Anorexia is a long-term illness for a significant number of sufferers, a study shows.

Researchers followed up anorexia cases 21 years after patients' first admission for the condition and found 10% were still sufferers, while a further 16% had died of the symptoms.

About half of the 84 patients - all female and with an average age of 42 - had fully recovered from the condition, said Dr Stephan Zipfel and colleagues at the University of Heidelberg in Germany.

Patients who did not fare so well had a long duration of illness before hospitalisation, and psychosocial factors such as missed work days and binge-eating also played an important role.

People suffering from anorexia nervosa think constantly about food and calories and try to avoid eating. They are convinced that eating will make them fat, leading to teasing or verbal abuse from other people.

Causes of death

Among the causes of death were lung and blood infection, complications due to dehydration and electrolyte imbalance, and suicide.

One patient died from peritonitis after a small intestinal perforation, and two perished in "an extremely malnourished state".

The research team said in The Lancet medical journal that there were significant psychosocial differences between the different groups. The patients still alive after 21 years completed a psychiatric interview, physical assessment and psychological questionnaires.

Patients classified as "poor outcome" missed an average of 99 work days a year, compared with 40 days for the intermediate group and three days for the good outcome group.

A long period of illness before admission to hospital, and low body mass index - the relationship weight and height - were also important factors.

Patients who combined weight loss with binge-eating or "purging" were more likely continue to suffer from the condition than those who merely restricted their food intake.

Dr Zipfel, said: "The finding that a longer duration of illness and a low body mass index before first inpatient treatment were associated with a poor outcome emphasises the importance of early identification and intervention."