Study selection

Our initial search yielded 2517 publications. After removing duplicates and screening titles and abstracts, we deemed 2476 articles irrelevant and discarded them. We then conducted a full-text review of the remaining 41 studies.

Thirteen articles were excluded for various reasons (Table S3): four weren’t RCTs, one used an herbal treatment with unverified active compounds, one was a poster abstract lacking data, six did not report outcomes aligned with our research focus, and one only administered a single dose of the intervention. This resulted in the inclusion of 25 studies [7, 8, 17,18,19,20,21,22,23,24,25,26,27,28,29,30,31,32,33,34,35,36,37,38,39] in our final quantitative analysis (Fig. 1). Data extraction details for these RCTs are presented in Tables 1 and 2.

Fig. 1

The PRISMA flow diagram of the screening and review process.

Table 1 Summary of trials retrieved to investigate the impact of taurine on metabolic syndrome.Table 2 Summary of taurine interventions administered in the treatment arms of the trials.Study characteristic

Key features of the 25 RCTs, involving 1,024 participants, are summarized in Table 1. Conducted between 1983 and 2021 in diverse locations (Russia, Iran, Japan, Spain, Brazil, Canada, Ireland, China, Austria, Iraq, Denmark, the USA, and Egypt), the studies enrolled participants aged 8–113 years with a wide range of conditions. These included healthy individuals, post-surgical patients, and individuals with conditions such as heart failure, hypertension, coronary heart disease, heart valve defects, cardiomyopathy, type 1 diabetes mellitus, type 2 diabetes mellitus, obesity, alcoholism, and homocystinuria.

Quality assessment

Eighteen studies [8, 17,18,19,20,21,22,23,24,25, 27, 28, 30, 33,34,35,36,37,38] lacked information on allocation concealment, putting them at risk of bias. The remaining seven studies [7, 26, 29, 31, 32, 35, 39] had a low risk of bias, and none had a high risk of bias (Fig. S1, Table 3).

Table 3 Detailed quality assessment of the included studies using Cochrane risk of bias 2 tool.Primary outcomesEffects of taurine on SBP/DBP

Taurine supplementation significantly reduced SBP compared to the control group (WMD = −3.999 mmHg, 95% CI = −7.293 to −0.706, p = 0.017, I2 = 84.949) (Fig. 2a). This effect remained consistent even after excluding individual studies on the sensitivity analysis (Fig. S2a). Meta-analysis regression did not reveal a statistically significant linear relationship between total dose and SBP (coefficient = −0.024 mmHg per g, p = 0.113) (Fig. S3a), and a significant relationship between daily dose and SBP (coefficient = −1.1258 mmHg per g/day, p = 0.0055) (Fig. S4a).

Fig. 2

Forest plot of overall effects of taurine on systolic blood pressure (SBP) and diastolic blood pressure (DBP).

Taurine significantly reduced DBP levels (WMD = −1.509 mmHg, 95% CI = −2.479 to −0.539, p = 0.002, I2 = 14.077) (Fig. 2b). Similar to SBP, this DBP reduction persisted in the sensitivity analysis (Fig. S2b). Moreover, meta-regression analysis showed a significant correlation between total dose and decreased DBP (coefficient = −0.014 mmHg per g, p = 0.026) (Fig. S3b), and a significant relationship between daily dose and DBP (coefficient = −0.3247 mmHg per g/day, p = 0.0182) (Fig. S4b).

Effects of taurine on FBG

Overall, taurine supplementation significantly reduced FBG levels compared to the control group (WMD: −5.882 mg/dL, 95% CI: −10.747 to −1.018, p = 0.018, I2 = 75.457) (Fig. 3). This effect remained consistent even after excluding individual studies in the sensitivity analysis (Fig. S5). Interestingly, meta-regression revealed a significant correlation between total dose and decreased FBG levels (coefficient = −0.495 mg/dL per g, p = 0.0011) (Fig. S6), but no significant relationship between daily dose and FBG (coefficient = −1.5146 mg/dL per g/day, p = 0.0703) (Fig. S7).

Fig. 3

Forest plot of overall effects of taurine on fasting blood glucose (FBG).

