Bone Turnover Is Suppressed in Insulin Resistance, Independent of Adiposity

Context: The contribution of insulin resistance vs adiposity to bone mineral density (BMD), bone turnover, and fractures in humans remains unclear. Objective: To evaluate BMD and bone turnover markers (BTMs) in lean (n = 18) and overweight/obese individuals with (n = 17) and without (n = 34, insulin-sensitive [Ob(sensitive), n=15] or insulin-resistant [Ob(resistant), n=19] by homeostasis model assessment insulin resistance) diabetes mellitus. Design: Observational study. Outcome measures: Insulin sensitivity was assessed using the hyperinsulinemic-euglycemic clamp; whole body BMD and fat mass (FM) using dual energy X-ray absorptiometry; and by measurement of BTMs [osteocalcin (OC), procollagen type 1 N-terminal propeptide (P1NP), and collagen type 1 crosslinked C-terminal telopeptide (CTx)], with the patient fasting and during clamp hyperinsulinemia. Results: Fasting BTMs correlated with glucose infusion rate/fat-free mass (GIR/FFM) and adiponectin and, inversely, with fasting insulin and visceral fat (P <= 0.04 for all). Ob(sensitive), Ob(resistant), and diabetic individuals were matched by their FM percentage. Clamp GIR/FFM was similar in the lean and Ob(sensitive) subjects (P = 1) and approximately twofold greater (P, 0.001) than in the Ob(resistant) and diabetic subjects. BMD was greater in Ob(resistant) than in Ob(sensitive) (P = 0.04) and lean (P = 0.001) subjects. At baseline, compared with Ob(sensitive) and lean subjects, Obresistant and diabetic individuals had lower OC, P1NP, and CTx levels. This reached statistical significance for Ob(resistant) vs lean and Ob(resistant) vs Ob(sensitive) for both OC and CTx and for diabetic vs lean for CTx (P <= 0.04 for all). During hyperinsulinemia, lean individuals suppressed CTx more than did diabetic individuals (P = 0.03). On multiple regression analysis, visceral adiposity explained 16.7% and 19.3% of the baseline OC and CTx variability, respectively. Conclusions: Increased visceral adiposity and higher fasting insulin in insulin-resistant states are associated with lower fasting OC and CTx and failure to further suppress with more insulin.