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.

Low energy availability in exercising men is associated with reduced leptin and insulin but not with changes in other metabolic hormones

“…It is further possible that the endocrine suppression during low energy availability was blunted by increased circulating concentrations of binding proteins, which were not assessed in this study. Dolan et al reported that male jockeys, a group known to undergo repeated periods of energy deficiency, demonstrated normal total testosterone but elevated sex hormonebinding globulin concentrations, resulting in reduced testosterone bioavailability when compared to matched controls (Dolan et al, 2012). Future controlled experiments are needed to determine how the magnitude and duration of the energy deficit, basal leptin concentrations and changes in binding proteins modulate the suppression of metabolic hormones during energy deficiency.…”

“…Because men have to invest less energy for reproductive purposes than women (Bronson, 1985), it is not surprising that the male reproductive system appears more robust against energy deficiency. Other health-related outcomes of chronic energy deficiency, such as impaired bone health, have also been reported in exercising men (Campion et al, 2010;Dolan et al, 2012). However, the underlying mechanisms, the dose-response relationship with energy availability and the acute vs chronic nature of these effects remain Table 3.…”

“…These health effects have been reported primarily in exercising women and have been captured under the term female athlete triad (De Souza et al, 2014;Nattiv et al, 2007). However, observational studies suggest that male athletes, particularly those competing in sports that emphasize leanness or a low body weight, demonstrate an increased propensity for disordered eating (Martinsen, Bratland-Sanda, Eriksson, & Sundgot-Borgen, 2010;Rosendahl, Bormann, Aschenbrenner, Aschenbrenner, & Strauss, 2009) and that reproductive function and bone health may also be impaired in exercising men at risk of chronic energy deficiency (Campion et al, 2010;De Souza, Arce, Pescatello, Scherzer, & Luciano, 1994;Dolan et al, 2012;Hagmar, Berglund, Brismar, & Hirschberg, 2013).…”

Disordered Eating and Eating Disorders in Aquatic Sports

“…The prevalence of menstrual dysfunction and impaired bone health in female elite athletes competing in weight-sensitive sports is higher than that among female athletes representing sports that are less sensitive to the effects of body weight (Coelho et al, 2010;Rauh et al, 2010). In addition, it is evident that energy deficiency, suppressed hormonal activity, and reduced bone mineral density (BMD) also affect male athletes (Dolan et al, 2012;Hetland et al, 1993;Smathers et al, 2009). For example, Smathers et al (2009) found that 9% of male competitive cyclists and 3% of age-and body mass-matched control subjects were classified as osteoporotic, and as many as 25% of the cyclists had low BMD compared with 10% of the control subjects.…”

Association Between Energy Balance and Metabolic Hormone Suppression During Ultraendurance Exercise

“…14 It is well recognized in the literature that the suppression of metabolic hormones secondary to prolonged energy deficiency is associated with unfavorable health outcomes, such as impaired reproductive, bone, and cardiovascular health. [16][17][18][19] The suppression of testosterone and IGF-1, which both possess strong anabolic properties, may further result in unfavorable alterations in fuel utilization and more importantly, in the long-term loss of muscle mass and muscle function. 20,21 Therefore, it remains unclear whether strategies to increase dietary energy intake during prolonged ultra-endurance exercise in efforts to prevent energy deficiency could also attenuate the suppression of metabolic hormones, and minimize the detrimental effects of energy deficiency in the long-term.…”