Three-quarters of the way into tea and chocolate tiffin cubes with Arianna Huffington, she admits she's a workaholic. And it is an admission, not a humble-brag, because Huffington's newest cause is to train herself and others not to work so hard, or at least not to work all the time, which is different. She's getting there, but it's difficult.

“I think it’s time to identify the snake in the Garden of Eden that is overconnectivity,” she says. “I’ve taken a lot of steps in my life. My bedroom in New York is a completely digital-free area. I don’t take my BlackBerry or my iPhone or my iPad to bed. I read real books in bed, and it’s just fantastic. It’s like, what can be so urgent?”

Huffington and her many devices are in London to host Third Metric, a conference with the subtitle "Redefining Success Beyond Money and Power" (money and power being the first two metrics), which takes place the evening after we meet at the sumptuous Charlotte Street Hotel, in Bloomsbury, close to the offices of the Huffington Post's parent company, AOL.

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Surrounded by chatter and the tinkling of the lobby piano, Huffington searches the menu in vain for decaf tea, toys with Darjeeling, then settles on Bespoke English Breakfast – the tiffin cubes are for me and John, an AOL corporate communications man. She tells me not to worry that I’m flying home before the conference: “We’re going to live-blog it.”

The Third Metric power-shindig is a follow-up to a similar “tribal” event she cohosted in the spring with her friend Mika Brzezinski, an MSNBC news presenter, in Manhattan, at the SoHo loft apartment she bought late last year for about $8 million.

“We took all the furniture out, and there were around 340 women there. But also my friends used their apartment above mine for the launch, and Jon Bon Jovi and his wife live on the top floor and we used their terrace for the reception. It became a bit like – in the States they call it a progressive, when you go from one apartment to the other,” she says. “And these were intimate issues we were discussing, about what we value in our lives, and how we live our lives.” Although the event was aimed at a female audience, there were “some good men” there too.

Huffington’s Third Metric preaches a combination of mindfulness and meditation; spiritualism, kindness therapy and practical steps for banishing or ignoring “ridiculous” 21st-century expectations that leave men and women exhausted and stressed by a sense of “time famine”. Her starting point is that success tends to be defined “in terms of money and power exclusively”, and that without a third metric, “it’s like a two-legged stool – you fall off”.

“If you look around, you see so many people in politics and media and business making terrible decisions. I think they are burnt out.”

Huffington had a burn out of sorts six years ago. “When I fainted in 2007 and broke my cheekbone and had four stitches on my right eye, it started me on this path of re-evaluating my choices,” she says.

Her choices up to that point had made her an undeniable success. Hers is a CV that confounds in its rich variety over the decades. How best to describe Arianna Huffington? “Blogging queen” doesn’t cut it. “Social climber”, another label that has been slapped on her over the years, is plain obnoxious. She has, at various times in her life, been an economics student, an author, a Manhattan socialite, a billionaire’s wife, a cable-show comedienne and a one-time participant in a gubernatorial race. On her Twitter bio, after her job title of “president and editor-in-chief of the Huffington Post Media Group”, she lists “Mother. Sister. Flat shoe advocate. Sleep evangelist”. She needs seven or eight hours’ sleep each night, which is perfectly normal, of course, even if the business elite so often profess to survive on much less.

Born Arianna Stassinopoulos, in Athens, in 1950, she left Greece as a teenager to study at Cambridge, where she became president of its debating society, the Cambridge Union. In 1971, she appeared as a panellist on the BBC's classical music quiz Face the Music, on which she met the late English journalist and broadcaster Bernard Levin, who was twice her age. They began a relationship.

The second thing she tells me, after she mentions they have just put a yoga room into the Huffington Post's Washington office, is that she used to visit Ireland – Wexford to be precise – in the 1970s, with Levin. They split up when she was 30. She wanted children, but Levin, by then in his 50s, did not, so she decamped to New York and entered a new social scene, marrying oil tycoon and Republican Michael Huffington, in 1986.

They moved to Washington so he could pursue his political career and had two daughters, Christina and Isabella. She became a US citizen, and he was elected to Congress, though his Senate bid failed. They divorced in 1997, Huffington disclosing his bisexuality shortly after, and her next stop was Los Angeles.

