Meta-analysis: Does garlic intake reduce risk of gastric cancer?

In the past 2 decades, various epidemiological studies investigated whether garlic can positively modify the risk of gastric cancer. Garlic contains numerous sulfide compounds, including diallyl trisulfide, which have anticarcinogenic properties. We conducted a meta-analysis to determine if garlic intake reduces the risk of gastric cancer. An electronic search of MEDLINE, PubMed, and EMBASE to June 2014 was completed. There were 14 case control studies, 2 randomized controlled studies, and 1 cohort study that fulfilled our inclusion criteria. We used a random effects model to calculate pooled odds ratios (OR) and 95% confidence intervals (CIs) for risk of gastric cancer with garlic consumption. Meta-analysis of a total of 8,621 cases and 14,889 controls was conducted. Significant variability in duration of garlic intake and reference categories for amount of intake was noted. High, low, and any garlic intake were all associated with reduced risk of gastric cancer. High intake had the most significant risk reduction, OR = 0.49 (95% CI: 0.38-0.62). Heterogeneity was low (I² = 30.85, P = 0.17). A more modest risk reduction was associated with low intake, OR = 0.75 (95% CI: 0.58-0.97). Half of the studies did not separate garlic intake into high or low amounts, intake was only noted as consumption vs. non-consumption. Any amount of consumption still showed a risk reduction similar to low intake, OR = 0.77 (95% CI: 0.60-1.00). Low and any amount of consumption showed moderate heterogeneity (58% and 45%, respectively). Garlic intake appears to be associated with reduced risk of gastric cancer. Further high quality studies are required to confirm this finding and to assess the amount of garlic that needs to be consumed for protective effect.