U.S. presidents live longer than their peers, a finding that differs from conventional wisdom that being a U.S. commander-in-chief wouls speed up aging, according to a new study.

"Just because they experience what would appear to be accelerated aging outwardly, doesn't mean they will die any sooner," said S. Jay Olshansky, a demographer at the University of Illinois at Chicago, according to Reuters.

His study is published in the Journal of the American Medical Association.

Olshansky states that despite the easily observed signs of aging halfway through the first term, 23 of the 34 presidents who died of natural cases lived several years longer than expected according to the life expectancy data for men who born in the same year as their presidents.

Stress can be manifested by outward signs of aging, and it’s likely that occupational stress has sped apparent signs of aging in some presidents, however earlier signs of aging do not mean an earlier death.

Many Obama “before” and “after” pictures in the media focusing on the 44th U.S. president’s graying hair and developing wrinkles tend to suggest that presidents age faster, implying that they died sooners as well.

"The graying of hair and wrinkling of skin seen in presidents while in office are normal elements of human aging; they occur for all men during this phase of life and can be accelerated by behavioral risk factors such as smoking and stress," he wrote. "Whether these outward changes occur faster for presidents relative to other men of the same age is unknown."

Olshansky mentions that a common theory about presidential aging is that each year in office accelerates aging by two years in his analysis.

Olshansky inspected ages of inauguration and death for every U.S. president who died of natural causes, as well as the current age of living past presidents. Depending on the duration of the each president’s term, Olshansky used the accelerated aging theory to approximate the presidents’ projected lifespan and compared those with the life expectancies of typical men from 1789 to present day.

He found that the average life span for all men in the entire study was 73.3 years, and the average lifespan for the 34 dead presidents was 73 years. He said that if the accelerated aging theory was correct - that presidents in office aged at double the speed of normal men, then the mean age of death would have been 68.1 years.

According to Olshansky his analysis suggests that all four of the former presidents, still alive, have either exceeded or are expected to exceed the average life span of U.S. men.

Olshansky used his formula to predict that Obama’s age of death would be around 78 or 79; George W. Bush and Bill Clinton at 83; George H.W. Bush at 93, and Jimmy Carter at 92.