Subgroup analysis for different IBD and age
| Subgroup | Studies (n) | OR | 95% CI | Pheterogeneity |
| UC | ||||
| Cohort study | 3 | 1.29 | 1.13 to 1.45 | 0.58 |
| Case–control study | 1 | 0.88 | 0.82 to 0.96 | – |
| All studies | 4 | 1.12 | 0.81 to 1.42 | <0.001 |
| Crohn’s disease | ||||
| Cohort study | 3 | 1.28 | 1.10 to 1.47 | 0.60 |
| Case–control study | 1 | 0.83 | 0.74 to 0.93 | – |
| All studies | 4 | 1.13 | 0.81 to 1.45 | <0.001 |
| Age | ||||
| <50 years old | 2 | 1.18 | 0.73 to 1.62 | 0.70 |
| ≥60 years old | 3 | 1.32 | 1.16 to 1.47 | 0.91 |