Endocrine Abstracts

Introduction: We have recently presented data demonstrating total body and regional bone mass relative to body size is reduced in obese children. Adipokines have been shown to play a role in bone metabolism. We hypothesised that

1) increased bone turnover would be associated with reduced bone mass

2) increased serum leptin would be associated with increased osteoclastogenic factors

3) reduced adiponectin would be associated with increased osteoclastogenic factors.

Methods: We recruited 103 children following ethics approval. Bone turnover was assessed by serum P1NP (formation) and urinary CTX (resorption). DXA was used to measure total body and lumbar bone mineral content (BMC) and density (BMD), and total body fat mass (FM). Skeletal maturity was assessed using TW3 bone age.

Serum was analysed for the adipokines leptin, adiponectin; the osteoclastogenic factors TNFα and RANK-L; the decoy receptor for RANK-L, osteoprotegerin (OPG); and dickkopf-1 (DKK-1) an inhibitor of bone formation acting through down-regulation of wnt-signalling through LRP5.

Results: After adjustment for height, weight and gender using multiple regression, FM was negatively related to total body BMC (P=0.05) and BMD (P=0.03) and lumbar BMC (P<0.0001) and BMD (P=0.04). Fat mass was positively related to P1NP (P=0.007) and CTX (P=0.004) i.e. increased bone turnover.

Following correction for TW3 bone age and gender, leptin (P<0.0001) and adiponectin (P=0.006) were positively and negatively related to FM respectively. Leptin was inversely related to osteoprotegerin (P=0.01). Adiponectin was inversely related to DKK-1 (P=0.04). TNFα was significantly associated with RANK-L (P=0.006) and DKK-1 (P=0.003).

Conclusions: We showed that in obese children increased bone turnover was associated with reduced total body and regional bone mass relative to body size. We also showed that in obese children there were alterations in osteokines favouring inhibition of osteoblastogenesis and supporting osteoclastogenesis.

Obese children are at risk for significant skeletal ill health.