Oral Contraceptives and Bone Health in Female Runners

Purpose: To identify risk factors for stress fracture among young female distancerunners. Methods: Participants were 127 competitive female distance runners, aged 18-26, who provided at least some follow-up data in a randomized trial among 150 runnersof the effects of oral contraceptives on bone health. After completing a baselinequestionnaire and undergoing bone densitometry, they were followed an average of 1.85years. Results: Eighteen participants had at least one stress fracture during follow-up.Baseline characteristics associated (p<0.10) in multivariate analysis with stress fractureoccurrence were one or more previous stress fractures (rate ratio [RR] [95% confidenceinterval] = 6.42 (1.80-22.87), lower whole-body bone mineral content (RR = 2.70 [1.26-5.88] per one standard deviation [293.2 grams] decrease), younger chronologic age (RR =1.42 [1.05-1.92] per one year decrease), lower dietary calcium intake (RR = 1.11 [0.98-1.25] per 100 mg decrease), and younger age at menarche (RR = 1.92 [1.15-3.23] per oneyear decrease). Although not statistically significant, a history of irregular menstrualperiods was also associated with increased risk (RR = 3.41 [0.69-16.91]). Training-related factors did not affect risk. Conclusion: The results of this and other studiesindicate that risk factors for stress fracture among young female runners include previousstress fractures, lower bone mass, and, although not statistically significant in this study,menstrual irregularity. More study is needed of the associations between stress fractureand age, calcium intake, and age at menarche. Given the importance of stress fractures torunners, identifying preventive measures is of high priority.