Differences in female athlete triad risk factors between Japanese and American female runners: A comparative study

Background: Differences in female athlete triad risk factors between runners from Japan and the United States have not been explored. Objective: To compare the prevalence of Triad risk factors and Triad components between female Japanese and American distance runners. Design: Observational, cross-sectional. Setting: Two universities; one in the United States and one in Japan. Participants: A total of 77 female runners: 36 Japanese middle- and long-distance runners, and 41 American distance runners. Interventions: Not applicable. Main Outcome Measures: Triad components were energy deficiency, menstrual disturbances, and poor bone health. Triad risk factors were, respectively for each component: body mass index, serum total triiodothyronine, and history of diagnosed eating disorders; delayed menarche, history of menstrual irregularity, and current oligoamenorrhea; and bone mineral density and history of stress fractures. Prevalence was compared with chi-square and Fisher's exact tests. Group differences were assessed with t-tests and Mann–Whitney U tests. Data are mean difference (95% confidence interval [CI]). Results: Japanese runners had lower body weight (−4.15 [95% CI, −7.03.to −1.27] kg, p =.005) and percentage of body fat (−5.2 [95% CI, −6.9 to −3.5] %, p <.001) than American runners, with no differences in body mass index, serum total triiodothyronine, age of menarche, or menstrual cycle length (p >.05). Japanese runners had significantly lower bone mineral density at the lumbar spine (−0.195 [95% CI, −0.246 to −0.143] g/cm², p <.001), total hip (−0.115 [95% CI, −0.165 to −0.064] g/cm², p <.001), and femoral neck (−0.214 [95% CI, −0.260 to −0.167] g/cm², p <.001), but higher total hip Z-scores than the American runners (0.5 [95% CI, 0.1 to 1.0], p =.022). The prevalence of energy deficiency (56% vs. 32%, p =.035), history of stress fractures (50% vs. 17%, p =.003), and of runners experiencing all three Triad components (42% vs. 16%, p =.014) was higher in Japanese than American runners. No other differences in prevalence were observed. Conclusions: Japanese female runners may be at a higher Triad risk than American peers, given their higher prevalence of energy deficiency risk factors, history of stress fractures, and of athletes experiencing all Triad components.