Bone Mineral Content as a Driver of Energy Expenditure in Prepubertal and Early Pubertal Boys

Abstract

Objective: To examine the associations of bone and bone-secreted factors with measures of energy metabolism in prepubertal and early pubertal boys.

Study design: Participants in this cross-sectional, observational study included 37 (69% black, 31% white) boys, aged 7-12 years (Tanner stage <III). Dual-energy X-ray absorptiometry was used to measure bone mineral content (BMC) and percent body fat. Indirect calorimetry was used to assess resting energy expenditure (REE). Fasting blood levels of osteocalcin (OCN), fibroblast growth factor 23 (FGF23), insulin, glucose, precursor product of type I collagen (N-terminal pro-peptide) and type I collagen, and C-terminal cross-linked telopeptide were measured. Pearson correlations were performed to evaluate relationships among BMC, OCN, FGF23, fasting insulin and glucose, and REE. Multiple linear regression models were used to test associations between OCN and BMC (independent variables) with fasting insulin and glucose and with REE, adjusting for bone turnover markers and further adjusted for percent body fat.

Results: BMC was correlated with REE and insulin. OCN was correlated with glucose in blacks only (r = 0.45, P < .05). FGF23 was not correlated with any markers of energy metabolism. BMC was associated with insulin level in blacks (β = 0.95, P = .001), which was attenuated by percent body fat (β = 0.47, P = .081). BMC was associated with REE in whites (β = 0.496.7, P < .05) and blacks (β = 619.5, P < .0001); but accounting for percent body fat attenuated the association in whites (β = 413.2, P = .078).

Conclusion: Our findings suggest that BMC is a determinant of fasting insulin and REE, and that the contribution of body fat appears to be race-specific. Endocrine effects of FGF23 and OCN on energy metabolism were not apparent.

Trial registration: Registered with ClinicalTrials.gov: NCT02040740, NCT02040727, and NCT01410643.