Research suggests that young adult women exposed prenatally to testosterone have a reduced likelihood of developing eating disorders. The finding, researchers say, provides further evidence that biological factors — and not just social influences — are involved in anorexia and bulimia.
In an ongoing study of 538 sets of twins in Michigan, researchers observed that females who were in the womb with male twins have lower risk for eating disorder symptoms than females who were in the womb with female twins.
Previous research has shown that females in the womb with males are exposed to higher levels of testosterone, Dr. Kelly L. Klump and colleagues from Michigan State University in East Lansing explain in the March issue of the Archives of General Psychiatry.
“From these findings, it appears that testosterone exposure could have a protective effect against the development of disordered eating,” Klump noted in a university-issued statement.
Women are more apt to develop eating disorders than men, perhaps due to social influences such as thinness ideals aimed largely at women. But the question of whether biological influences also play a role has not been well studied.
To investigate, Klump’s team studied data on twin pairs enrolled in the Michigan State University Twin Registry — 304 same sex female twins, 59 opposite sex female twins, 54 opposite sex male twins and 165 same sex male twins — and a control group of 69 women who were raised with at least one brother. Ages ranged from 18 to 29 years.
They assessed levels of disordered eating using the Minnesota Eating Behavior Survey, which includes measures of body dissatisfaction, weight preoccupation, binge eating, and compensatory behavior such as purging to control weight.
“Importantly, these types of disordered eating symptoms have shown robust sex differences,” note Klump and colleagues, ”with females exhibiting significantly more of these symptoms than males.”
The investigators observed a linear trend of average disordered eating scores, with same sex female twins — those with the lowest level of prenatal testosterone exposure — showing the highest levels of disordered eating, followed by opposite sex female twins, opposite sex male twins, and same sex male twins.
Anxiety only partially mediated the associations between co-twin’s sex and disordered eating, the researchers report, and in fact the opposite sex female twins showed lower levels of disordered eating than women raised with brothers.
While pressure for thinness in women has typically been used to explain the sex difference in eating disorder prevalence, “our results suggest that the masculinizing effects of prenatal testosterone, characteristic of male development, may also play a significant role,” the team concludes.
