Sport Specialization and Low Bone Mineral Density in Female High School Distance Runners.

CONTEXT: Sport specialization may contribute to sport injury and menstrual dysfunction in female high school distance runners. Despite the recent growth in sport specialization, including among high school-aged runners, the association of sport specialization with bone mineral density (BMD) remains poorly described.

OBJECTIVE

To evaluate whether sport specialization was associated with BMD in female high school distance runners.

DESIGN

Cross-sectional study.

SETTING

Six high schools.

PATIENTS OR OTHER

PARTICIPANTS

Sixty-four female runners (age = 15.6 ± 1.4 years) who competed in cross-country or track distance events and were not currently on birth control medication.

MAIN OUTCOME MEASURE(S): Each runner completed a survey on menstrual history and sport participation. Height and weight were measured, and dual-energy x-ray absorptiometry was used to measure whole-body, spine, and hip BMD. Each runner was assigned a sport specialization status: low (participation in ≥1 nonrunning sport and distance-running sport(s) for ≤8 mo/y); moderate (participation in both distance-running sport(s) ≥9 mo/y and ≥1 nonrunning sport(s) or limited to distance-running sport(s) for ≤8 mo/y); or high (participation only in distance-running sport(s) for ≥9 mo/y). Multivariable logistic regression was performed to determine the adjusted odds ratio and 95% confidence interval for sport specialization to BMD values, adjusting for body mass index and gynecological age.

RESULTS

Overall, 21.9%, 37.5%, and 40.6% of participants were high, moderate, or low sport specializers, respectively. Low BMD (spine or whole-body BMD z score < -1.0 [standardized by age and sex normative values]) was present in 23 (35.9%) runners. Compared with low sport specializers, high sport specializers were 5 times more likely (adjusted odds ratio = 5.42, 95% confidence interval = 1.3, 23.3; P = .02) to have low BMD.

CONCLUSIONS

A high level of sport specialization in high school female distance runners may be associated with a heightened risk for low BMD. Further investigation of this association is warranted due to the health concerns about low BMD in adolescent female runners.