Identifying Sex-Specific Risk Factors for Low Bone Mineral Density in Adolescent Runners

Background: Adolescent runners may be at risk for low bone mineral density (BMD) associated with sports participation. Few prior investigations have evaluated bone health in young runners, particularly males. Purpose: To characterize sex-specific risk factors for low BMD in adolescent runners. Study Design: Cross-sectional study; Level of evidence, 3. Methods: Training characteristics, fracture history, eating behaviors and attitudes, and menstrual history were measured using online questionnaires. A food frequency questionnaire was used to identify dietary patterns and measure calcium intake. Runners (female: n = 94, male: n = 42) completed dual-energy x-ray absorptiometry (DXA) to measure lumbar spine (LS) and total body less head (TBLH) BMD and body composition values, including android-to-gynoid (A:G) fat mass ratio. The BMD was standardized to Z-scores using age, sex, and race/ethnicity reference values. Questionnaire values were combined with DXA values to determine risk factors associated with differences in BMD Z-scores in LS and TBLH and low bone mass (defined as BMD Z-score -1). Results: In multivariable analyses, risk factors for lower LS BMD Z-scores in girls included lower A:G ratio, being shorter, and the combination of (interaction between) current menstrual irregularity and a history of fracture (all P < .01). Later age of menarche, lower A:G ratio, lower lean mass, and drinking less milk were associated with lower TBLH BMD Z-scores (P < .01). In boys, lower body mass index (BMI) Z-scores and the belief that being thinner improves performance were associated with lower LS and TBLH BMD Z-scores (all P < .05); lower A:G ratio was additionally associated with lower TBLH Z-scores (P < .01). Thirteen girls (14%) and 9 boys (21%) had low bone mass. Girls with a BMI 17.5 kg/m(2) or both menstrual irregularity and a history of fracture were significantly more likely to have low bone mass. Boys with a BMI 17.5 kg/m(2) and belief that thinness improves performance were significantly more likely to have low bone mass. Conclusion: This study identified sex-specific risk factors for impaired bone mass in adolescent runners. These risk factors can be helpful to guide sports medicine professionals in evaluation and management of young runners at risk for impaired bone health.