Preliminary study of bone biomarkers in elite female ballet dancers

Elite female ballet dancers are at high-risk of bone stress injuries (BSI) due to high-levels of weight-bearing exercise causing micro-cracks to form in the bone. The consistently high volumes of weight-bearing exercise may lead to a low BMI which reduces oestrogen levels by suppressing the gonadotrophin axis. The combination of high-levels of weight-bearing exercise and low oestrogen may be associated with increased bone remodelling. Investigating the relationship between exercise, BMI, oestrogen, and bone remodelling is crucial for developing prevention and management strategies for BSI. We conducted a pilot study of 4 weeks in a group of elite female professional ballet dancers and in female controls: the study subjects were monitored for self-reported weekly exercise, BMI, urinary oestrogen metabolites (2OHE1 and 16OHE1) and urinary NTX, a marker of bone resorption and proxy for remodelling. Measurements were collected at baseline, week 2 and 4. Dancers exhibited significantly higher hours of exercise per week (p = 0.004), and a BMI significantly lower (p = 0.030) than that of age-matched controls. In contrast, the levels of oestrogen metabolites (p = 0.050) and NTX (p = 0.460) were comparable in the two groups. Using NTX as a biomarker of bone remodelling, these results suggest that despite intense weight-bearing exercise, ballet dancers may not undergo higher bone remodelling than controls. The resulting insufficiency of bone remodelling may increase the risk of BSI because micro-cracks might accumulate in the bone faster than damaged tissue could be replaced. Based on these findings, larger studies will be designed to assess the effect of bone remodelling on BSI risk and recovery in professional ballet dancers, to develop a platform of prevention and treatment strategies including screening programmes to identify dancers at risk.