Influence
of demographic factors and sport type on growth hormone-responsive markers
in elite athletes.
Nelson AE, Howe CJ, Nguyen TV, Leung KC, Trout
GJ, Seibel MJ, Baxter RC, Handelsman DJ, Kazlauskas R, Ho KK.
Endocrinol Metab. 2006 Nov; 91(11): 4424-32. Epub 2006
Aug 15.
CONTEXT: GH-responsive
markers of the IGF system and of collagen turnover hold promise as the
basis of a GH doping test.
OBJECTIVE: The purpose of
this study was to determine the influence of age, gender, body mass index
(BMI), ethnicity, and sporting type on GH-responsive serum markers in
a large cohort of elite athletes from different ethnic backgrounds.
DESIGN: The study was designed
as a cross-sectional study. Participants: A total of 1103 elite athletes
(699 males, 404 females), aged 22.2 +/- 5.2 yr, from 12 countries and
10 major sporting categories participated in this study.
MAIN OUTCOME MEASURES: Serum
IGF-I, IGF binding protein-3 (IGFBP-3), acid labile subunit (ALS), and
collagen markers [N-terminal propeptide of type I procollagen (PINP),
C-terminal telopeptide of type I collagen (ICTP), N-terminal propeptide
of type III procollagen (PIIINP)] were measured.
RESULTS: There was a significant
negative correlation (r = -0.14 to -0.58, P < 0.0005) between age and
each of the GH-responsive markers. Serum IGF-I, IGFBP-3, and ALS were
all lower (P < 0.05), whereas the collagen markers PINP, ICTP, and
PIIINP were higher (P < 0.05) in men than in women. Multiple regression
analysis indicated that age, gender, BMI, and ethnicity accounted for
23-54% of total between-subject variability of the markers. Age and gender
cumulatively accounted for 91% of the attributable variation of IGF-I
and more than 80% for PINP, ICTP, and PIIINP. Gender exerted the greatest
effect on ALS (48%), and BMI accounted for less than 12% attributable
variation for all markers. The influence of ethnicity was greatest for
IGFBP-3 and ALS; however, for the other markers, it accounted for less
than 6% attributable variation. Analysis of 995 athletes indicated that
sporting type contributed 5-19% of attributable variation.
CONCLUSIONS: Age and gender
were major determinants of variability of GH-responsive markers except
for IGFBP-3 and ALS. Ethnicity is unlikely to confound the validity of
a GH doping test based on IGF-I and these collagen markers.
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