On March 20, the eminent academic Rosemary Pope was found dead in her Bournemouth home. She was 49 years old, and weighed just four stone 10lbs. Pope, who had had anorexia since her teens, is thought to have collapsed after returning from a shopping trip - her left hand clasping a pot of creme fraiche. The stress of carrying the bags, coupled with a recent stomach virus, caused her frail body to finally give up. The creme fraiche was almost certainly a last-ditch attempt at an energy boost, but her heart - which, the inquest last week heard, had shrunk to the size of a child's because she had been starving herself for so long - gave out first.

Pope's story isn't just tragic, it is also - on the surface, at least - shocking. How could a renowned professor with an international reputation and a PhD in psychology find herself in the grips of a condition usually labelled a young woman's disease? How could someone have, on the one hand, an "unusually vivacious and outgoing personality" and a "robust sense of humour", and on the other be suffering a debilitating and severely malnourishing illness? And didn't anyone - her friends, family or colleagues - notice that this mature, professional woman was starving herself to death?

The reality is that Pope's story is becoming more and more common, with anorexia increasingly affecting older women. Like Pope, many of these women are extroverts who hold down good jobs and manage to survive in a very compromised state for years, even decades. "Ten years ago, there were very few women in their 30s, 40s, 50s and older who were diagnosed with anorexia. That has changed significantly, especially in the past five years," says Susan Ringwood, chief executive of Beat, the national eating disorders charity.

While there are no authoritative statistics, other specialist charities and clinics confirm that up to 10% of patients with anorexia are older women. In the US, says Trisha Gura, author of Lying in Weight: The Hidden Epidemic of Eating Disorders in Adult Women, "some treatment centres are reporting that 50% of patients are now 40-plus. One centre I talked to recently said it had more older women than younger ones."

While this rise may be partly due to increased awareness of anorexia across all age groups, experts believe that increasing numbers of young people with anorexia are growing older with the disease, as well as a significant number of women who develop it later in life. Experts blame, at least in part, the increased pressure on older women to stay young. Surrounded by images of women such as Madonna, Teri Hatcher and Jane Fonda (who has admitted to suffering an eating disorder herself), women are exposed to increasingly unrealistic images of how they should look as they age and are working harder than ever to counter the effects of getting old.

Nobody is suggesting that this alone is causing hordes of women to head down the potentially deadly path of anorexia. But if you are already prone to the other risk factors - low self-esteem, perfectionism, a need to be in control, among others - it is more likely, says Ringwood, particularly at times of change or stress.

While some women - and some men, although it is thought very few - develop anorexia for the first time in adulthood, others who conquered an eating disorder in their teens or 20s are finding it recurs when they hit their 30s, 40s, 50s or even 60s. "For much older women, the quality of treatment when they were teenagers was often very poor and has not stood them well for the rest of their lives," says Ringwood.

As Eileen Simpson, who, at 54, has had anorexia for most of her life, recalls, "My treatment at 17 was a matter of being put in a ward with long-term psychiatric patients - terrifying enough for a young girl - and being given heavy psychiatric drugs, insulin to increase my appetite and more and more food. Not a psychologist in sight. The object was to increase your weight and get you out. It was barbaric."

Simpson is among the third group of adults with anorexia, which includes Pope, who never managed to overcome their anorexia in the first place and simply grow older with it. "Rosemary's eating had been an issue from her teenage years," confirmed Pope's older brother, Michael, at the inquest. He described how she would take her own food when visiting family members or staying at hotels, and how she only appeared to eat processed food such as cheese, yoghurt, soft drinks and diet sweets. Last Christmas particularly stood out in his mind: "She laid on a feast which we couldn't possibly eat and she left the room while we ate," he said. She then returned when everybody had finished eating and threw the leftover food in bin liners and placed them outside the house. "It was only then that she appeared to relax."

After she died, it transpired that Pope had hoarded tinned food in her home and she had numerous food-related magazines. The shopping bags found with her dead body contained several such magazines.

