Table 2.
Subgroup analyses for the effect of vitamin E intake on glycemic indices and insulin resistance in patients with diabetes
| Effect size, n | WMD (95% CI)a | P-within2 | Ib (%)c | P-heterogeneityd | |
|---|---|---|---|---|---|
| Vitamin E intake on fasting blood glucose | |||||
| Overall | 34 | -3.35 (-8.10, 1.40) | 0.16 | 82.2 | < 0.001 |
| Intervention duration (week) | |||||
| < 10 | 15 | -6.04 (-9.88, -2.21) | 0.002 | 19.1 | 0.24 |
| ≥ 10 | 19 | -2.86 (-10.39, 4.66) | 0.45 | 89 | < 0.001 |
| Type of vitamin E | |||||
| α-tocopherol | 21 | -3.75 (-11.21, 3.71) | 0.32 | 88.4 | < 0.001 |
| Tocoterienol | 2 | -4.44 (-8.91, 0.03) | 0.05 | 0.0 | 0.62 |
| Mixed-tocopherols | 1 | 9.00 (-14.72, 32.71) | 0.45 | 0.0 | - |
| Unclear | 10 | -5.24 (-9.59, -0.88) | 0.01 | 3.3 | 0.40 |
| Dosage of vitamin E (mg/day) | |||||
| < 500 | 15 | -7.13 (-14.99, 0.73) | 0.07 | 87.3 | < 0.001 |
| ≥ 500 | 19 | -0.22 (-1.73, 1.29) | 0.77 | 0.0 | 0.55 |
| Study location | |||||
| Western countries | 16 | -0.33 (-1.85, 1.19) | 0.67 | 0.0 | 0.52 |
| Non-Western countries | 18 | -4.53 (-11.59, 2.53) | 0.20 | 85.1 | < 0.001 |
| Study design | |||||
| Crossover | 3 | -7.07 (-15.46, 1.32) | 0.09 | 30.1 | 0.23 |
| Parallel | 31 | -2.82 (-8.08, 2.44) | 0.29 | 83.4 | < 0.001 |
| Blinded | 25 | -3.96 (-9.39, 1.47) | 0.15 | 86.5 | < 0.001 |
| Non-blinded | 9 | -2.81 (-9.62, 3.99) | 0.41 | 0 | 0.49 |
| Type of diabetes | |||||
| T2DM | 27 | -4.42 (-9.63, 0.76) | 0.09 | 85 | < 0.001 |
| T1DM | 6 | 0.87 (-10.53, 12.27) | 0.88 | 0.0 | 0.94 |
| Diabetic nephropathy | 1 | 10.00 (-5.80, 25.80) | 0.21 | 0.0 | |
| Risk of bias e | |||||
| High | 28 | -4.10 (-9.81, 1.61) | 0.16 | 83.2 | < 0.001 |
| Low | 6 | 0.04 (-9.71, 9.78) | 0.994 | 79.7 | < 0.001 |
| Vitamin E intake on HbA1c | |||||
| Overall | 36 | -0.21 (-0.33, -0.09) | 0.001 | 76.6 | < 0.001 |
| Intervention duration (week) | |||||
| < 10 | 13 | -0.24 (-0.48, 0.00) | 0.05 | 75.3 | < 0.001 |
| ≥ 10 | 23 | -0.24 (-0.48, 0.00) | 0.01 | 78.2 | < 0.001 |
| Type of vitamin E | |||||
| α-tocopherol | 19 | -0.18 (-0.36, 0.01) | 0.06 | 76.3 | < 0.001 |
| Tocoterienol | 6 | -0.09 (-0.15, -0.04) | < 0.001 | 0.0 | 0.81 |
| unclear | 11 | -0.71 (-1.21, -0.21) | 0.005 | 86 | < 0.001 |
| Dosage of Vitamin E (mg/day) | |||||
| ≥ 500 | 18 | -0.41 (-0.68, -0.14) | 0.003 | 80.2 | < 0.001 |
| < 500 | 18 | -0.10 (-0.22, 0.02) | 0.09 | 62.2 | < 0.001 |
| Study location | |||||
| Western countries | 16 | -0.40 (-0.69, -0.11) | 0.007 | 79.5 | < 0.001 |
| Non-Western countries | 20 | -0.12 (-0.24, 0.00) | 0.05 | 66.5 | < 0.001 |
| Study design | |||||
| Crossover | 6 | -0.09 (-0.15, -0.04) | 0.001 | 0 | 0.54 |
| Parallel | 30 | -0.26 (-0.43, -0.10) | 0.002 | 80.1 | < 0.001 |
| Blinded | 27 | -0.16 (-0.29, -0.04) | 0.01 | 74.8 | < 0.001 |
| Non-blinded | 9 | -0.68 (-1.20, -0.17) | 0.01 | 82.8 | < 0.001 |
| Type of diabetes | |||||
| T2DM | 23 | -0.16 (-0.30, -0.02) | 0.02 | 78.7 | < 0.001 |
| T1DM | 9 | -0.76 (-1.37, -0.15) | 0.01 | 80.8 | < 0.001 |
| Diabetic nephropathy | 2 | -0.24 (-0.56, 0.07) | 0.12 | 0 | 0.90 |
| T2DM & T1DM | 1 | 0.00 (-0.34, 0.34) | 1.00 | 0 | - |
