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Submitted on March 11, 2004
Accepted on October 8, 2004
Dept. of Diabetes and Endocrinology, GKT School of Medicine, St. Thomas' Hospital, London SE1 7EH, UK; Aarhus University Hospital, DK-8000, Aarhus C, Denmark; Institute of Mathematics, Statistics and Actuarial Science, University of Kent, Canterbury, Kent, CT2 7NF, UK; Department of Endocrinology, Sahlgrenska University Hospital, SE-413 45 Gothenburg, Sweden; Department of Internal Medicine and Cardiovascular Sciences University Federico II, Napoli, Italy; Kolling Institute of Medical Research, University of Sydney, Royal North Shore Hospital, Sydney, NSW 2065, Australia
* To whom correspondence should be addressed.
James Gibney, E-mail: j.gibney{at}st-vincents.ie
There is a need to develop a test to detect growth hormone (GH) abuse by elite athletes. Measured levels of GH in blood or urine, however, provide little information on the GH-IGF-I axis. Previous studies have identified a series of indirect markers of GH action that are markedly altered by administration of GH but to a lesser degree by acute exercise. This study was undertaken to determine the physiological range of these GH-dependent variables in elite athletes following a competitive event, to determine whether such values differ from resting values in normal and athletic subjects, and to establish whether any adjustments to this range are required on the basis of age, gender, demographic characteristics or the nature of exercise performed.
Serum samples were collected from 813 elite athletes (537 males and 276 females; age range 17 - 64 yr) from 15 sporting disciplines within two hours of completion of a major competitive event. Insulin-like growth-factor-I (IGF-I), insulin-like growth-factor binding protein 2 (IGFBP-2), insulin-like growth-factor binding protein 3 (IGFBP-3), acid labile subunit (ALS) and the bone and soft tissue markers, osteocalcin, carboxy-terminal propeptide of type I procollagen (PICP), carboxy-terminal cross-linked telopeptide of type I collagen (ICTP) and procollagen type III (PIIIP) were measured. Sporting category, gender, age, height, weight, BMI and racial group of the athlete were documented, and results were compared both to normative data and to values obtained from elite athletes under resting conditions.
41% of IGF-I values in male and 41% of values in female athletes were above the upper limits of 99% reference ranges derived from resting values in a normal population. Post-competition levels of all variables except PICP and ICTP differed from resting values. There was a consistent age-dependent fall in measured levels of all variables (P < 0.0001) with the exception of IGFBP-2, which increased with age (P < 0.0001). BMI, but not height, exerted a small but significant influence on several variables. Following adjustment for age, there were no significant differences in levels of any of the measured variables between sporting categories. IGFBP-2 and IGFBP-3 were lower in 35 black athletes, when compared with 35 white athletes matched for age, gender, height, BMI and sporting category.
We have demonstrated that there are predictable age dependent levels of GH-dependent markers in elite athletes that are consistent even at the extremes of physical exertion and that these are independent of sporting category. Normative data applicable to white athletes is provided. This provides important groundwork for the development of a test for GH abuse, although these values may be specific for the reagents and assays used.
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