Female Distance Runners Display Altered Bone Remodeling In Fasted Blood And 24 Hour Urine Biomarkers

Abstract

An increase in underlying bone remodeling is associated with increased fracture risk. The International Osteoporosis Foundation recommend overnight fasted plasma C-terminal cross linked telopeptide type 1 collagen (CTX) and N-terminal propeptide of type 1 procollagen (P1NP) as bone turnover markers (BTM) of homeostatic bone remodeling. Reflected by an increase in plasma CTX, endurance exercise increases bone resorption acutely for a number of hours post-exercise. Female distance runners (FDR) engage in frequent weight-bearing endurance exercise that may alter homeostatic bone remodeling and fracture risk. PURPOSE: To compare bone remodeling in FDR and non-athletic controls (CON). METHODS: Daily 24 h urine samples and fasted morning blood samples were collected for 7 consecutive days of habitual activity in 7 FDR (training volume ≥ 60 km/week; mean ± SD age: 24.1 ± 4.6 y, height: 1.70 ± 0.05 m, mass: 58.5 ± 5.5 kg, fat %: 18 ± 4%) and 11 CON (≤3 h/week intentional vigorous physical activity; mean ± SD age: 23.9 ± 4.1 y, height: 1.67 ± 0.05 m, mass: 64.5 ± 4.4 kg, fat %: 33 ± 6%) who provided prior informed consent for a study which had ethical approval. Plasma CTX and P1NP was measured by automated immunoassay (Roche Diagnostics) and urinary N-terminal cross linked telopeptide type 1 collagen (NTX) by ELISA (Osteomark). Data were pooled and analyzed independent of participant. Data violated the assumption of normality and are reported as the median (IQR). Groups were compared by Mann-Whitney U test. RESULTS: Median CTX was 31.4% lower (0.393(0.147) vs 0.573(0.333) ng/ml; p<0.001; d=0.7) and P1NP was 14.5% lower (55.12(32.39) vs 64.43(16.73) ng/ml; p=0.012; d=0.5) in FDR compared to CON. In contrast, median 24 h NTX was 36.7% higher in FDR (434.2 (572.7) vs 317.6 (302.6) nM bone collagen equivalents; p=0.033; d=0.4) compared to CON. CONCLUSION: Lower overnight fasted CTX and P1NP are deemed devoid of influence exerted by previous exercise or food intake and may indicate an adaptive, regulatory effect of chronic exercise training on systemic (homeostatic) bone remodeling in FDR. By contrast, 24 h urine NTX captures total bone resorptive activity, including response to exercise and diet accrued during the previous 24 h and appear to confirm significantly greater net daily bone resorption in FDR compared to CON.