Meta-analysis of the effect of herbal supplement on glycemic control in type 2 diabetes

Ethnopharmacological relevance: A variety of herbs has been used in traditional medicine for the treatment of diabetes. However, evidence is limited regarding the efficacy of individual herbs for glycemic control. We performed a systematic review and meta-analysis to evaluate the effect of herbal supplement on glycemic control in type 2 diabetes. Materials and methods: Randomized controlled trials were identified through electronic searches (MEDLINE, EMBASE and Cochrane Central Register of Controlled Trials) up until February 2011, historical searches of relevant articles and personal contact with experts in the area. Studies were included in the meta-analysis if they were (1) randomized placebo-controlled trial of single herb aimed at assessing glycemic control in type 2 diabetes, (2) of at least 8 weeks duration, and (3) reporting HbA(1c). Treatment effect was estimated with mean difference in the final value of HbA(1c) and FBG between the treatment and the placebo groups. Results: Nine randomized, placebo-controlled trials (n = 487 patients) were identified. Ipomoea batatas, Silybum marianum and Trigonella foenum-graecum significantly improved glycemic control, whereas Cinnamomum cassia did not. The pooled mean differences in HbA(1c), were -0.30% (95% CI -0.04% to -0.57%; P = 0.02), -1.92%(95% CI -0.51% to -3.32%; P = 0.008), and -1.13%(95% CI -0.11% to -2.14%; P = 0.03), respectively, for Ipomoea batatas, Silybum marianum, and Trigonella foenum-graecum. The corresponding values for FBG were -10.20 mg/dL (95% CI -5.32 mg/dL to -15.08 mg/dL; P < 0.0001) and -38.05 mg/dL (95% CI -9.54 mg/dL to -66.57 mg/dL; P = 0.009), respectively, for Ipomoea batatas and Silybum marianum. Conclusions: The current evidence suggests that supplementation with Ipomoea batatas. Silybum marianum, and Trigonella foenum-graecum may improve glycemic control in type 2 diabetes. Such effect was not observed with Cinnamomum cassia. Given the limitations of the available studies and high heterogeneity of the study results for milk thistle and fenugreek, further high quality, large controlled trials using standardized preparation are warranted to better elucidate the effects of these herbs on glycemic control in type 2 diabetes patients. (C) 2011 Elsevier Ireland Ltd. All rights reserved.