Somewhere along the line her political philosophy shifted quite firmly from conservative to liberal, and, in 2003, she ran (against Arnold Schwarzenegger) as an independent candidate for the governorship of California. When asked if she still retains any ambition to run for office, she answers “no” before the sentence is finished.

"No. I love my job now, because the great thing about the Huffington Post now is that whatever I dream, we can make it happen."

The eponymous site, filled by the work of both paid journalists and volunteer bloggers, effectively revelled in first-mover advantage when she co-founded it with three men, in 2005. Although it was sold to AOL in 2011 for $315 million, it remains Huffington's baby, and she has infused its proliferating number of international editions with her new Zen-like message. In Japan, where HuffPost's latest offshoot was launched, people are "rediscovering" meditation through the site, she says. Germany will be next to get a HuffPost.

AOL is investing hard, but it is not immediately clear where the Huffington Post will end up in the hierarchy of media brands in a decade's time, and I wonder afterwards if her passion for the Third Metric corporate-events scene might survive her direct involvement with the Huffington Post, with which she has already achieved so much.

She tells me the story of a speaker at one of her events who quit his job in the City and now runs a yoga company. Such journeys from rat race to lotus position are often dressed up as personal awakenings when bank balances are high. Huffington is aware that not everyone can control their own destiny to the same extent, and agrees that chief executives and others in the “boss class” have the power to prevent staff burnout and stress-related absenteeism. But self-help, by definition, is always about channelling inner resources, not promoting structural change.

“You know, you may say people are struggling with two or three jobs, but what the Third Metric means, whatever level you earn at, is to be able to tap into that place inside yourself where there is strength and wisdom,” she says.

This confusion of our priorities is largely self-inflicted, the way she tells it – it is our own inability to switch off.

“Technology has meant we feel we can never stop working. There’s no human being, there’s no stopping, there’s no weekend, or after work,” she says. “So I made a decision that people are not expected to answer emails after hours or at the weekend. If there is something urgent, we find them, we text them, we call them.”

Huffington’s mission comes with some ironies, not least of which is the fact that she works in the media, an industry not known for its willingness to acknowledge the benefits of recharge time – such niceties get in the way of the news cycle that turns so fast it leaves everyone dizzy. But the main irony is that her advocacy of a dialled-down work culture has itself become a new professional angle, placing her directly on the wellbeing circuit of the corporate world, and adding to her air miles. Airports are not calm places, I suggest.

“You make a decision to be frazzled at an airport,” she says. “Or you can be calm on the top of Mount Everest, if you choose to be.”

Notwithstanding her dislike of overconnectivity, Huffington’s stress-busting sideline is supported by an app, the cute-sounding GPS for the Soul, which assesses users’ heart rates by measuring the pulse in their index finger. It tells me I am “in sync” and “in balance” and invites me to enhance that feeling by sharing its preloaded spiritual guides with friends.

“I consider myself spiritual,” she says, when I ask her if she is religious. “I believe in God, I believe that life is not the end.”

Yes, “definitely”, she tries to live life without regret. “And no grudges,” she adds in her Greek-American drawl. “Holding onto resentments and grudges is incredibly draining.”

Her inspirations are high-level. She cites the writings of Marcus Aurelius. “You know the man was Emperor of Rome – it was a very stressful job,” she says, laughing. “And Viktor Frankl, who wrote about life in concentration camps; he wrote about how the one freedom nobody can take away from you is how you respond to your circumstances, whatever the circumstances.”

Her mother, who died in 2000, was “amazing”, she says, “speaking of inspirations”, and she helped her not to fall into the trap of measuring herself against her peers.

“She was a complete original. And she always taught my sister and myself not to judge ourselves on what others are doing, because that’s really the problem – you are basing success on what other people consider success, but it may not be your definition. And this whole, like, straight line, this straight career line, it’s a very male thin – it’s almost like a male phallic line,” she says, laughing.

After Facebook's chief operating officer Sheryl Sandberg published Lean In, her manifesto for female ambition, Huffington wrote a response piece that advised women to lean back before they lean in, because the male-dominated model of success wasn't working for anyone.