| Diabetic neuropathy | 1 | -0.18 (-0.66, 0.30) | 0.45 | 0 | - |
| Risk of bias e | |||||
| High | 30 | -0.28 (-0.42, -0.13) | < 0.001 | 79.4 | < 0.001 |
| Low | 6 | 0.01 (-0.17, 0.18) | 0.95 | 25.3 | 0.24 |
| Vitamin E intake on fasting Insulin concentrations | |||||
| Overall | 18 | -1.05 (-1.53, -0.58) | < 0.001 | 52.7 | 0.005 |
| Intervention duration (week) | |||||
| < 10 | 8 | -0.88 (-1.27, -0.49) | < 0.001 | 0.0 | 0.80 |
| ≥ 10 | 10 | -1.06 (-1.86, -0.26) | 0.009 | 57.8 | 0.01 |
| Type of vitamin E | |||||
| α-tocopherol | 12 | -0.87 (-1.60, -0.14) | 0.01 | 53.5 | 0.01 |
| Tocoterienol | 1 | -0.88 (-1.33, -0.43) | < 0.001 | 100 | - |
| Mixed-tocopherols | 1 | -1.40 (-5.94, 3.14) | 0.54 | 100 | - |
| Unclear | 4 | -1.54 (-2.79, -0.29) | 0.01 | 23.1 | 0.27 |
| Dosage of Vitamin E (mg/day) | |||||
| < 500 | 9 | -1.06 (-1.73, -0.39) | 0.002 | 15.1 | 0.30 |
| ≥ 500 | 9 | -1.00 (-1.68, -0.32) | 0.004 | 66.1 | 0.003 |
| Study location | |||||
| Western countries | 6 | -1.28 (-1.92, -0.64) | < 0.001 | 61.1 | 0.02 |
| Non-Western countries | 12 | -0.87 (-1.56, -0.19) | 0.01 | 35.3 | 0.10 |
| Study design | |||||
| Blinded | 16 | -1.02 (-1.53, -0.52) | < 0.001 | 56.6 | 0.003 |
| Non-blinded | 2 | -0.18 (-6.53, 6.18) | 0.05 | 28.1 | 0.23 |
| Type of diabetes | |||||
| T2DM | 17 | -1.03 (-1.55, -0.51) | < 0.001 | 55.1 | 0.003 |
| Diabetic nephropathy | 1 | -1.20 (-2.31, -0.09) | 0.03 | 0 | - |
| Risk of bias e | |||||
| High | 12 | -1.05 (-1.85, -0.24) | 0.011 | 44.6 | 0.047 |
| Low | 6 | -0.89 (-1.27, -0.51) | < 0.001 | 0 | 0.46 |
| Vitamin E intake on HOMA-IR | |||||
| Overall | 12 | -0.44 (-0.82, -0.05) | 0.02 | 83.4 | < 0.001 |
| Intervention duration (week) | |||||
| < 10 | 4 | -0.18 (-0.43, 0.07) | 0.15 | 6.5 | 0.36 |
| ≥ 10 | 8 | -0.73 (-1.36, -0.08) | 0.02 | 87.6 | < 0.001 |
| Type of vitamin E | |||||
| α-tocopherol | 8 | -0.72 (-1.29, -0.15) | 0.01 | 87.5 | < 0.001 |
| Tocoterienol | 1 | -0.10 (-0.39, 0.19) | 0.49 | 0 | - |
| Unclear | 3 | 0.0 (-0.57, 0.58) | 0.98 | 0 | 0.67 |
| Dosage of Vitamin E (mg/day) | |||||
| < 500 | 7 | -0.98 (-1.83, -0.13) | 0.02 | 88.7 | < 0.001 |
| ≥ 500 | 5 | -0.17 (-0.55, 0.20) | 0.36 | 69.5 | 0.01 |
| Study location | |||||
| Western countries | 2 | -0.33 (-0.74, 0.08) | 0.11 | 86.0 | 0.007 |
| Non-Western countries | 10 | -0.59 (-1.26, 0.08) | 0.08 | 84.6 | < 0.001 |
| Type of diabetes | |||||
| T2DM | 11 | -0.47 (-0.88, -0.05) | 0.02 | 84.8 | < 0.001 |
| Diabetic nephropathy | 1 | -0.20 (-1.03, 0.63) | 0.63 | 0 | - |
| Risk of bias e | |||||
| High | 7 | -0.95 (-1.93, 0.02) | 0.054 | 88.8 | < 0.001 |
| Low | 5 | -0.18 (-0.38, 0.02) | 0.084 | 0 | 0.518 |
Abbreviations: HbA1C Hemoglobin A1c, WMD weighted mean difference, HOMA-IR homeostatic model assessment for insulin resistance
aObtained from the random-effects model
bRefers to the mean (95% CI)
cInconsistency, percentage of variation across studies due to heterogeneity
dObtained from the Q-test
eIf a trial had “low risk” for all domains of the Cochrane Risk of Bias Assessment tool, it was considered a high-quality study with a totally low risk of bias