Changes in bone density and bone markers in rhythmic gymnasts and ballet dancers: implications for puberty and leptin levels

Abstract

OBJECTIVE: Our aim was to compare physical activity and biochemical markers with bone mineral acquisition in rhythmic gymnasts and ballet dancers. METHODS: Weight, height, body mass index, nutritional intake, bone age and menstrual histories were analyzed in nine rhythmic gymnasts, twelve ballet dancers and fourteen controls. Bone mineral density (BMD) was assessed by X-ray absorptiometry at the lumbar spine, hip and radius. Bone alkaline phosphatase (bAP) and amino-terminal propeptide of procollagen I (PNIP) in serum and urinary alpha-isomer of the carboxy-terminal telopeptide of collagen I (alpha-CTX) were measured. RESULTS: Bone age was delayed 2 years and mean age at menarche was 15+/-0.9 years in rhythmic gymnasts and 13.7+/-1 years in ballet dancers, compared with 12.5+/-1 years in controls. Trocanteric and femoral neck BMD was significantly higher in rhythmic gymnasts compared with ballet dancers and controls. Right forearm (non-loaded zone) BMD was significantly decreased in rhythmic gymnasts and ballet dancers compared with controls. All subjects had normal bAP and PNIP levels, but the alpha-CTX/creatinine (Cr) ratio was increased in rhythmic gymnasts (P<0.001) with an inverse correlation between right forearm BMD and the alpha-CTX/Cr ratio (r=-0.74, P<0.001). Serum leptin levels were decreased in rhythmic gymnasts and ballet dancers. Rhythmic gymnasts had a positive correlation between right forearm BMD and leptin levels (r=0.85, P<0.001). CONCLUSIONS: Decreased bone mass in rhythmic gymnasts could be partially explained by an increase in bone resorption. Serum leptin levels could be implicated in the pubertal delay and be a good marker of bone mass in these subjects.