Zinc and glycemic control: A meta-analysis of randomised placebo controlled supplementation trials in humans

Background: Impaired zinc metabolism is prominent in chronic disorders including cardiovascular disease and diabetes. Zinc has the potential to affect glucose homeostasis in animals and humans and hence impact the risk of type 2 diabetes mellitus. Methods: A systematic review and meta-analysis of randomised placebo controlled trials was conducted to determine the effect of zinc supplementation on fasting blood glucose, HbA1c, serum insulin and serum zinc concentrations. Relevant studies for inclusion were identified from a literature search of electronic databases up to July 2011. Results: Fourteen reports (n=3978 subjects) were included in the meta-analysis. In the overall analysis, a small but statistically significant reduction in fasting glucose concentrations was observed (-0.19 ± 0.08. mmol/L, P=0.013) after zinc supplementation. HbA1c tended to decrease in zinc-supplemented individuals (-0.64 ± 0.36%, P=0.072). No significant effect was observed for serum insulin concentrations. Plasma zinc concentrations increased significantly following supplementation (+4.03 ± 0.81μmol/L, P=0.001). In secondary analyses of participants with chronic metabolic disease (types 1 and 2 diabetes mellitus, metabolic syndrome and obesity), zinc supplementation produced a greater reduction in glucose concentrations (-0.49 ± 0.11. mmol/L, P=0.001) compared to the effect that was observed in healthy participants. Conclusion: The significant albeit modest reduction in glucose concentrations and tendency for a decrease in HbA1c following zinc supplementation suggest that zinc may contribute to the management of hyperglycemia in individuals with chronic metabolic disease.