Table 2.
Subgroup analyses of studies on vitamin E intake and prostate cancer.
| Type of Vitamin E Intake | No. of Studies | Sample Size | RR (95% CI) | I2 Value (%) | p Value for Subgroup Differences |
|---|---|---|---|---|---|
| Dietary intake | |||||
| Study design | |||||
| Case-control studies | 13 | 18,322 | 0.93 (0.84–1.02) | 28.34 | 0.289 |
| Cohort studies | 6 | 498,431 | 0.99 (0.93–1.05) | 12.48 | |
| Sample size | |||||
| <1000 | 7 | 4087 | 0.77 (0.54–1.10) | 72.12 | 0.605 |
| >1000 | 12 | 512,666 | 0.98 (0.93–1.03) | 5.22 | |
| Geographical region | |||||
| North America | 8 | 474,184 | 0.99 (0.93–1.06) | 12.40 | 0.036 |
| Europe | 9 | 40,398 | 0.92 (0.84–1.01) | 0.02 | |
| Vitamin E intake a | |||||
| ≥15 mg/day | 10 | 189,841 133,729 |
0.94 (0.86–1.02) | 0.00 | |
| Supplemental intake of vitamin E | |||||
| Study type | |||||
| Observational | 12 | 613,469 | 0.99 (0.95–1.04) | 0.04 | 0.133 |
| Interventional | 6 | 72,879 | 0.96 (0.82–1.13) | 72.90 | |
| Study type | |||||
| Case-control studies | 3 | 7640 | 0.88 (0.63–1.22) | 51.49 | 0.451 |
| Cohort studies | 9 | 605,829 | 1.00 (0.95–1.04) | 0.00 | |
| Sample size | |||||
| <20,000 | 10 | 67,433 | 1.00 (0.91–1.10) | 34.36 | 0.094 |
| >20,000 | 8 | 618,915 | 0.98 (0.94–1.03) | 11.20 | |
| Geographical region | |||||
| North America | 13 | 609,392 | 1.01 (0.97–1.06) | 18.76 | 0.020 |
| Europe | 4 | 69,960 | 0.81 (0.69–0.97) | 33.56 | |
| Dose of supplements used | |||||
| ≥400 IU | 7 | 457,383 | 1.00 (0.93–1.08) | 40.67 | |
| RCTs using dose <400 IU/day | 3 | 48,147 | 0.85 (0.67–1.09) | 69.43 | 0.541 |
| RCTs using dose ≥400 IU/day | 3 | 24,732 | 1.11 (0.97–1.27) | 16.82 | |
| Study population | |||||
| RCTs participants without underlying conditions | 4 | 65,580 | 0.93 (0.74–1.18) | 86.18 | 0.712 |
| RCTs participants with underlying conditions | 2 | 7299 | 0.99 (0.80–1.23) | 0.00 | |
Abbreviations: IU, International units; RCT: Randomized controlled trial. a Recommended daily intake by the Institute of Medicine Panel on Dietary Antioxidants and Related Compounds in the United States. The guidelines for intake may differ from country to country and can vary from 3 mg/day to 15 mg/day [53]. Bolded values represent a statistically significant result at p value < 0.05.