The strain shows through, but a stint in the White House may be the key to a longer life

Barack Obama: 44th President (2009-present)

Judging by their before and after photographs, US presidents appear to age before our eyes, adding wrinkles and grey hair with each year in office. But their time in the White House does not appear to shorten their lives, and most live longer than their peers, a new study has found.

S Jay Olshansky, a demographer at the University of Illinois at Chicago, became interested in the subject this year when President Barack Obama celebrated his 50th birthday. Media coverage focused on his greying hair and deepening wrinkles.

Mr Olshansky calculated how long US presidents would have been expected to live based on their age and the year of their inauguration and compared it with their actual life span.

He found that 23 of the 34 US presidents who died from natural causes did not appear to have their lives cut short by the stress of the job. In fact, they lived longer than men of the same age and era.

His study appears in the Journal of the American Medical Association.

Ageing effect: The price they paid for power

George H Bush 41st President (1989-93) Presided over first Gulf War. Served one term.

Bill Clinton 42nd President (1993-2001) Impeached and cleared over sex scandal.

Barack Obama 44th President (2009-present) Economic woes hit ratings.