title: An altered hormonal profile and elevated rate of bone loss are associated with low bone mass in professional horse-racing jockeys.
abstract: Horse-racing jockeys are a group of weight-restricted athletes, who have been suggested as undertaking rapid and extreme weight cycling practices in order to comply with stipulated body-mass standards. The aim of this study was to examine bone mass, turnover and endocrine function in jockeys and to compare this group with age, gender and body mass index matched controls. Twenty male professional jockeys and 20 healthy male controls participated. Dual energy X-ray absorptiometry scans and early morning fasting blood and urine samples were used to measure bone mass, turnover and a hormonal profile. Total body bone mineral density (BMD) was significantly lower in jockeys (1.143 ± 0.05 vs. 1.27 ± 0.06 g cm(-3), p < 0.01). Bone resorptive activity was elevated in the jockey group as indicated by significantly higher urinary NTx/creatinine (76.94 ± 29.52 vs. 55.9 ± 13.9 nmol mmol(-1), p < 0.01), resulting in a significantly negative uncoupling index between bone resorption and formation. Sex hormone binding globulin (SHBG) levels were significantly higher in jockeys (41.21 ± 9.77 vs. 28.24 ± 9.98 nmol L(-1), p < 0.01) with a lower percentage of bioavailable testosterone (48.89 ± 7.38 vs. 59.18 ± 6.74 %, p < 0.01). SHBG and insulin-like growth factor-1 were independent predictors of total body and femoral neck BMD, respectively (p < 0.05). In conclusion, it appears that professional jockeys have an elevated rate of bone loss and reduced bone mass that appears to be associated with disrupted hormonal activity. It is likely that this may have occurred in response to the chronic weight cycling habitually experienced by this group.
authors.affiliation: School of Health Sciences, Robert Gordon University, Garthdee Road, Aberdeen, AB10 7QG, Scotland, UK. e.dolan@rgu.ac.uk
authors.forename: Eimear
authors.initials: E
authors.lastname: Dolan
authors.forename: Adrian
authors.initials: A
authors.lastname: McGoldrick
authors.forename: Colin
authors.initials: C
authors.lastname: Davenport
authors.forename: Grainne
authors.initials: G
authors.lastname: Kelleher
authors.forename: Brendan
authors.initials: B
authors.lastname: Byrne
authors.forename: William
authors.initials: W
authors.lastname: Tormey
authors.forename: Diarmuid
authors.initials: D
authors.lastname: Smith
authors.forename: Giles D
authors.initials: GD
authors.lastname: Warrington
mesh_terms: D015502:Absorptiometry, Photon / Q000379:methods; D000328:Adult; D000818:Animals; D056352:Athletes; D001823:Body Composition / Q000502:physiology; D015992:Body Mass Index; D015519:Bone Density / Q000502:physiology*; D001862:Bone Resorption / Q000097:blood / Q000378:metabolism* / Q000473:pathology / Q000652:urine; D003404:Creatinine / Q000652:urine; D005272:Femur Neck / Q000378:metabolism / Q000473:pathology; D006728:Hormones / Q000378:metabolism*; D006736:Horses; D006801:Humans; D007334:Insulin-Like Growth Factor I / Q000378:metabolism; D008297:Male; D010012:Osteogenesis / Q000502:physiology; D012738:Sex Hormone-Binding Globulin / Q000378:metabolism; D013177:Sports; D013739:Testosterone / Q000097:blood; D055815:Young Adult
chemical_list: D006728:Hormones; D012738:Sex Hormone-Binding Globulin; D013739:Testosterone; D007334:Insulin-Like Growth Factor I; D003404:Creatinine