Males with a female twin may be at risk of developing an eating disorder later in life, according to a report published in the December issue of Archives of General Psychiatry.

The finding supports the theory that exposure to female sex hormones in the womb may be related to the risk for anorexia nervosa, the study's authors say.

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While many experts cite psychological factors as the cause behind anorexia -– it’s still not known why females are 10-times more likely than males to develop the disorder.

Dr. Marco Procopio, from the University of Sussex in England, teamed up with Dr. Paul Marriott from the University of Waterloo in Canada, to analyze data from a study of thousands of Swedish twins born between 1935 and 1958.

Overall, female twins were more likely than male twins to develop anorexia. The one exception was among males who had a fraternal twin sister.

“A plausible explanation for this phenomenon is that in pregnancies bearing a female fetus, a substance is produced, probably hormonal, that increases the risk of having anorexia nervosa in adulthood,” the researchers said in a news release. “Because the male half of an opposite-sex twin pair would also be exposed to this substance, it could account for the observed elevated risk in males with female twins. The most likely candidates are sex steroid hormones.”

“The results of our study are compatible with the hypothesis that intrauterine exposure to sex hormones might influence neurodevelopment, affecting the risk of developing anorexia nervosa in adult life,” they concluded. “This might be a factor contributing to the higher risk of developing anorexia nervosa in females.”

About 11 million Americans suffer from the eating disorders anorexia or bulimia nervosa.