Science and society. Debating a testosterone "sex gap".

S exual dimorphism of testosterone (T) in elite athletes was at the center of a recent case at the “Supreme Court of Sport,” the Court of Arbitration for Sport in Switzerland, after teenage Indian sprinter Dutee Chand challenged a sports policy regulating competition eligibility of women with naturally high T. The idea of a “sex gap” in T is a cornerstone of this policy ( 1). Policymakers infer that men’s higher T is the “one factor [that] makes a decisive difference” between men’s and women’s athletic performances ( 2)—so that women with naturally high T may unfairly enjoy a “massive androgenic advantage” over other women athletes ( 2). We report on an emerging scientific debate about whether the sex gap in T applies to elite athletes. In 2011 and 2012, respectively, the International Association of Athletics Federations (IAAF) and the International Olympic Committee (IOC) adopted controversial policies that regulate levels of natural T in women athletes ( 1, 3). The IAAF policy sets a ceiling for women of 10 nmol/liter in blood, which it identifies as “within the normal male range,” whereas the IOC policy targets levels “within the male range” ( 1, 3). Women with high natural T, according to the IAAF, have an unfair advantage over women with lower natural levels ( 1). Unless they are androgenresistant, women must lower their T in order to continue competing ( 1), which would require surgery or antiandrogens ( 4). Appealing her exclusion under the IAAF policy, Chand told the Indian Express “At every level of my life ... I have competed the way I am. I’ve been told the hormonal issue with me is natural so that’s why we have decided [to appeal]” ( 5). Her March appeal was the first formal challenge to the policy; a decision is forthcoming. The T policy is the latest attempt to use a biological marker to draw a bright line between women and men for sex-segregated sports. Decades of sex testing of all women athletes relied on biomarkers such as chroDebating a testosterone “sex gap”