An international study concludes that the eating disorder anorexia nervosa, a rare but dangerous mental condition, is primarily genetic in origin.
The study also found that a tendency to be anxious and depressed, or neuroticism, early in life is a strong predictor of having to battle anorexia years later.
The collaborative study of more than 31,400 Swedish twins by researchers at the University of North Carolina at Chapel Hill and at the Karolinska Institute in Stockholm, estimated that 56 percent of the liability for developing anorexia is determined by heredity.
“Fifty-six percent heritability — that’s a fairly large contribution of genes,” said Cynthia M. Bulik, lead author of the report published in this month’s issue of Archives of General Psychiatry.
The study is the first published in medical literature that has been able to estimate the key role inheritance has in the likelihood of developing anorexia nervosa — an illness characterized by a person’s intense fear of weight gain and a refusal to maintain a minimally acceptable body weight.
The condition was big news in 1983, when Karen Carpenter, 32 — a pop singer who, in the 1970s with her brother, Richard, had hits such as “We’ve Only Just Begun” and “Close to You” — died of cardiac failure resulting from anorexia. Obituaries at the time told how fans who attended her concerts sometimes gasped in horror when they saw the emaciated figure on stage.
Ms. Bulik said anorexics also tend to exercise far more than they should.
“You might hear of a person weighing only 50 or 60 pounds who is running five miles per day,” she said yesterday in a telephone interview.
Anorexia nervosa is most prevalent among women in their teens and early twenties.
“But it is surely getting worse” among older women, Ms. Bulik said. She indicated 40 percent to 50 percent of the women she sees with anorexia today at UNC’s eating-disorders clinic are older than 30.
Ms. Bulik said her study was also the first research to find a statistically significant relationship between neuroticism and anorexia. Other potential risk factors such as excessive exercise, excess stress and gastric difficulties — that have been cited in earlier literature, were examined in this study, but were not found to be predictive of anorexia.
Ms. Bulik stressed that her work is not complete and that she wants to find out exactly what is inherited that puts someone more at risk for anorexia.
“We suggest there are some basic biological differences between people with anorexia nervosa and everybody else,” she said, adding, “When most of us get hungry, or starved, we get more anxious. But these peoples’ bodies respond differently. They say that food deprivation makes them feel more calm and more in control, which is one reason they keep doing it.”
Cases of anorexia were identified as those who met the criteria for the disease as described in the American Psychiatric Association’s Diagnostic Statistical Manual of Mental Disorders IV.