"I think the point that Sheryl Sandberg was making, which I believe in, is not to let our own fears get in the way of what we want," she says. "But the French have an expression – reculer pour mieux sauter, which means leaning back to jump higher. You need to lean back to recharge, to recover, and then pursue whatever it is you are doing, because if you are constantly leaning in, you will fall off."

Huffington’s sense of humour is an underexplored part of her public persona, perhaps because it seems secondary to her sharp-shouldered glamour, and yet comedy has been a consistent element of her portfolio career, and her charm is laced with wit.

In 1996, she was cast as "the right-winger" on Comedy Central's Strange Bedfellows, opposite the liberal Al Franken, and she also wrote for the late-night talk show Politically Incorrect, hosted by Bill Maher, who she describes as a friend. More recently, she has allied herself with Jon Stewart.

“My mother used to say that angels fly because they take themselves lightly. For me, it’s so often when we take ourselves too seriously that life gets harder, and when we can laugh at things, it’s just very liberating. Some of my greatest friends are satirists.”

The night before our interview she went to see one of them, actor and humourist Harry Shearer, in a weighty play called Daytona, and it's still on her mind. "That's the great thing about Twitter. He said, 'I see you are in London, I have a play here, come and see it,' so I went and it was very serious, very dramatic, and I am still affected by it – I woke up this morning feeling the play."

Without humour, there is “a danger of pomposity”, she says, and from mention of pomposity the conversation segues into the short-termism and blindness of today’s political figureheads.

Fiercely anti-austerity, Huffington reminds me of her academic background in economics as she insists that austerity does not work. “I mean just look around. I’m stunned. It is one of the things I find stunning. We have all the evidence in front of us that it hasn’t worked,” she says. “It’s like we have all these tools in our toolbox and we are not using them.”

Does she think that world leaders will eventually come to that conclusion and stop repeating the same mistakes?

“Well, you can never underestimate the stupidity of world leaders,” she says.

“My main problem is a lot of our contemporary leaders are underestimating the incredible cost we are paying in terms of human life when it comes to youth unemployment,” she says.

“For me that’s a real crisis, and we are underestimating the costs down the road of these people whose lives are interrupted . . . It’s hard enough living a life right after college, but when you can’t even get a job, when you have done everything right, it makes you distrust the society in which we live, and it’s harder to grow into an adult. We’re not taking it seriously enough.”

Huffington's daughters are now in their 20s and both have revealed intimate details about themselves. Isabella (22), now a senior at Yale, majoring in art history, wrote a blog – for the Huffington Post – about suffering as a teenager with anorexia, a time when getting her period was a sign of being healthy, but she didn't want to be healthy, she wanted to be skinny. Christina (24) struggled with cocaine addiction.

“She’s now been sober for a year-and-a-half, and she wants to spend a large part of her life helping other young women who have had similar problems,” says Huffington. “She wrote about it, which I was proud of, because I think it’s important to deal with this directly and not to be shamed into not discussing it.”

Huffington is single. “I have my work and my children, and I’m an evangelist for the Third Metric and people living their lives with less stress and more joy and gratitude. It is a thing that people so often forgot – to be grateful for what we have, you know? We focus on what we don’t have.”

She asks John, the AOL man, to take a picture of our meeting so she can tweet it, as she does with seemingly all of her engagements. The sun gleams through the window above her blow-dry, like an aura. Some rather chilled-sounding bells peel. It’s the ringtone on her BlackBerry – very “third metric”. She listens to it for a few seconds before answering. “Sorry, I’m needed on a conference call. Do you need anything else?”

I throw away my last question on the other part of her Twitter bio, “flat shoe advocate”. She’s not wearing flats today, but a kitten heel. “This is the highest heel I wear,” she says, turning it outward. It’s a question of appropriateness. “I was in Greece at the Special Olympics two years ago, and there were women climbing the Acropolis in high heels. There must be something about our sense of ourselves that we don’t feel adequate except in high heels.”

In her own executive whirlwind, there’s no time to waste on feelings of inadequacy.