Prenatal Exposure to Testosterone and Development of BN

A digital ratio provides a useful marker for children who may be at increased risk.

Prenatal exposure to testosterone has been linked to development of bulimia nervosa (BN). This has been shown in opposite-sex twin samples (Arch Gen Psychiatry 2013; 65:329; J Abnorm Psychol 2013; 122:420). As reported by Dr. Radha Kothari and colleagues in the American Journal of Human Biology (2014; 26:176), the 2D:4D digital ratio can be a useful marker of increased risk for developing BN.

The ratio of the length of the second and fourth digits of the hand (2D:4D) has been found to correlate negatively with fetal testosterone/estradiol ratios. Thus, a low 2D:4D ratio is associated with relatively higher levels of fetal testosterone, and a high 2D:4D ratio is associated with lower levels of fetal testosterone. Previous work in a community sample showed that having a comparatively high 2D:4D ratio (indicating low prenatal testosterone exposure), correlated with more disordered eating (Psychol Med. 2006; 36:359). In what is believed to be the first study to investigate prenatal testosterone exposure in children at high risk of eating disorders, the researchers used data from the Avon Longitudinal Study of Parents and Children (ALSPAC), a large population-based study, to evaluate a group of children whose mothers reported a lifetime history of an eating disorder (anorexia, BN, or both). www.adls.ac.uk/

Pregnant women and their fetuses were enrolled in the ALPAC study, and children alive at 1 year of age have been followed since that time. Mothers completed a questionnaire about their psychological history at 12 weeks gestation, including lifetime eating disorder history. Of the 11,088 women who responded, 446 reported having a lifetime history of eating disorders. At 11 years of age children had their hands photocopied and the length of their second and fourth digits were measured, and the 2D:4D ratio was calculated.

Children of women with lifetime BN were found to have lower 2D:4D ratios on their right hands in comparison to children of women with no history of BN, suggesting exposure to higher levels of testosterone while in utero. This effect was present in female children of women with BN, but not in male children of women with BN.

How testosterone levels affect eating disorders

The authors note that circulating female and male hormones have complex and significant effects on disordered eating—for example, estradiol diminishes eating (Expert Rev Obstet Gynecol. 2012; 7:573). Conversely, testosterone levels are higher in women with BN and testosterone-blocking drugs may diminish BN symptoms (Acta Psychiatr Scand. 1996; 94:137). In addition, polycystic ovary syndrome, (in which testosterone levels are high) has been linked to bulimic symptoms (Nat Rev Endocrinol. 2011; 7:219).

Gender differences in disordered eating have long been recognized; traditionally, the role of sociocultural factors has been emphasized to explain these differences. The results of this study add to the body of evidence implicating hormonal factors as explanation for a portion of these gender differences.