Bone resorption and incretin hormones following glucose ingestion in healthy emerging adults

BACKGROUND: Studies in adults indicate that macronutrient ingestion yields an acute anti-resorptive effect on bone, reflected by decreases in C-terminal telopeptide (CTX), a biomarker of bone resorption, and that gut-derived incretin hormones, glucose-dependent insulinotropic polypeptide (GIP) and glucagon-like peptide-1 (GLP-1), facilitate this response. There remain knowledge gaps relating to other biomarkers of bone turnover, and whether gut-bone cross-talk is operative during the years surrounding peak bone strength attainment. This study first, describes changes in bone resorption during oral glucose tolerance testing (OGTT), and second, tests relationships between changes in incretins and bone biomarkers during OGTT and bone micro-structure. METHODS: We conducted a cross-sectional study in 10 healthy emerging adults ages 18–25 years. During a multi-sample 2-hour 75 g OGTT, glucose, insulin, GIP, GLP-1, CTX, bone-specific alkaline phosphatase (BSAP), osteocalcin, osteoprotegerin (OPG), receptor activator of nuclear factor kappa-β ligand (RANKL), sclerostin, and parathyroid hormone (PTH) were assayed at mins 0, 30, 60, and 120. Incremental areas under the curve (iAUC) were computed from mins 0–30 and mins 0–120. Tibia bone micro-structure was assessed using second generation high resolution peripheral quantitative computed tomography. RESULTS: During OGTT, glucose, insulin, GIP, and GLP-1 increased significantly. CTX at min 30, 60, and 120 was significantly lower than min 0, with a maximum decrease of about 53 % by min 120. Glucose-iAUC(0-30) inversely correlated with CTX-iAUC(0-120) (rho = -0.91, P < 0.001), and GLP-1-iAUC(0-30) positively correlated with BSAP-iAUC(0-120) (rho = 0.83, P = 0.005), RANKL-iAUC(0-120) (rho = 0.86, P = 0.007), and cortical volumetric bone mineral density (rho = 0.93, P < 0.001). CONCLUSIONS: Glucose ingestion yields an anti-resorptive effect on bone metabolism during the years surrounding peak bone strength. Cross-talk between the gut and bone during this pivotal life stage requires further attention.