Pope's brothers had tried to help. "Although we raised the subject with her from time to time, it was clear to us that it could damage our relationship with her and could be detrimental to her if we pushed too hard," said Michael. "She was unable to hear what we had to say."

At Bournemouth University, where Pope worked, it took a stomach bug in January - which caused particularly rapid weight loss - for anyone to say anything, and even then it appears to have been only one colleague. "Rosemary never looked that well, she did look very thin, but any concerns I had were about her workload and her tendency to worry about work issues," said Michael Riordan, human resources director at the university.

David Willey, deputy vice-chancellor, saw Pope on a daily basis and only ever saw her eat fruit or sweets. She wouldn't eat the sandwiches provided at university meetings, he told the inquest. "She would bring her own sandwiches on a plate under a napkin, but I do not recall her ever having touched them."

Other colleagues, and even friends, say they didn't know anything was wrong. Professor Pam Smith, who took over from Pope when she left her previous post at Surrey University, said she had no idea her friend had anorexia.

Her brother Michael isn't surprised. "Although she had suffered from an eating disorder for years, she was an enthusiastic, energetic and capable person. We find it hard to understand how she was able to carry on at all times without any interruption to her life or work, despite her low levels of nutrition."

In fact, part of the appeal of anorexia to its sufferers, particularly older ones, is the heightened mental state and sense of control that starving yourself can provide. At its core, anorexia is a need for control in response to an emotional state that feels completely out of control: food is just the means. Because people with anorexia often like food (think of Pope's magazines), they feel a sense of satisfaction when they abstain from it. The bottom line is that they don't feel they deserve it.

"Adults with anorexia can, like Rosemary Pope, be emaciated for years, but still function, and other people get used to them being like that," says Ringwood. "Add to this their heightened energy, a very driven personality and the fact that the general public still associates anorexia with adolescents and you can see how it can get missed by others. Even if people do suspect it, they often fear saying the wrong thing, or think that it might actually be cancer."

Also significant is the increasingly thin line between disordered eating, which has become normalised among many women, and eating disorders. As one 42-year-old woman with anorexia puts it: "If you see an extremely thin woman on the street, you might think 'anorexic', but put a pushchair in her hands, and you think, 'overworked mum.'"

Simpson, who is six stone, thinks her friends would be amazed if they discovered she suffered from anorexia. "They think I'm just fragile or have some physical condition I don't like talking about," she says. Another 34-year-old woman with anorexia confirms that she knows "people of a similar age to me who maintain their weight at around six stone to help prevent people from noticing. That's very common".

Deanne Jade, principal and founder of the National Centre for Eating Disorders (NCED), believes that adults often have a tougher fight on their hands in terms of recovery than their teenage counterparts. On a practical level, the condition (in particular its rituals, whether being sick, taking laxatives or over-exercising) becomes more entangled in the fabric of everyday life. "The older the anorexic, the stronger the identification with the illness," says Jade. "You can see it in the way they talk. If I said to them, 'If I had a magic wand that would make you OK with food, would you let me wave it?' many would hesitate. If I asked if that's because it would be giving up an important part of themselves, they'd say, 'No, it would be giving up my whole identity.'"

Many older people with anorexia see their illness as a place of safety from adult life. "In the absence of self-worth, the anorexia gives them a sense of purpose, of feeling special, of having status and most of all, it helps them avoid - through their control - the mess of life that the rest of us manage to cope with."

"I am reconciled now to never having a normal relationship with food," says Diana Brighouse, 53, a doctor who is married with four children and has had anorexia since she was 16, as well as suffering from bipolar disorder. "Although I'd love to be rid of my anorexia, I am not prepared to gain more weight. So I live in an uneasy compromise where, when I am really well I can happily go out and eat in restaurants, but at the same time have various 'rules' about food, like never eating lunch, forbidding various foods, having to exercise a certain amount and so on."

Brighouse believes people are remarkably oblivious to her illness. "The vast majority of my friends just think I'm naturally thin. I think that's largely because older women are much more clever about not drawing attention to it. While anorexic girls will cut up their half an apple and make it last a whole meal, older women are much more canny about appearing to have a plateful of food that actually only has 50 calories in it."

