Meta-analysis results.

N: number of studies included; OR: odds ratio; Ph: p value for heterogeneity; BC: breast cancer; LC: lung cancer; EC: esophageal cancer; CC: cervical cancer GC: gastric cancer & cardiac cancer AL: acute lymphoblastic leukemia & acute myeloid leukemia OC: ovarian cancer CHN: cancers of head and neck PB: population-based; HB: hospital-based; *OR with statistical significance; large: studies with more than 1000 participants; small: studies with less than 1000 participants; PCR-RFLP: Polymerase chain reaction-restriction fragment length polymorphism; aOR: estimates for fixed effects model.