Plain language summary
Many studies have shown that type 2 diabetes is associated with increased formation of free radicals and decreased antioxidant potential, leading to oxidative damage of cell components. Increased formation of free radicals and decreased antioxidant potential, coupled with lipid abnormalities, are substantial risk factors for developing complications, especially microvascular ones. The aim of this study was to investigate the effect of oral supplementation of alpha-lipoic acid (ALA) on cardiometabolic risk factors in patients with type 2 diabetes. This study is a systematic review and dose–response meta-analysis of 16 randomised controlled trials with a total of 1035 patients with type 2 diabetes. Results show that: - each 500 mg/day oral ALA supplementation reduced haemoglobin A1c and body weight but did not affect low-density lipoprotein cholesterol concentration. - ALA supplementation reduced c-reactive protein, fasting plasma glucose, serum triglycerides, and diastolic blood pressure but it had no affect on serum total cholesterol and high-density lipoprotein cholesterol concentrations and systolic blood pressure. Authors conclude that their findings do not support ALA supplementation in clinical practice for patients with type 2 diabetes.
Abstract
OBJECTIVE To examine the dose-dependent influence of oral alpha-lipoic acid (ALA) supplementation on cardiometabolic risk factors in patients with type 2 diabetes (T2D). DESIGN We followed the instructions outlined in the Cochrane Handbook for Systematic Reviews of Interventions and the Grading of Recommendations, Assessment, Development, and Evaluation Handbook to conduct our systematic review. The protocol of the study was registered in PROSPERO (CRD42021260587). METHOD We searched PubMed, Scopus, and Web of Science to May 2021 for trials of oral ALA supplementation in adults with T2D. The primary outcomes were HbA1c, weight loss, and LDL cholesterol (LDL-C). Secondary outcomes included fasting plasma glucose (FPG), triglyceride (TG), C-reactive protein (CRP), and blood pressure. We conducted a random-effects dose-response meta-analysis to calculate the mean difference (MD) and 95% CI for each 500 mg/day oral ALA supplementation. We performed a nonlinear dose-response meta-analysis using a restricted cubic spline. RESULTS We included 16 trials with 1035 patients. Each 500 mg/day increase in oral ALA supplementation significantly reduced HbA1c, body weight, CRP, FPG, and TG. Dose-response meta-analyses indicated a linear decrement in body weight at ALA supplementation of more than 600 mg/day (MD600 mg/day: -0.30 kg, 95% CI: -0.04, -0.57). A relatively J-shaped effect was seen for HbA1c (MD: -0.32%, 95% CI: -0.45, -0.18). Levels of FPG and LDL-C decreased up to 600 mg/day ALA intake. The point estimates were below minimal clinically important difference thresholds for all outcomes. CONCLUSION Despite significant improvements, the effects of oral ALA supplementation on cardiometabolic risk factors in patients with T2D were not clinically important.
Methodological quality
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