Jacinda Ardern's burnout highlights the pressure world leaders face

Jacinda Ardern said she didn't have "enough in the tank" to continue as prime minister

New Zealand's Prime Minister Jacinda Ardern surprised the world this week, announcing that she was quitting because she no longer had "enough in the tank" to do the job.

"Politicians are human. We give all that we can, for as long as we can, and then it's time," she said in an emotional address that signalled the end of her five-and-a-half years in office.

It is unusual for a politician to admit they are burnt out - but it's not surprising that the stress of leading a country can take its toll.

World leaders enjoy many privileges, but they must often cope with constant travelling, long hours, and little time to relax.

Former New Zealand Prime Minister Helen Clark understands more than most the pressure of having a country's top job.

She recalls working "a tremendous number of hours a day" as prime minister for nine years, from 1999 to 2008.

Like Ms Ardern, she was based in Auckland and was constantly travelling to and from the capital city Wellington - an hour's flight away.

"That often involves a seven o'clock flight in the morning, so you might get up at five and then you might go to bed after midnight," she tells the BBC.

"On nights you stay in Wellington, you're probably still going to be up at daybreak and then maybe working to the wee small hours."

• Ardern: No regrets over decision

• Who is Jacinda Ardern?

• Why Ardern's star waned in NZ

Ms Clark says she tried to carve out time for herself at weekends as a way of coping with the demands of the job.

She says Ms Ardern appeared to have a "very, very demanding programme" - plus an extra layer of pressure from "balancing a family and career" at a time of major political challenges.

"I didn't have that particular pressure. I was in a position to be pretty single-minded about the job," she says.

In her announcement on Thursday, Ms Ardern said her partner and her daughter - whom she gave birth to while in office - had arguably "sacrificed the most out of all of us".

Ms Clark says it is important to have a strong support system to deal with the demands of the job.

"Jacinda has a very supportive partner and her parents have also been tremendously helpful in supporting her. But these have been very, very tough and unusual times.

"In a way the toll it's taken on her in five-and-a-half years is maybe a bit like I was feeling more towards the end of nine years," she says.

Ms Clark believes that while the pressure on leaders has "always been immense" it has become even more so "in the era of social media and the 24-hour news cycle and click bait and trolling and conspiracy theorists and the rest of it".

Helen Clark (seen with Jacinda Ardern in 2017) was New Zealand's prime minister for nine years

British historian and political biographer Sir Anthony Seldon agrees.

"Objectively the pressures have grown and grown," he says.

"It's a huge set of burdens coming in and it all comes in on the desk of the leader. They only have the same number of days in the week and hours in the day as everybody else. And they need to sleep and rest like everyone else… [but] the expectations are going up and up and up."

It is more common for leaders to be forced out than to admit they have burnt out, but there are several examples of political figures publicly struggling with the demands of recent years.

Ms Ardern cited the coronavirus pandemic as one of the main challenges she faced during her time in office.

In March 2020, the minister leading the Dutch government's fight against coronavirus resigned after collapsing during a parliamentary debate. Bruno Bruins said he had fainted after weeks of intense work.

In a later interview, he said that after leaving the role he had "slept for three months" before embarking on a new career outside of politics.

During his time as a minister, "at some point I kept waking up at 4am... After I collapsed, all I wanted to do was sleep", he told RTL Nieuws.

Austria's health minister Rudolf Anschober stepped down the following year, saying he was "overworked and exhausted".

"In the worst health crisis in decades the republic needs a health minister who is 100% fit," he told reporters at the time. "That is not currently me."

His 15 months in office had "felt like 15 years", he said.

Following the news of Ms Ardern's resignation, Estonian leader Kaja Kallas told the BBC: "[It] personally resonates with me. I totally understand the toll it takes."

Daryl O'Connor, a psychology professor at the University of Leeds, says that "one of the major contributors of burnout is work stress".

Burnout can affect anyone from nurses and doctors, to athletes, teachers and parents.

Dr O'Connor says that for a prime minster, the stress will be "unrelenting".

"Most other people can switch off in their daily lives, which will also allow their stress response systems to switch off. People in the public eye in highly demanding jobs such as being prime minister of a country don't have that luxury," he says.

Political biographer Sir Anthony, whose work has chronicled the lives of numerous British leaders, says many prime ministers finish their time in office exhausted.

"You cannot ever forget - on Christmas Day, your birthday, at 4am; you have to be on the ball all the time," he says.

"The truth is that many are not up to it, but very few admit it."

Following her announcement, many commended Ms Ardern for her honesty.

The former UK Secretary of State for Education and Skills Estelle Morris says Ms Ardern's announcement took her back to her own high-profile resignation 20 years ago.

"I'm not claiming for one minute I'm in her category but the feelings were something I recognised," she says.

In her resignation letter in 2002, Baroness Morris said she did not feel she had been "as effective" as she wanted.

"I knew what I was good at in the job. And when you feel that there's a set of circumstances around that mean you can't use those strengths as well as you used to be able to… I think you should be honest with yourself about it," she says.

"Jacinda explained that she loved the job and that it was really important but she couldn't do it at the moment… That's exactly how I felt."

Baroness Morris adds that it is a "type of strength" to know when to step away.

"Changing jobs in 2023 is not an unusual thing. It's just unusual when you've got that amount of power, that's why it's noteworthy," she says.

Ms Ardern said she was looking forward to spending more time with her family - being there when her daughter starts school and "finally" marrying her fiancé, Clarke Gayford.

For people hoping for a future life in political leadership, Ms Clark warns that the top job is "a lot of grind" and requires a belief "that it is worth the time and effort and long hours and that you can really achieve things".

"If you get to the point where you think 'this is not doing it for me' then you walk away," she says.

Ms Ardern said she was looking forward to "finally" marrying her partner Clarke Gayford