Osteoporosis, once seen as the preserve of the elderly, is showing up increasingly in young people. A study conducted in Trinity College links it with anorexia, writes Grania Willis
Recent revelations that Hollywood superstar Nicole Kidman could be suffering from osteoporosis have shocked fans of the increasingly slender Australian actress, but it's a potent reminder that the brittle bone disease is no respecter of age. At 37, Kidman would seem to be far too young to be afflicted by a disease that is widely accepted as a post-menopausal concern, but low caloric intake can dramatically reduce the age profile of sufferers.
Anorexia and osteoporosis may seem, to the lay person at least, to be diseases that affect opposite ends of the age spectrum. But a four-year study conducted at Trinity College Dublin, the results of which are to be published later this year, reveal that the two are strongly linked.
"We have 20-year-old anorexics presenting with spontaneous vertebral fractures due to low bone-density as a result of amenorrhoea this_is_a_left_sq_bracketloss of periods]," says Prof Moira O'Brien, president of the Osteoporosis Society of Ireland and former head of the Anatomy Department in Trinity.
She conducted the study with Bernard Donne, director of the Human Performance Laboratory and senior experimental officer in Trinity's Physiology Department.
"The myth is still that osteoporosis is an old women's disease," Prof O'Brien says.
"So it's quite frightening at 18 to 25 to be told you could end up in a wheelchair or in a nursing home sooner rather than later. It didn't worry them when we told them they could die as a result of their eating disorder, but the prospect of hip fractures did. I believe in frightening people if it's going to save them."
So those unnaturally thin limbs that mark out the anorexic, whose distorted body image can only appear fat, are literally as frail as they appear and the symptom of another potentially deadly disease. Osteoporosis is showing up in younger and younger patients and Prof O'Brien has treated an anorexic child of 10 who showed a markedly reduced bone age and is already at risk of osteoporotic bone fractures.
Amenorrhoea, brought on by malnutrition, is caused when the caloric intake is so low that the pituitary gland thinks the body is starving. Production of the female sex hormones oestrogen and progesterone is reduced or ceases altogether, periods stop and increased bone-loss can occur.
When this happens at a time when the adolescent body should be laying down bone, the anorexic patient fails to reach normal peak bone mass. The combination of increased bone-loss and inadequate bone-formation means that the patient becomes osteoporotic much earlier than the traditionally accepted age profile of the disease.
Normal bone requires normal levels of the sex hormones - oestrogen and progesterone in women and testosterone in men. Decreased levels of the sex hormones put bones at risk and also cause excessive production of the naturally occurring stress hormone cortisol, which increases bone-loss still further.
Young bone in children aged between eight and 12, just before the growth spurt and the onset of adolescence, is much more responsive to growth if stimulated by exercise. Unfortunately, this can all too easily become part of the vicious cycle of anorexia, with excessive exercising to maintain a low body-weight exacerbating the threat to bones.
Prof O'Brien, who started working with athletes before the 1980 Moscow Olympics, found that over-training and insufficient nutrition was resulting in stress fractures due to loss of bone density and, in some of the female athletes, amenorrhoea
It's a scenario that is becoming increasingly familiar to Prof O'Brien and Bernard Donne, with the anorexic study revealing inadequate nutrition and over-training as two of the chief causes of bone-loss.
Conversely, asthmatic children are also at risk as the use of steroids to treat their condition can result in decreased bone density, made worse by lack of exercise.
An adequate caloric intake for the amount of exercise undertaken is vital to maintain bone health. Calcium and vitamin D are obviously necessary, but Prof O'Brien stresses that first-class proteins - such as meat and dairy products - are also important as they contain the essential amino acids and enzymes needed to form bone.
Vegetarians - and many anorexics start by cutting meat out of their diet in a bid to lose weight - are also in danger of decreased bone density as their high-fibre intake can cause increased intestinal motility or intestinal hurry as nutrients are flushed out before the body has adequate time to absorb them. The same is true for many coeliacs, whose symptoms include diarrhoea and therefore loss of nutrients.
Caffeine, alcohol and cigarettes - all of which tend to feature on the anorexic patient's daily intake - can also cause decreased bone density. Many anorexics additionally suffer from depression and, adding to an already bleak picture, some anti-depressants can contribute to bone loss.
Sponsored by the National Osteoporosis Society (NOS) in Britain, the Trinity study involved 56 control and anorexic volunteers aged between 18 and 35. The anorexic patients were referred to Trinity by either dieticians or the eating disorder group, Bodywise.
Once accepted onto the study, the anorexic patients were immediately put on oestrogen replacement therapies - HRT - to rebalance their hormone levels and help improve their skeletal health.
"If they can admit they have anorexia, it's the first step in recovery," Prof O'Brien says. "The most important thing for them to realise is that they have a problem. There are no symptoms until they break something, so it's vital that they have a bone-density scan to identify potential problems and help prevent fractures now and later in life."