Bone Abstracts

Objectives: By prospectively evaluating a cohort of girls we aim to identify population patterns linking adipokines and bone turnover during early and late adolescence and to assess the associations of those patterns with forearm bone mineral density (BMD).

Methods: The study was developed within a population-based cohort of urban adolescents born in 1990 and assembled in public and private schools of Porto, Portugal (EPITeen). We analysed prospective data from 300 girls evaluated at 13 and 17 years of age. Anthropometric assessment included height, weight and body fat percentage. BMD was measured at the distal forearm using dual-energy X-ray absorptiometry. Pubertal development status was estimated through menarche age. Serum concentrations of leptin, adiponectin, receptor activator of nuclear factor κB ligand (RANKL), osteoprotegerin (OPG), collagen type 1 cross-linked C-telopeptide (CTX), and procollagen I N-terminal propeptide (PINP) were determined using commercially available enzyme-linked immunosorbent assays. Exploratory factor analysis was used to identify patterns of associations between serum parameters at each age and to assess their maintenance between 13 and 17 years of age. Associations between factors at each age and BMD were estimated using linear regression coefficients (95% CIs), crude and adjusted for height, weight, and menarche age.

Results: We found that the same two factors at 13 and 17 years of age, named ‘factor leptin CTX RANKL’ and ‘factor PINP OPG’, accounted for more than 40% of the variability observed in the selected set of variables. ‘Leptin CTX RANKL’ factors were positively associated with leptin and negatively with CTX and RANKL at 13 and at 17 years of age. There were crude positive associations between these factors and BMD, (β=25.1 (18.8, 31.4) at 13 and β=9.6 (3.8, 15.3) at 17 years), that lost significance after adjustment. ‘Factor PINP OPG’ was directly correlated with PINP and inversely with OPG but not associated with BMD at 13 or 17 years of age.

Conclusion: By using an exploratory approach to population data, we identified an important pattern linking fat and bone in adolescent girls, involving systemic mediation by leptin and local mediation by RANKL, reflecting an effect on bone resorption.