Metabolic syndrome (MetS), affecting over a billion people globally, is a cluster of risk factors (abdominal obesity, high blood pressure, high fasting blood glucose, high triglycerides, and low HDL-C) increasing cardiovascular disease and type 2 diabetes risk. Taurine, a sulfur-containing amino acid found in various foods and tissues, plays crucial roles in osmoregulation, mitochondrial function, and antioxidant defense. Its potential to modulate lipid and glucose metabolism, and exert anti-inflammatory effects, suggests its possible benefit in MetS. However, inconsistencies in clinical outcomes regarding taurine's impact on MetS necessitate a systematic review and meta-analysis of RCTs to determine its effectiveness in modifying MetS-related parameters.

Existing literature demonstrates taurine's diverse health benefits but shows inconsistent results regarding its impact on MetS. Studies have suggested its potential to improve glycemic markers, lipid profiles, and exhibit anti-inflammatory actions. These actions are likely mediated through various mechanisms including modulation of lipid metabolism (bile salt conjugation), influence on glycemic control (reduced hepatic glucose production, inhibition of glucagon, increased insulin clearance), and anti-inflammatory effects through the renin-angiotensin system. The need for a comprehensive meta-analysis of RCTs stems from the existing inconsistencies and a desire to clarify taurine's role in MetS.

This meta-analysis followed PRISMA guidelines and was registered on Inplasy.com. Searches were conducted across Embase, PubMed, Web of Science, Cochrane CENTRAL, and ClinicalTrials.gov up to December 1, 2023, using keywords related to taurine and MetS. Included studies were RCTs using pure taurine supplementation with a comparative arm (placebo or other interventions), providing data on pre- and post-intervention MetS parameters. Excluded studies were non-RCTs, those with short follow-up periods (<24h), studies using herbal treatments with unclear active ingredients, studies lacking necessary data, and studies not focusing on relevant MetS outcomes. Methodological quality was assessed using the Cochrane risk of bias tool (RoB 2). Primary outcomes were changes in SBP, DBP, FBG, TG, and HDL-C. Secondary outcomes included body composition, lipid profiles, glycemic profiles, and adverse effects. Meta-analysis was performed using Comprehensive Meta-Analysis software, and meta-regression was used to explore dose-dependent relationships. Heterogeneity was assessed using I² statistics. Publication bias was evaluated using funnel plots and Egger's regression test.

The meta-analysis included 25 RCTs with 1024 participants. Daily taurine doses ranged from 0.5 g/day to 6 g/day, with follow-up periods from 5 to 365 days. Compared to controls, taurine supplementation significantly reduced SBP (WMD −3.999 mmHg, 95% CI = −7.293 to 0.706, p = 0.017), DBP (WMD −1.509 mmHg, 95% CI = −2.479 to −0.539, p = 0.002), FBG (WMD: −5.882 mg/dL, 95% CI: −10.747 to −1.018, p = 0.018), and TG (WMD: −18.315 mg/dL, 95% CI: −25.628 to −11.002, p < 0.001). However, no significant effect was observed on HDL-C (WMD: 0.644 mg/dl, 95% CI: −0.244 to 1.532, p = 0.155). Meta-regression revealed a dose-dependent reduction in DBP and FBG. Secondary outcomes showed significant reductions in total cholesterol (TC) and low-density lipoprotein cholesterol (LDL-C), as well as improvements in HbA1c, HOMA index, and fasting insulin. No significant adverse effects were reported.

The significant reductions in SBP, DBP, FBG, and TG observed with taurine supplementation suggest it may effectively mitigate several MetS risk factors. The dose-dependent effects highlight the importance of optimizing taurine dosage for maximal benefit. The hypotensive effect may be due to increased nitric oxide and hydrogen sulfide production, while the improvement in glycemic control may be related to reduced hepatic glucose production, inhibition of glucagon, and enhanced insulin clearance. The reduction in TG levels could be attributed to increased bile acid production and LDL-C clearance. Although HDL-C was not significantly increased, trends suggest potential benefits. This study's findings contrast with some prior meta-analyses, potentially due to differences in study inclusion criteria and populations. The inclusion of a wider range of participant conditions and varying diabetes status could contribute to the observed effects. The lack of significant effects on body weight or BMI suggests that other lifestyle interventions may play a more crucial role in weight management.

This meta-analysis provides strong evidence supporting the beneficial effects of taurine supplementation on multiple MetS-related parameters. Taurine appears to be a safe and effective complementary therapeutic agent for MetS management. Further research is needed to determine optimal dosages, treatment durations, and long-term effects in various MetS subpopulations, particularly with an eye toward integrating taurine supplementation with existing pharmacological interventions to enhance treatment outcomes.

The observed heterogeneity across studies, potentially influenced by variations in participant characteristics, study protocols, and concurrent medication use, could have affected the statistical significance of some findings. The absence of direct waist circumference data and the limited duration of many included studies are further limitations. The differing study populations and medications (diuretics, ACE inhibitors) used in the included trials may have influenced the observed results on lipid profiles. Future studies should focus on larger, longer-term trials with standardized protocols and consistent participant characteristics to further validate these findings.