In September 1919, President Woodrow Wilson embarked on a cross-country tour to gain support for the Treaty of Versailles and his League of Nations. The grueling schedule required him to give as many as three speeches a day, and at the end of the month he collapsed after a presentation. When Wilson returned to Washington, D.C., he suffered a massive stroke, which left him partially paralyzed on his left side.

Although most presidents do not experience such extreme stress-related illnesses while in office, many do show signs of wear and tear. Wrinkles etch their faces and gray hairs become plentiful. Some say that while in office, presidents age twice as fast as a regular man.

"We know in the world of biology that you can't actually measure the aging of an individual," S. Jay Olshansky, PhD, told "There isn't any single test that you can take."

Olshansky, a professor of public health at the University of Illinois at Chicago and an expert in aging, examined statistics about 34 presidents who died of natural causes.

He looked at standard life tables and the dates of each president's birth and inauguration and compared the presidents' ages at inauguration with men the same age, to determine how long the presidents should live. To counter the argument that commanders in chief age two days for every one of a regular Joe, he subtracted two days for each day a president was in office.

On average, presidents who die of natural causes lived 73 years compared to 68.1 years they would have lived if they did age faster. From Herbert Hoover through Ronald Reagan, presidents have far exceeded their expected ages. Seven of the eight presidents survived longer than expected, including Franklin Roosevelt (at left), who died at 63 after serving 12 years in office. (The exception was Lyndon B. Johnson, who died at 64 of heart disease.) Four presidents have lived into their 90s: Gerald Ford, 93.5; Reagan, 93.3; John Adams, 90.7; and Hoover, 90.2. And the first eight presidents of the United States lived until an average age of 79.8 when most men were dying at 40 years or younger. (Reader Peter makes a good point below.)