The assessment of bone metabolism in female elite endurance athletes by biochemical bone markers

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Purpose:Premature osteoporosis is a frequent problem in female athletes. Current concepts suggest that a disruption of the hypothalamic-pituitary axis leads to hypoestrogenism, which then causes amenorrhea and osteoporosis. However, the underlying mechanisms have been insufficiently investigated. Osteoprotegerin (OPG) and soluble TNF-α receptor antagonist ligand (sRANKL) regulate the balance of osteoblasts and osteoclasts. Their role in the pathogenesis of osteoporosis in female athletes has not been studied yet.Methods:We measured OPG and sRANKL in relation to biochemical bone markers [osteocalcin (OC), bone alkaline phosphatase (BAP), serum β-crosslaps (CTx)] and female sex hormones [estradiol (E2) and luteinizing hormone (LH)] in fastening blood samples from 25 female elite endurance athletes and 25 matched controls.Results:Athletes exhibited significantly higher levels of the bone resorption marker CTx than controls (0.61±0.26 vs. 0.44±0.15 ng/ml). OPG and sRANKL were not changed. Subgroup analysis revealed that athletes using oral contraceptives [A-OCC(−)] had significantly higher levels of CTx (0.82±0.20 vs. 0.50±0.14 ng/ml), BAP [37.3 (23.2-54.4) U/l vs. 25.2 (20.3-35.6) U/l] and OPG (3.4±0.8 vs. 2.7±0.8 ng/ml) than controls who did not use oral contraceptives [C-OCC(−)]. While the difference for CTx exceeded the least significant change in this marker by approximately 30%, the differences for the bone formation markers OC and BAP were close to the least significant change. In athletes using oral contraceptives [A-OCC(+)] we found no differences compared to controls.Conclusions:A-OCC( −) athletes have increased bone turnover with a particular stimulation of bone resorption. The increased bone resorption is not accompanied by a shift of the OPG/sRANKL relationship towards an osteoclastogenic constellation. Since increased bone resorption was not detectable in A-OCC(+) athletes, it can be suggested that OCC use might protect bone health in female athletes.

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