secular trend in thinness prevalence for 26 years (1989 - 2014) among high school runners in japan

Background: female distance runners are predisposed to thinness for performance reasons and at greater risk for health-related consequences than the general population. objectives: the aim of the study was to evaluate the secular trends in thinness among competitive distance runners in japanese high schools with sex-specific comparison. methods: body mass index (bmi) were analysed in 9,881 female and 12,786 male runners participating in the annual national road relay races between 1989 and 2014 using the directory of a track and field magazine. the age-specific trends of these variables and the prevalence of thinness were tested by linear and logistic regression, respectively. results: although bmi declined significantly among both male and female runners (coefficients: boys, -0.033, -0.030, and -0.032; girls, -0.033, -0.034, and -0.034 [all p < 0.001] in 15.5-, 16.5-, and 17.5-year-olds, respectively), the prevalence of severely thin runners significantly increased only among girls (odds ratios for the yearly change = 1.05 and 1.06 [both p < 0.01] for 16.5- and 17.5-year-olds, respectively). only 0.13% of male runners were regarded as severely thin throughout the study period. conclusions: the results suggested that severely thin girl runners has steadily increased. surveys on the health consequences of extreme thinness are necessary for the female adolescent runners.