By Helen Albert, Senior medwireNews Reporter
Results from a study carried out in identical and nonidentical twins suggests that a woman's risk for thin-ideal internalization may be genetic.
Compared with a twin that had thin-ideal internalization, the researchers found that identical siblings were more likely to display the same psychologic trait than fraternal siblings, suggesting a genetic basis for this tendency.
"We're all bombarded daily with messages extoling the virtues of being thin, yet intriguingly only some women develop what we term thin-ideal internalization," said lead author Jessica Suisman (Michigan State University, East Lansing, USA) in a press statement.
"This suggests that genetic factors may make some women more susceptible to this pressure than others."
To investigate the influence of genetics on thin-ideal internalization, which can lead to eating disorders such as anorexia nervosa, Suisman and colleagues recruited 343 postpubertal female twins aged a mean of 17.6 years (12-22 years). Of these, 205 were identical and 138 non-identical.
Thin-ideal internalization was assessed using the 9-item, general, thin-ideal internalization subscale from the Sociocultural Attitudes toward Appearance Questionnaire-3.
Writing in the International Journal of Eating Disorders, the researchers found that identical twins with thin-ideal internalization were significantly more likely to have a sibling with the same trait than nonidentical twins.
Further investigation suggested that the heritability of this tendency is approximately 43%, indicating that genetics plays a large part in influencing a women's risk for developing thin-ideal internalization and associated eating disorders.
Of note, the results also suggested that individual environment plays a more significant role in the development of this trait than exposure to wider cultural attitudes such as those seen on television or in magazines.
"We were surprised to find that shared environmental factors, such as exposure to the same media, did not have as big an impact as expected," said Suisman. "Instead, non-shared factors that make co-twins different from each other had the greatest impact."
Study co-author Kelly Klump, also from Michigan State University, commented: "This study reveals the need to take a similar approach to the ways in which women buy in to pressure to be thin, by considering how both genetic and environmental factors contribute to the development of thin-ideal internalization."
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