What's up with Nicole?

Even by Hollywood standards, she has always been slender. But, with her size six trousers hanging loose over her hips, and not even the hint of a curve where once there was a perfectly sculpted alabaster cleavage, it is clear that Nicole Kidman has lost a disturbing amount of weight.

Emerging from a yoga class in New York, the 36-year-old actress is, indeed, skinnier than she has ever been.

Associates say that, at 5ft 10in, she weighs only 8st 3lb. Several friends are concerned that she is dieting and exercising more than is healthy, and others wonder what can be behind the change.

One old friend, who remarked after embracing her recently that she was nothing but skin and bone, was told with a wan smile: 'Perhaps I have been overdoing it a little.'

She certainly takes vigorous exercise. As well as her regular yoga classes near her rented penthouse in the SoHo district, she swims and jogs often. Recently she was seen jogging in a tracksuit, hat and gloves in a temperature of 30c.

Although her defenders say they have seen her dining on sea bass, or tucking in to chocolate ice cream, there are allegedly times when she prefers vegetable smoothies to a meal.

Currently her body mass index - expressing weight in relation to height - stands at just 16. The healthy range is 20 to 25, and doctors become concerned if it drops below 18. She is, then, clinically underweight.

Because she is so tall, the loss of 15lb since her marriage to Tom Cruise ended two-and-a-half years ago is clearly apparent.

Her agents, however, talked last night about her being happy and healthy, and vigorously denied any suggestions of an eating disorder.

Catherine Olim, her spokesman, said: 'Nicole has always been slender. Look at American Vogue, she is glorious. I don't know what the fuss is about.'

Those protests are given credibility by a 40-page spread in the magazine she refers to, which hit newsstands this week. Miss Kidman looks stunning, posing in clothes by a string of designers. ('She has the most perfect figure,' coos Valentino.)

Her influence in the fashion world is so great that she is shortly to be unveiled as the international face of Chanel No 5 perfume.

In media terms, she has blossomed since splitting from Cruise; it is fair to say that she has never been in such demand.

But the question many are asking is why Nicole, who has relocated to New York with her two adopted children, Conor and Isabella, is looking so tired and nervy? And why, they are wondering in Italy, has she pulled out of the Venice film festival? And why, they wonder in Hollywood, has she turned down a £10million payday - the biggest of her career - to star in a film opposite Brad Pitt?

There are signs that Nicole - who said in the spring that she feared a 'burnout' - is under a considerable amount of pressure, both emotional and professional.

She is still alone, despite a fling with rap star Q-Tip and a flirtation with rock star Lenny Kravitz, from whom she is renting a penthouse while her own pad in the city is renovated.

Her romantic friendship with Russell Crowe has foundered, and he has now married his onoff girlfriend Danielle, who is expecting a baby.

How painful this must be for Nicole, who longs to have a baby herself. She was, by her own admission, almost overwhelmed by grief when she had a miscarriage only six weeks after her marriage to Cruise ended.

Those who know her best say that she is still puzzling over the wreckage of that marriage and trying to come to terms with the feelings of abandonment and rejection which resulted.

'I don't think two people could have been happier than Tom and I,' she mused. 'He swept me off my feet and I fell madly, passionately in love. I was consumed by it. And I was desperate to have a baby with him. That's what I wish I'd done.'

Her vulnerable state of mind is not helped by a recurrence of the insomnia which has plagued her for much of her adult life. Furthermore, she has been driven to the brink by film roles about rejected, depressed and oppressed women - with whom she identifies to a remarkable extent. In an interview she said that she hesitated to play the suicidal Virginia Woolf in The Hours, because she feared the effect on her own state of mind.

'I wasn't sure I could go through with it. Virginia Woolf's unhappiness was just too similar to my own. I was afraid to do it because I thought it would be too painful,' she said. 'But I think characters come into your life sometimes because they're meant to ... I was able to use her and her knowledge.'

There are signs that she is no less troubled currently on the set of Stepford Wives in New York. The crew are said to be muttering about delays because she does not want to film outside in strong sunshine.

Her representatives say this is utter nonsense. 'No one is more professional than Nicole,' they aver, sternly.

But whatever the truth of those reports, one does wonder whether the film - a remake of the Seventies classic, about a town where wives are replaced by compliant domestic robots - has uncomfortable resonancesfor Nicole, whose Catholic beliefs were put aside by her Scientologist husband, and who, during her marriage, lost her identity in his.

What she yearns for is love - the love she gave to Cruise and which she still feels for him. 'I've said to Tom, I will be there for him for the rest of his life, always,' she said earlier this year. 'Tom and I had 11 years together. Your heart has to stay loving.'

She surprised everyone by admitting at the Cannes Film Festival that she would give up her career for love.

'I won't do this for the rest of my life, there's other things that interest me,' she said. 'I think when I fall in love, I'll stop doing as much of this because I want to settle down again.'

What she has experienced since then, though, are little more than dangerous flirtations.

Q-Tip, her escort at the premiere of The Hours, appeared to have been chosen because he is as unlike her former husband as it is possible to be.

KRAVITZ, meanwhile, took her to Puff Daddy's birthday party - again an event which would be anathema to straitlaced Cruise. In private, Nicole talks a great deal about concentrating on her children and trying to 'make it up to them' - she feels immensely guilty about the divorce.

She also complains that she would like to find a man with whom she could have an intelligent conversation.

The Jude Law episode - when she was falsely accused of breaking up his marriage - was bruising and she felt humiliated that anyone would think she would steal another woman's husband. Their meetings on both sides of the Atlantic were professional. In short, she remains steadfastly but unhappily single.

What a pity, for this is surely the golden period in Nicole's professional life. She took the Best Actress Oscar this spring for The Hours.

Later this year Cold Mountain, the Civil War epic directed by Anthony Minghella, will be released, and there is already an Oscar buzz forming about this bleak film. Also later this year she will be seen in The Human Stain, opposite Sir Anthony Hopkins.

Then there is Birth, a film about a grieving widow, which she made early this year, and after that Stepford Wives, scheduled for release next year.

Because of delays in filming Stepford Wives, she has had to pull out of the Venice Film Festival, and because of the promotional schedule of Cold Mountain she has had to pull out of Mr and Mrs Smith, opposite Pitt.

Her diary is indeed creaking at the seams. And she is determined to make the most of her status while she can, despite the insecurity which leads her sometimes to fear taking on projects in case she is not good enough.

'There was a time when part of me didn't really want to take on too many projects because I had other priorities like my marriage and my family,' she said earlier this year.

'Now I feel more confident. Also I find with two children that are older, that allows me a bit more time to devote to making films.

'They don't need you every five minutes and they spend time with their father.

'In any case I'm a pragmatist, and I won't always be offered these opportunities. Work while you can, I say.'

She is living very much the burnout life which she described in Cannes this year, travelling constantly and working hard. 'You give so much of yourself and you've got to step away at some stage. You can't do it for ever,' she said.

Could it be that the worryingly slight figure that emerged this week is evidence she is reaching the point of no return?