Effect of a long-term oral l-arginine supplementation on glucose metabolism: a randomized, double-blind, placebo-controlled trial

"Aim: This study assessed the efficacy of long-term l-arginine (l-arg) therapy in preventing or delaying type 2 diabetes mellitus. Methods: A mono-centre, randomized, double-blind, parallel-group, placebo-controlled, phase III trial (l-arg trial) was conducted on 144 individuals affected by impaired glucose tolerance (IGT) and metabolic syndrome (MS). l-Arg\/placebo was administered (6.4 g\/day) on a background structured lifestyle intervention for 18 months plus a 12-month extended follow-up period after study drug termination. Fasting glucose levels and glucose tolerance after oral glucose tolerance test were evaluated throughout the study. Results: After 18 months, l-arg as compared with placebo did not reduce the cumulative incidence of diabetes [21.4 and 20.8%, respectively, hazard ratio (HR), 1.04; 95% confidence interval (CI), 0.58-1.86] while the cumulative probability to become normal glucose tolerant (NGT) increased (42.4 and 22.1%, respectively, HR, 2.60; 95% CI, 1.51-4.46, p < 0.001). The higher cumulative probability to become of NGT was maintained during the extended period in subjects previously treated with l-arg (HR, 3.21; 95% CI, 1.87-5.51; p < 0.001). At the end of the extended period, the cumulative incidence of diabetes in subjects previously treated with l-arg was reduced as compared with placebo (27.2 and 47.1%, respectively, HR, 0.42; 95% CI, 0.24-0.75, p < 0.05). During both periods, l-arg significantly improved insulin sensitivity and β-cell function. Conclusion: Among persons with IGT and MS, the supplementation of l-arg for 18 months does not significantly reduce the incidence of diabetes but does significantly increase regression to NGT."