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Having Female Twin Raises Risk of Anorexia
> 12/7/2007 1:27:22 PM

Females are much more likely to develop anorexia than males, a differential that is often attributed to social pressures and unrealistic ideals of female beauty. While such pressure undoubtably exists, a study published in the most recent issue of the Archives of General Psychiatry presents strong evidence that anorexia risk can be elevated by environmental factors in the womb. If true, this means that some people are predisposed to an eating disorder before they see their first supermodel or recognize their bodies in a mirror.

Dr. Marco Procopio took advantage of the Swedish Twin Registry to test a hypothesis that the sex of one twin can elevate the anorexia risk of the other. This type of link may sound farfetched, but many previous studies have confirmed that such connections exist. A 1985 study showed that opposite-sex twins displayed a blended male and female phenotype, in this case a jaw structure that was midway in size and could not be accurately assigned a sex by third-party researchers. Three years later, Dr. Cole-Harding showed that the sex of the other twin influenced not only physical characteristics, but also cognitive function. Females, who as a sex have lower averages on spatial tests, performed much better if born alongside a male twin.

In the study published this week, Dr. Procopio found that males were significantly more likely to develop anorexia if they had a female twin. Female-female twin pairs had the highest rates of anorexia, while male-male pairs had the lowest. As previous studies have shown that risk of anorexia does not correlate with the sex of siblings that do not share a womb, it is unlikely that this effect can be explained by social interactions after birth. Dr. Procopio conjectures that the presence of a differently sexed twin introduces hormones that a fetus would not normally be exposed to. The elevated risk of female-female pairs could be the result of abnormally high levels of a hormone that is supposed to be present but at lower levels. Future studies will have to determine exactly which estrogens and androgens contribute to this phenomenon. Once the relevant hormones are identified, parents and doctors will have not only a better insight into the nature of anorexia, but also a valuable forewarning of which children face the highest risk of developing a deadly eating disorder.

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