Effects of zinc supplementation on diabetes mellitus: a systematic review and meta-analysis

The number of people with diabetes and pre-diabetes are exponentially increasing. Studies on humans have shown the beneficial effects of Zinc supplementation in patients with diabetes. The present study aims to systematically evaluate the literature and meta-analyze the effects of Zinc supplementation on diabetes. A systematic review of published studies reporting the effects of Zinc supplementations on diabetes mellitus was undertaken. The literature search was conducted in the following databases; PubMed, Web of Science and SciVerse Scopus. A meta-analysis of studies examining the effects of Zinc supplementation on clinical and biochemical parameters in patients with diabetes was performed. The total number of articles included in the present review is 25, which included 3 studies on type-1 diabetes and 22 studies on type-2 diabetes. There were 12 studies comparing the effects of Zinc supplementation on fasting blood glucose in patients with type-2 diabetes. The pooled mean difference in fasting blood glucose between Zinc supplemented and placebo groups was -18.13 mg/dl (95%CI:-33.85,-2.41; p < 0.05). 2-h post-prandial blood sugar also shows a similar distinct reduction in (-34.87 mg/dl [95%CI:-75.44; 5.69]) the Zinc treated group. The reduction in HbA1c was -0.54 % (95%CI:-0.86;-0.21) in the Zinc treated group. There were 8 studies comparing the effects of Zinc supplementation on lipid parameters in patients with type-2 diabetes. The pooled mean difference for total cholesterol between Zinc supplemented and placebo groups was -32.37 mg/dl (95%CI:-57.39,-7.35; p < 0.05). Low-density lipoprotein cholesterol also showed a similar distinct reduction in the Zinc treated group, the pooled mean difference from random effects analysis was -11.19 mg/dl (95%CI:-21.14,-1.25; p < 0.05). Studies have also shown a significant reduction in systolic and diastolic blood pressures after Zinc supplementation. This first comprehensive systematic review and meta-analysis on the effects of Zinc supplementation in patients with diabetes demonstrates that Zinc supplementation has beneficial effects on glycaemic control and promotes healthy lipid parameters. Further studies are required to identify the exact biological mechanisms responsible for these results.