Prevalence of and Traits Associated with Low BMD among Female Adolescent Runners

Purpose: Identify the prevalence of and traits that may increase the risk of low bone mineral density (BMD) among 93 female adolescent competitive endurance runners. Methods: Participants were 93 high school runners, ages 13-18 yr, from southern California. Eating attitudes and behaviors were assessed using the Eating Disorder Examination Questionnaire (EDE-Q). Menstrual and sports participation history were evaluated using an interviewer-assisted, self-report questionnaire. Bone mineral density (BMD) of the spine (L1-L4), total hip, and total body were measured by dual-energy x-ray absorptiometry. The -2 and -1 BMD age-matched, gender-specific z-score cutoffs were used to categorize girls as having low bone mass for age. Results: Among the female runners, 11.8% and 28% met the -2 and -1 BMD z-score cutoffs, respectively, whereas 25.8% reported menstrual irregularity (MI). Total hip BMD, lumbar spine BMD, and lumbar spine BMD z-score were significantly lower in runners with MI after adjusting for body mass index (BMI) and lean tissue mass. Runners that participated in five or more compared with three seasons of endurance running exhibited a significantly lower total body and lumbar spine BMD z-score after adjusting for BMI, lean tissue mass, and number of menstrual cycles in the past year. Multiple regression analysis indicated that MI, participation in five or more seasons of endurance running, BMI, and lean tissue mass were independent predictors of low BMD. Conclusion: Female adolescent endurance runners may represent a population with an increased risk of low bone mass. Future studies are necessary to further understand the factors contributing to low bone mass in young runners and to identify behavioral strategies that will promote optimal bone mineral accumulation during the adolescent years.