A Beneficial Role of Rooibos in Diabetes Mellitus: A Systematic Review and Meta-Analysis

Abstract

In a rapid increase in cases of diabetes mellitus worldwide, there has been interested in the use of plant-derived polyphenols as nutraceuticals to prevent the onset and progression of diabetes mellitus and its associated complications. Aspalathus linearis, commonly known as rooibos, is a rich source of uncommon glycosylated plant polyphenols with various critical health-promoting properties, including the prevention and treatment of diabetes mellitus (DM). This study aimed to examine these effects by meta-analyzing the current evidence in diabetic rodent models. Peer-reviewed studies written in English from two databases, PubMed and Embase, were searched up to 28 February 2018. Studies reporting blood glucose levels in diabetic rodents with and without receiving rooibos extracts or their major phenolic compounds are included. Twelve studies enrolling 88 diabetic rodents treated with rooibos extracts or their polyphenols and 85 diabetic control males reported blood glucose levels. The pooled effect size was -0.89 (95% CI: -1.44 to -0.35) with a substantial heterogeneity (I² = 67.0%). This effect was likely to be modified by type of rooibos extracts and their polyphenols and treatment period. Blood glucose levels were significantly lower in diabetic rodent models treated with the phenolic compound rich in rooibos extracts, PPAG.

Keywords: blood glucose levels; diabetic rodent models; meta-analysis; rooibos extracts.

Figure 1

Flow diagram of literature search and selection process.

Figure 2

Flow diagram of literature search and selection process. Meta-analysis of Hedges’ g of blood glucose levels in DM rodents with and without treatment of rooibos extracts or associated major phenolic compounds. Summary estimates were analyzed using a random-effects model. CI, confidence interval.

Figure 3

Subgroup analysis for Hedges’ g of blood glucose levels in DM rodents treated with various types of rooibos extracts and major phenolic compounds or vehicles. Summary estimates were analyzed using a random-effects model. CI, confidence interval.

Figure 4

Meta-regression analysis for Hedges’ g of blood glucose levels and treatment period in DM rodents treated with or without rooibos extracts or major phenolic compounds. Summary estimates were analyzed using a random-effects model.

Figure 5

Funnel plots of standard error by Hedges’ g of blood glucose levels in DM rodents treated with or without rooibos extracts or major phenolic compounds. Open and closed diamond indicates the imputed summary estimates before and after Duval and Tweedie’s Trim and Fill adjustment (random-effects models), respectively. No imputed studies were found in re-displayed funnel plots by Duval and Tweedie’s Trim and Fill analysis.

Figure 6

Structures of major flavonoids in rooibos extracts [14] Z-2-(β-d-glucopyranosyloxy)-3-phenylpropenoic acid, PPAG.