Objective: Osteocalcin (OC) might play a hormone-like role in energy metabolism and the regulatory circuit between the pancreas and osteoblasts. Effects of a 75-g oral glucose tolerance test (OGTT) on total OC, undercarboxylated (ucOC), and carboxylated osteocalcin (cOC) in insulin-resistant (IR) and noninsulin-resistant (nIR) premenopausal women was evaluated, and the relationships of changes in OC, ucOC, and cOC with area under the curve (AUC) insulin and the Matsuda index were examined.
Methods: In this cross-sectional study, 105 premenopausal women underwent OGTT; 18 were IR (homeostatic model assessment of insulin resistance [HOMA-IR] > 2.6; (2 with type 2 diabetes, 2 with impaired glucose tolerance), and 87 were nIR (3 with impaired glucose tolerance). Changes in total OC, ucOC, and cOC were evaluated 60 and 120 minutes after glucose loading.
Results: At baseline, IR subjects had significantly lower levels of total OC, cOC, and ucOC. In nIR women, total OC decreased by 19% from 18.0 ng/mL (14.5-24.7) at baseline to 14.6 ng/mL (10.9-17.8) after 120 minutes, ucOC decreased by 22% from 3.2 ng/mL (2.1-4.5) to 2.5 ng/mL (1.7-3.5), and cOC decreased by 26% from 14.9 ng/mL (12.1-20.4) to 11.1 ng/mL (9.0-14.5) (P < .001, respectively). No significant decreases were noted in IR subjects. The declines in OC and cOC predicted AUCinsulin (ΔOC: β = 0.301, P = .001; ΔcOC: β = 0.315, P < .001) and the Matsuda index (ΔOC: β = -0.235, P = .003; ΔcOC: β = -0.245, P = .002).
Conclusions: Glucose intake lowers levels of OC, ucOC, and cOC in nIR women, the extent of which predicts IR and insulin sensitivity in premenopausal women. OC parameters seem suppressed in IR women. There might be a differential osteoblast response to oral glucose in IR and nIR women, with OC reflecting this finding.