LONDON -- Leading a country comes with extraordinary privileges but also, apparently, a price: new research suggests that heads of state age faster than normal and that the stress of the job may shave almost three years off their life expectancy.

Doctors analyzed how long presidents and prime ministers in 17 countries -- including Britain, Canada, France, Germany and the U.S. -- survived after leaving office, compared to the losing candidates. They also observed the number of years that heads of state lived versus what was expected for someone of the same age and gender.

After considering the fates of 279 heads of state and 261 runner-ups, they concluded former leaders lived for almost three fewer years than expected. The study was published online Monday in the medical journal, The BMJ.

"To lose a few years is significant," said Dr. Anupam Jena of Harvard Medical School, the study's senior author.

"(Leaders) probably felt national priorities were much more pressing than eating right and exercising," he said, saying former U.S. President Bill Clinton's admitted weakness for fast food may have resulted in "stress eating."

"Maybe if there had been world peace, his lifestyle would have been different," Jena said.

After leaving office, Clinton had bypass surgery; he subsequently said he lost weight and became vegan to try to reverse his heart disease.

Other researchers have found that U.S. presidents actually live longer than their constituents.

"The stress (of leading a country) could accelerate the greying of hair and wrinkling of skin, but that doesn't mean they'll die earlier," said S. Jay Olshansky, a professor at the University of Illinois at Chicago.

His research on former commanders in chief found they had a longer-than-expected life expectancy, partly because they are part of the top 1 per cent of the population that are highly educated, wealthy and have better access to health care than most.

Still, even U.S. President Barack Obama recently joked with Canada's new Prime Minister Justin Trudeau -- who is about a decade younger than Obama -- about how a country's top office can speed up aging. Obama advised Trudeau he should start dying his hair to avoid going grey.

Jena said Trudeau -- who is a keen outdoorsman -- might fare better than expected.

"Someone like him, who is fit, may be in a better starting position than others," he said. "The years could be kinder to him."