Background Garlic is a species in the onion genus, Allium. Data have shown that garlic has anti-inflammatory activity; however, the findings are inconclusive and inconsistent. We aimed to evaluate the impact of garlic intake on inflammatory mediators through systematic review and meta-analysis of existing data.

Methods Electronic databases were completely investigated using databases of ISI Web of Science, Medline, Scopus, Cochrane Library and EMBASE until October 2019. A random effects model and the generic reverse variance procedure were used for quantitative data production. Sensitivity analyses and prespecified subgroup were done to evaluate potential heterogeneity. Random effect meta-regression was conducted to investigate the effects of possible confounders on the assessed effect size.

Results Ten trials with one observational study, including 530 participants, met the eligibility criteria. The findings showed reduction in the tumour necrosis factor alpha (TNF-α) (−0.31 pg/mL, 95% CI −1.07 to 0.46) and C reactive protein (CRP) levels (−0.20 mg/L, 95% CI −1.4 to 1.05) following supplementation with garlic, although it had no marked impact on the interleukin 6 (IL-6) level (0.37 pg/mL, 95% CI −0.58 to 1.33). In the subgroup analysis, we found that garlic supplementation significantly decreased TNF-α, highly sensitive CRP and IL-6 levels in subgroups of >8, >6 and ≥4 weeks of intervention duration, respectively, and dose of garlic consumption between 2 and 2.4 g/day.

Conclusion These findings suggested that current evidence may support garlic as an adjunct to pharmacological management of metabolic diseases.

PROSPERO registration number CRD42018108816.