Meta-Analysis: Effects of Zinc Supplementation Alone or with Multi-Nutrients, on Glucose Control and Lipid Levels in Patients with Type 2 Diabetes

Abstract

The present study aims to assess the effects of zinc supplementation on metabolic parameters in patients with type 2 diabetes. A literature search was conducted in PubMed^TM, Google Scholar^TM, and Scopus^TM up to March 2018. Twenty randomized controlled trials met the predefined inclusion criteria and were included in the meta-analysis. Weighted mean difference (WMD) with 95% confidence intervals (CIs) were calculated for net changes in glycemic indices including fasting blood glucose (FBG) and hemoglobin A1c (HbA1c), and in lipid markers including total cholesterol (TC), triglyceride (TG), low-density lipoprotein cholesterol (LDL-c), and high density lipoprotein cholesterol (HDL-c). Subgroup analyses were performed based on intervention and study quality. Compared to controls, zinc supplementation significantly reduced the concentrations of both FBG and HbA1c (FBG WMD: -19.66 mg/dL, 95% CI: -33.71, -5.62; HbA1c WMD: -0.43 mg/dL, 95% CI: -0.80, -0.07). The pooled estimate showed a significant decrease in serum TC and LDL-c, and increase in serum HDL-c levels in treatment group compared with the control group (TC WMD: -18.51 mg/dL, 95% CI: -21.36, -15.66; LDL-c WMD: -4.80 mg/dL, 95% CI: -6.07, -3.53; HDL-c WMD: 1.45 mg/dL, 95% CI: 1.40, 1.51). Subgroup analysis of "no co-supplement" intervention demonstrated significant differences for mean changes in HDL-c and FBG levels, whereas subgroup analysis of high quality studies showed significant differences for mean changes of LDL-c, HDL-c, and FBG levels. Results suggested that zinc supplementation reduces FBG, HbA1c and LDL-c levels and increases HDL-C levels; however, these changes were related to intervention and quality of studies.

Keywords: glycemic status; lipid profile; meta-analysis; type 2 diabetes; zinc supplementation.

Fig. 1

Flow diagram of included and excluded studies.

Fig. 2

Forest plots showing the association between zinc supplementation and the glycemic indices; (A) fasting blood glucose (FBG) and (B) hemoglobin A1c (HbA1c).

Fig. 3

Forest plots showing the association between zinc supplementation and serum lipid indices; (A) triglyceride (TG), (B) total cholesterol (TC), (C) low-density lipoprotein cholesterol (LDL-c), and (D) high-density lipoprotein cholesterol (HDL-c).

Fig. 3

Forest plots showing the association between zinc supplementation and serum lipid indices; (A) triglyceride (TG), (B) total cholesterol (TC), (C) low-density lipoprotein cholesterol (LDL-c), and (D) high-density lipoprotein cholesterol (HDL-c).

Fig. 4

Results of meta-analysis, Forest plot of point estimate effect sizes reported as Cohen’s d (X-axis) evaluating zinc supplementation on (A) fasting blood glucose (FBG), (B) hemoglobin A1c (HbA1c), (C) triglyceride (TG), (D) total cholesterol (TC), (E) low-density lipoprotein cholesterol (LDL-c), and (F) high-density lipoprotein cholesterol (HDL-c) using the random effects model. Points represent weighted effect size, lines represent 95% confidence intervals (CIs). Triangle indicates overall effect size and 95% CI.

Fig. 5

Funnel plot of studies included in the meta-analysis for the outcome of (A) low-density lipoprotein cholesterol (LDL-c) and (B) fasting blood glucose (FBG). MD, mean difference; SE, standard error.