Table 3. Efficacy of vitamin and antioxidant supplements in the prevention of bladder cancer in subgroup meta-analyses.
| Factors | No. of trials | RR (95% CI) | Heterogeneity, I2, % | Model |
|---|---|---|---|---|
| All | 14 | 1.04 (0.92–1.17) | 39.7 | Fixed-effects |
| Type of supplements | ||||
| Vitamin A | 5 | 0.86 (0.65–1.13) | 61.7 | Random-effects |
| Vitamin A (25,000–40,000 IU) | 3 | 0.85 (0.54–1.34) | 79.0 | Random-effects |
| Fenretinide (200 mg/day) | 2 | 0.85 (0.63–1.16) | 0.0 | Fixed-effects |
| Vitamin B6 | 3 | 0.77 (0.49–1.20) | 78.8 | Random-effects |
| Low dose (25 mg/day) | 2 | 1.00 (0.83–1.21) | 34.8 | Fixed-effects |
| High dose (100 mg/day) | 1 | 0.50 (0.32–0.78) | NA | NA |
| Vitamin C | 2 | 0.74 (0.36–1.54) | 88.8 | Random-effects |
| Vitamin D | 1 | 1.05 (0.85–1.29) | NA | NA |
| Vitamin E | 6 | 0.91 (0.69–1.19) | 60.9 | Random-effects |
| Low dose (50 mg/day) | 1 | 1.09 (0.80–1.50) | NA | NA |
| High dose (400 IU/day) | 5 | 0.84 (0.58–1.22) | 67.0 | Random-effects |
| Beta-carotene | 6 | 1.19 (0.96–1.46) | 0.0 | Fixed-effects |
| Low dose (20–30 mg/day) | 5 | 1.18 (0.96–1.45) | 0.0 | Fixed-effects |
| High dose (75 mg/day) | 1 | 3.17 (0.13–76.99) | NA | NA |
| Beta-carotene alone | 3 | 1.44(1.00–2.09) | 0.0 | Fixed-effects |
| Folic acid | 1 | 1.05 (0.85–1.29) | NA | NA |
| Selenium | 2 | 1.09 (0.81–1.46) | 0.0 | Fixed-effects |
| Type of cancer prevention | ||||
| Primary | 8 | 1.18 (0.99–1.41) | 0.0 | Fixed-effects |
| Secondary | 6 | 0.79 (0.62–1.02) | 54.1 | Random-effects |
| Methodological quality | ||||
| High quality | 12 | 1.06 (0.94–1.20) | 41.1 | Fixed-effects |
| Low quality | 2 | 0.71 (0.47–1.07) | 0.0 | Fixed-effects |
| Duration of treatment | ||||
| < 5 | 11 | 0.96 (0.84–1.10) | 33.5 | Fixed-effects |
| ≥ 5 | 3 | 1.22 (0.97–1.55) | 0.0 | Fixed-effects |
| Provider of supplements | ||||
| Pharmaceutical | 10 | 1.09 (0.95–1.24) | 44.9 | Fixed-effects |
| Non-pharmaceutical | 4 | 0.75 (0.57–0.99) | 0.0 | Fixed-effects |
| High quality | 2 | 0.78 (0.53–1.15) | 0.0 | Fixed-effects |
| Low quality | 2 | 0.71 (0.47–1.07) | 0.0 | Fixed-effects |
| Type of control | ||||
| No treatment | 3 | 0.75 (0.52–1.09) | 0.0 | Fixed-effects |
| Placebo | 11 | 1.06 (0.94–1.20) | 43.6 | Fixed-effects |
| No. of participants in each trial | ||||
| < 10,000 | 9 | 0.92 (0.79–1.07) | 40.7 | Fixed-effects |
| ≥ 10,000 | 5 | 1.16 (0.97–1.39) | 0.0 | Fixed-effects |
NA = not applicable, RR = relative risk.