Effects of taurine on TG

Taurine supplementation significantly reduced TG levels compared to the control group (WMD: −18.315 mg/dL, 95% CI: −25.628 to −11.002, p < 0.001, I2 = 35.539) (Fig. 4). This effect remained consistent even after excluding individual studies in a sensitivity analysis (Fig. S8). While meta-regression did not reveal a statistically significant dose-dependent relationship between total dose and TG reduction (coefficient = −0.0522 mg/dL per g, p = 0.0730) (Fig. S9), it revealed a significant relationship between daily dose and TG (coefficient = −3.3600 mg/dL per g/day, p = 0.0062) (Fig. S10).

Fig. 4

Forest plot of overall effects of taurine on triglyceride (TG).

Effects of taurine on HDL-C

Overall, taurine supplementation did not significantly increase HDL-C levels compared to the control group (WMD: 0.644 mg/dL, 95% CI: −0.244 to 1.532, p = 0.155, I2 = 7.655) (Fig. 5). This observation remained consistent in the sensitivity analysis (Fig. S11). Similarly, meta-regression did not show a statistically significant dose-dependent relationship between total dose and HDL-C levels (coefficient = 0.0037 mg/dL per g, p = 0.2729) (Fig. S12). Moreover, it didn’t reveal a significant relationship between daily dose and HDL-C (coefficient = 0.1370 mg/dL per g/day, p = 0.3200) (Fig. S13).

Fig. 5

Forest plot of overall effects of taurine on high density lipoprotein-cholesterol (HDL-C).

Publication bias

Funnel plot analysis for all investigated outcomes (SBP, DBP, FBG, TG, and HDL-C) indicated no evidence of publication bias. The distribution effect sizes were symmetric, as confirmed by Egger’s regression test, with p values exceeding 0.5 for all outcomes (p = 0.439, p = 0.213, p = 0.083, p = 0.166, and p = 0.158, respectively) (Figs. S14–S17).

Secondary outcomesEffects of taurine on body composition

Taurine supplementation did not significantly impact BW or BMI compared to the control group. The pooled effect size for BW change was minimal and non-significant (WMD: −0.642 kg, 95% CI: −1.494 to 0.209, p = 0.139) (Fig. S18a). Similarly, the effect size for BMI change was not statistically significant (WMD: −0.296 kg, 95% CI: −0.889 to 0.296, p = 0.327) (Fig. S18b). These findings were further supported by a sensitivity analysis with consistent non-significant effects of taurine on both BW and BMI (Fig. S18c, d).

Effects of taurine on lipid profiles

Taurine demonstrated a significant beneficial effect on lipid profiles. Compared to the control group, taurine supplementation significantly reduced both TC and LDL-C levels. The pooled effect size showed a notable decrease in TC (WMD: −8.305 mg/dL, 95% CI: −13.771 to −2.929, p = 0.003) (Fig. S19a), and a similar statistically significant effect was observed for LDL-C levels (WMD: −6.495 mg/dL, 95% CI: −10.912 to −2.079, p = 0.004) (Fig. S19b). These findings were further validated by a sensitivity analysis showing consistent significant effects of taurine on both TC and LDL-C reduction (Fig. S19c and Fig. S19d).

Effects of taurine on glycemic status

Taurine supplementation positively impacted several glycemic markers. Pooled effect sizes revealed significant reductions in HbA1c (WMD: −0.341%, 95% CI: −0.709 to −0.028, p = 0.070) (Fig. S20a), HOMA index (WMD: −0.693, 95% CI: −1.133 to −0.252, p = 0.002) (Fig. S20b), and fasting insulin levels (WMD: −1.521 mU/L, 95% CI: −2.591 to −0.451, p = 0.005) (Fig. S20c) compared to the control group. A sensitivity analysis showed a consistently non-significant effect on HbA1c reduction (Fig. S20d) but maintained consistent significant effects on both HOMA and fasting insulin (Fig. S20e, f).

Adverse effects

Meta-analysis of the treatment-associated adverse effect rates showed no significant differences between the taurine and control groups (odds ratio = 1.481, 95% CI = 0.843–2.604, p = 0.172) (Fig. S17).