Thirty-four case-control studies (number of patients in these studies ranged from 140 to 33,585) and one cohort study (200 patients) were included.
Statistical tests found significant heterogeneity among individual studies (chi-squared=49.8, d.f.=33, p<0.05). The pooled OR for all studies was 1.12 (95% confidence interval, CI: 1.03, 1.22).
Subset analyses: pooled OR for women, 1.14 (95% CI: 1.01, 1.28); pooled OR for men, 1.06 (95% CI: 0.9, 1.24); pooled OR for right-sided colorectal cancer, 1.86 (95% CI: 1.31, 2.65); pooled OR for left-sided colorectal cancer, 0.9 (95% CI: 0.69, 1.19).