Prospective Evaluation of Vitamin D Levels and Stress Injury in Collegiate Female Long-Distance Runners

CATEGORY: Lesser Toes, Midfoot/Forefoot, Sports INTRODUCTION/PURPOSE: The incidence of stress injury in female runners is reported in up to 21% of competitive runners, with female runners at higher risk for stress injury than men. Bone metabolism is closely linked with vitamin D, which may play a role in the high prevalence of stress fractures in female runners. Although runners who train outdoors in the southeastern US have adequate vitamin D levels, no study to date has evaluated runners in northeastern US. The aim of the study was to prospectively evaluate the relationship between 25-OH vitamin D serum levels and the incidence of stress injury in a cohort of collegiate competitive long-distance runners. METHODS: 101 female collegiate runners from 7 Northeastern US colleges competing in varsity cross country were enrolled. Surveys were collected from all the study participants at the start of the fall cross country season reviewing demographics, weekly mileage, and medical history, including previous stress fracture incidence. Additionally, baseline (“summer”) serum 25-hydroxy vitamin D levels were obtained. Subjects insufficient in vitamin D (<30ng/mL) were supplemented with cholecalciferol (D3) 50,000 units weekly for 8 weeks and 2,000 units daily for an additional 1 month. In subjects with vitamin D insufficiency, repeat labs were performed at 3 months and repeat surveys distributed. To account for variation in season and geographical location, all subjects underwent repeat vitamin D labs at 6 months (”winter”). Fisher’s exact test was used to determine whether vitamin D levels were correlated with incidence of stress fracture. RESULTS: 91/101 (90%) subjects with mean BMI of 20.5 and average age of 20 years completed all study requirements. The mean summer and winter vitamin D serum levels were 64.0 ng/mL (SD 16.6; range 28.9-112.9) and 45.0 ng/mL (SD 13.8; range 20.1- 90.6), respectively. One subject (1%) in the summer and 9 subjects (10%) in the winter were supplemented for vitamin D insufficiency. 7/10 (70%) insufficient subjects and 28/81 (35%) vitamin D sufficient subjects reported a stress fracture during the study period. Patients that had an insufficient vitamin D result were significantly more likely to have a stress fracture during the study period (p=0.041; Table 1). The mean change in vitamin D level from summer to winter was -19.7 (SD 14.4; range -60.5- 60.7). CONCLUSION: The high rate of stress fractures in this cohort of collegiate female long-distance runners is greater than previously reported. Runners who are vitamin D insufficient are at a higher risk to incur a stress fracture. The results of the study also highlight the considerable seasonal variance in vitamin D levels amongst female collegiate long-distance runners in the northeastern US. Further study is needed to determine whether vitamin D supplementation reduces the risk of stress fractures.