in office.

John Adams (life span, 90.7 years), Herbert Hoover (90.2), Gerald Ford (93.5) and Ronald Reagan (93.3) exceeded the average life expectancy by the largest margins. Seven of the first eight presidents lived to a ripe old age: their life spans averaged 81.5 years. 鈥淭hey lived as long as American women do today,鈥� Olshansky noted. The exception was Washington, who died at age 67.8.

James K. Polk (53.6), Chester A. Arthur (57.1), and Warren G. Harding (57.8) were the furthest below expectations.

Privileged people, including presidents, live longer

In his JAMA article, Olshansky offered a couple of explanations for presidential longevity.

All but 10 of the deceased presidents were college educated, wealthy, and had access to the top medical care of their day. The correlation between high socioeconomic status and long life is strong and consistent.

The other explanation is that these men were survivors. To reach the age at which they became president (the average was 55.1 years), they had to get through the perils of birth, early childhood, and young adulthood. Especially in the 18^th, 19^th, and early 20^th centuries, that wasn鈥檛 easy, so these men probably had some inborn hardiness, as well as fortunate circumstances.

Do our eyes deceive us? Yes they do.

And yet presidents do seem to age before our eyes. Olshansky says that鈥檚 partly because we just notice it more in someone who lives in the public eye.

In his JAMA article, Olshansky cited a study that connected gray hair to stress. But in his conversation with me, he emphasized that the outward signs of what we commonly attribute to aging and genuine aging aren鈥檛 necessarily related. 鈥淕etting wrinkles and turning gray鈥攖hey really don鈥檛 matter very much,鈥� he said.

I just looked in the mirror and couldn鈥檛 agree more.