Despite her illness, Brighouse managed to breastfeed all four of her children for a year each, and she has worked in a professional capacity with women with eating disorders. "I have loads of professional insight into the condition and, of course, my personal experience. But unfortunately, it makes me no more able to manage myself," she admits.

"I belong to a support network for doctors in mental health and we have a high number of people with eating disorders," says Brighouse. "Anorexia is traditionally something that is most likely to affect high-achieving, pressured, academic, middle-class girls and those girls grow older, often going into professions such as medicine and academia."

Despite having developed anorexia in adulthood, Jane Morgan, 36, also can't imagine a non-anorexic existence. "I never had any issues with food when I was a child," she says. "But at 21, I felt sick of feeling responsible for everyone else's feelings and at the same time I felt quite chubby and unhappy. I went on a diet and kept going because I liked the feeling of control it gave me. There is a part of me that doesn't want to get rid of it. I do feel I can deal with things better if I don't eat enough. It's a bit like a drug. But the other part of me is fighting against it and sometimes I wish someone would just say, 'You've got a problem, you're coming with us.'"

This is unlikely, however, since Morgan, who is in a high-level management position, is able to hover no more than a stone underweight, keeping colleagues and even her husband from finding out. "He knows I used to have a problem but I lie to him about my eating now. If I'm sick, I don't tell him and sometimes I'll put food in a tissue and quickly stuff it in a mug. I lie because if I told the truth, he would worry and want to help, and he can't help."

In many cases, however, relations and family members of someone with anorexia are aware, but don't know how to help. Adult anorexics have the added risk of passing their food obsessions on to their children, points out Gura.

"That is the thing I regret the most about it all," says Alison Alden, 49, who developed anorexia in her early 40s. "I remember one night my son shouting, 'Mum's going to eat with us; she's really going to eat and she's really going to do it with us.' I was shocked that they'd been so affected." But she, in turn, believes she picked up on her own mother's issues with food. "She used to say to me, 'I don't like big women. Don't ever grow too big,'" she says. "I think I internalised these messages until I reached a point that I couldn't cope with life and then responded to them."

If you couple adult anorexics' reluctance to let go of their disease (or often even to admit to it) with their low self-esteem, you can see how a visit to the GP to say, "I think I deserve treatment," is an unlikely scenario. Even women who do approach their doctor ("My periods are irregular"; "I think I'm underweight"; "I think there's something wrong with my blood sugar levels" etc), are often overlooked. It's not because doctors are uncaring but, like the rest of us, they tend to stereotype anorexia as an adolescent problem. One woman who told her doctor she had dietary problems recalls being sent to a homeopath, whose colonic irrigation methods reduced her "to a crisp". Others are given antidepressants.

Even progressive GPs, of which there are many, often have their hands tied because specialist treatment is aimed at youngsters. The waiting rooms are designed to look like teenage bedrooms, and rules and guidelines are tailored to teenage patients.

Guidance from the National Institute for Health and Clinical Excellence says treatment for anorexia should be age appropriate. But according to Ringwood, this is usually translated as a need to focus on adolescents who, in the past, had their own needs overlooked. She is quick to point out that many adults do get better and it is worth seeking treatment, but it is only in the US that real headway is being made to ensure that older women don't get overlooked.

In Minneapolis, a centre is being set up exclusively for older patients. "Meanwhile, in North Carolina, there is some experimental work going into treatment for couples, in recognition of the fact that partners can be just as important in the recovery process," says Gura, who hopes that similar projects will be picked up in the UK.

Anorexia is not a common disease. It is estimated to affect 1% of adolescent girls and even fewer older women. But it is the most deadly mental illness, and it is claiming victims from an ever wider section of society. Wouldn't it be fitting if Rosemary Pope's legacy was to put these women on the radar in this country and wake us all up to the changing face of anorexia?

· Some names have been changed. b-eat.co.uk, 0845 634 1414; eating-disorders.org.uk, 0845 838 2040.