Effects of zinc supplementation on serum adiponectin concentration and glycemic control in patients with type 2 diabetes

Background: Previous studies have suggested that zinc is involved in insulin homeostasis. Adiponectin is a well-known adipokine with anti-diabetic, anti-atherogenic, and anti-inflammatory properties. The aim of this study was to investigate the effect of zinc supplementation on glycemic control, and the potential mediating role of adiponectin, in patients with type 2 diabetes. Methods: In this randomized double-blind placebo-controlled clinical trial, 60 patients with diabetes, 30-60 years, were randomized to receive either 30 mg/d zinc (as zinc gluconate) or placebo for 12 weeks. Circulating levels of adiponectin, zinc, glucose homeostasis parameters, and lipid profiles, as well as anthropometric parameters and dietary intakes, were assessed. Results: About 53.3% of the patients had zinc insufficiency at baseline. Serum zinc levels improved significantly in the intervention than control group following 12 weeks supplementation (P < 0.001). Adiponectin (1.23 +/- 2.23 mu g/ml, P = 0.006) and insulin (3.6 +/- 4.66 mu IU/ml, P = 0.001) levels increased significantly compared to baseline in the zinc group; but this change was not significant compared with the control group. Following supplementation, there were no significant differences in glycemic control and anthropometric parameters between the two groups. Serum HDL levels increased significantly in the zinc (5.37 +/- 14.8 mg/dl) compared to control (-1.53 +/- 6.9 mg/dl) group following supplementation (P = 0.039). Conclusion: Despite a significant increase in serum zinc level, no improvement was observed in glycemic control, following 12 weeks supplementation with 30 mg/d zinc (as zinc gluconate). Zinc supplementation restored adiponectin concentrations partly within the intervention group, and increased HDL levels compared to the control group. The current findings did not support improvement in glucose homeostasis following zinc supplementation in patients with type 2 diabetes under the present study design.