Garlic Supplementation Reduces Circulating C-reactive Protein, Tumor Necrosis Factor, and Interleukin-6 in Adults: A Systematic Review and Meta-analysis of Randomized Controlled Trials.
What this study found
Garlic supplementation reduced circulating inflammatory markers in adults. Compared with controls, pooled effects showed lower CRP (WMD -0.61 mg/L, 95% CI -1.12, -0.11, P = 0.018), IL-6 (WMD -0.73 ng/L, 95% CI -1.06, -0.40, P < 0.001), and TNF (WMD -0.26 ng/L, 95% CI -0.41, -0.12, P < 0.001). Effects on adiponectin (WMD 0.18 μg/L, P = 0.35) and leptin (WMD -1.25 μg/L, P = 0.07) were not significant. The authors concluded that garlic may have anti-inflammatory effects, but confirmation in additional randomized trials is needed.
- Study & population
- Systematic review and meta-analysis of 16 randomized controlled trials in adults aged 18 to 75 years.
- Intervention
- Garlic supplementation was tested in randomized trials using aged garlic extract or garlic powder tablets.
- Key limitation
- Results were based on a relatively small evidence base with only 16 trials and substantial between-study variation in dose, duration, population health status, and garlic formulation.
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Open PDFOriginal abstract
BACKGROUND Conflicting findings on the effects of garlic supplementation on inflammatory biomarkers have been observed in randomized clinical trials (RCTs). OBJECTIVES The aim of this study was to summarize study results regarding the effects of garlic supplementation on serum inflammatory biomarkers in adults. METHODS We searched Scopus, PubMed, Google Scholar and Cochrane library databases for relevant papers published until April 2018, using keywords such as "garlic" and "inflammatory biomarker." We included RCTs that 1) were conducted in adults, 2) examined the effects of garlic supplementation on inflammatory biomarkers compared to a control group, and 3) reported sufficient data on inflammatory biomarkers. Results were reported as weighted mean differences (WMD) with 95% CI using random effects models. Cochrane's Q and I-squared (I2) tests were used to determine heterogeneity among studies. Funnel plots and Egger's regression test were used to assess publication bias. RESULTS Sixteen RCTs were included. Garlic doses ranged from 12 to 3600 mg/d, and intervention duration ranged from 2 to 52 wk. Garlic administration significantly reduced serum C-reactive protein (CRP) (n = 13) (WMD: -0.61 mg/L, 95% CI: -1.12, -0.11, P = 0.018, I2 = 76.9%), IL-6 (n = 5) (WMD: -0.73 ng/L, 95% CI: -1.06, -0.40, P < 0.001, I2 = 0%), and TNF (n = 7) (WMD: -0.26 ng/L, 95% CI: -0.41, -0.12, P < 0.001, I2 = 0.0%), compared to controls. However, the effect of garlic supplementation on serum adiponectin (n = 3) (WMD: 0.18 µg/L, 95% CI: -0.21, 0.57, P = 0.35, I2 = 60.7%) and leptin (n = 2) (WMD: -1.25 µg/L, 95% CI: -2.64, 0.14, P = 0.07, I2 = 0.0%) concentrations were not significant. CONCLUSION In this meta-analysis of RCTs, we found that garlic supplementation reduced serum concentrations of CRP, TNF, IL-6, but did not affect serum adiponectin and leptin in adults. More RCTs are needed to test the effects of garlic supplementation on inflammation.