从豪宅到专机，享受诸多特权的美国总统们，也有着比常人更多的压力和烦恼。按常理，他们应该衰老的更快。但是美国一项研究表明，总统们老得快但寿命长。美国伊利诺伊大学研究者奥利尚斯基主攻人类衰老学科，他有一套寿命预期模型。这一模型计入各种因素，包括生存环境、饮食、压力、医疗状况等，可预期或计算某一时期特定年龄人群的寿命，也可针对某一特定个体定制，单独预期寿命。奥利尚斯基以美国历史上的所有总统为研究对象。结果发现，自然死亡的34位美国总统平均年龄73岁，比模型预期的68岁长5年。其中，实际死亡年龄超过68岁的总统总计11人，平均寿命78岁。奥利尚斯基说，历任总统时常面对高强度压力，衰老速度肯定比同龄人要快。但他们受教育水平、特别是他们担任总统后所获得的医疗服务一般都高于同龄人平均水平，因此，总统衰老快但是寿命更长。

Obama's estimated life span is 79.3 years, according to Olshansky, but he adds that Obama will probably live longer than that because of his education, wealth and health care.

The American presidency comes with perks, from a very nice house to a handy jet at your disposal, but the job also comes with plenty of stress.

Enough stress to take years off your life? Maybe not, new research suggests.

The data showed that presidents who die of natural causes don't seem to lose years off their lives due to the effects of time spent in the White House. In fact, most of them managed to live longer than similar men of their era.

The findings don't prove definitively that stress of the presidency has no effect on the life span of presidents. It may still take years off their lives; the research doesn't compare them to men of similar wealth and position, such as members of Congress.

Still, "they did a lot better than one would have predicted, given the circumstances that they were in," said study author S. Jay Olshansky, a professor of public health at the University of Illinois at Chicago. "There's no evidence that they're dying earlier."

Olshansky also thinks he's shot down one assumption: that each year in the White House typically takes two years off a president's life. A recent news report about that assumption, prompted by photos that showed the aging of President Obama, led Olshansky to try and see if there was any truth to it.

He was skeptical because presidents share three traits that have been linked to longer life spans: wealth, education and access to health care. "They've scored the trifecta," he said.

Olshansky compared the life spans of presidents who died of natural causes to the life spans of men who were of the same age as the presidents when they were inaugurated. There was a hitch, however, because full American statistics from 1789-1899 weren't available; Olshansky compared presidential life spans in that era to statistics from France, where he thinks men would have lived about as long as in the United States.

Of the 34 who died of natural causes (all except Kennedy, McKinley, Lincoln and Garfield), 23 lived longer than the average man would have, based on their ages at inauguration. They would have lived longer than the average for other men of their era even if they'd somehow aged at twice the normal rate while serving as president.

Commenting on the report, Dr James Goodwin, director of the Sealy Center on Aging at the University of Texas Medical Branch, said the idea that presidents will be adversely affected by stress is "fundamentally flawed." Research in animals and some in people suggests that the most dangerous type of stress comes with helplessness, such as "when you're a middle manager and can't change the system," he explained.

"When you're more in charge, it isn't a bad stress," he said.

Goodwin added that presidents aren't like other people. "You're selecting for people with tremendous life force, incredibly energetic, emotionally active and positive people," he said. "They're politicians."

One idea for future research would be to study the losers of presidential elections, who would share many traits with the winners but never actually ended up in the White House, he said.

The research is published in the Dec 7 issue of the Journal of the American Medical Association.

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(Agencies)

（中国日报网英语点津 Rosy 编辑）