Table 2.
Summary of pooled risk ratios of bladder cancer by study design, sex, geographical region, and source of intake
| Subgroup | Number of studies | Pooled RR (95% CI) | Q-test for heterogeneity p value (I2 score) | Egger’s test p value | Begg’s test p value |
|---|---|---|---|---|---|
| Vitamin C | 20 | 0.90 (0.79, 1.00) | 0.02 (43.7%) | 0.085 | 0.064 |
| Cohort studies | 9 | 0.94 (0.81, 1.08) | 0.294 (16.6%) | 0.67 | 1 |
| Case-control studies | 11 | 0.85 (0.69, 1.00) | 0.012 (56.0%) | 0.041 | 0.087 |
| European studies | 8 | 0.93 (0.81, 1.06) | 0.206 (27.8%) | 0.541 | 0.711 |
| US studies | 11 | 0.85 (0.76, 0.95) | 0.011 (56.2%) | 0. 213 | 0.07 |
| Japanese study | 1 | 0.81 (0.49, 1.35) | |||
| Men | 6 | 0.86 (0.71, 1.01) | 0.565 (0) | 0.847 | 1 |
| Women | 3 | 0.61 (0.25, 0.97) | 0.026 (49.6%) | 0.67 | 1 |
| Diet | 11 | 0.89 (0.75, 1.02) | < 0.001 (83.2%) | 0.117 | 0.086 |
| Supplement | 7 | 0.74 (0.54, 0.93) | 0.041 (54.3%) | 0.423 | 0.368 |
| Diet plus supplement | 8 | 0.82 (0.65, 1.00) | 0.015 (41.0%) | 0.641 | 0.536 |
| Vitamin E | 15 | 0.82 (0.74, 0.90) | 0.474 (0) | 0.534 | 0.138 |
| Cohort studies | 7 | 0.85 (0.72, 0.99) | 0.262 (21.1%) | 0.667 | 1 |
| Case-control studies | 7 | 0.80 (0.69, 0.91) | 0.6 (0) | 0.108 | 0.133 |
| European studies | 6 | 0.84 (0.71, 0.98) | 0.545 (0) | 0.272 | 0.260 |
| US studies | 8 | 0.82 (0.71, 0.92) | 0.259 (21.5%) | 0.280 | 0.536 |
| Japanese study | 1 | 0.68 (0.41, 1.12) | |||
| Men | 5 | 0.74 (0.60, 0.88) | 0.36 (8.1%) | 0.309 | 0.806 |
| Women | 2 | 0.83 (0.07, 1.06) | 0.008 (85.9%) | ||
| Diet | 7 | 0.78 (0.65, 0.90) | 0.583 (0) | 0.0321 | 0.0161 |
| Supplement | 5 | 0.79 (0.60, 0.97) | 0.251 (25.6%) | 0.166 | 0.221 |
| Diet plus supplement | 7 | 0.81 (0.63, 0.99) | 0.129 (39.4%) | 0.272 | 0.764 |
Abbreviations: CI, confidence interval; US, United States.
1
Trim and fill method was used to recalculate the summary RE and the result did not changed, suggesting the stability of the analysis.