TABLE 1.
Summary of included health outcomes and their associations with the Dietary Inflammatory Index within the general population
| Outcome | Study design included in MA | Level of comparison | Studies, n | Participants, n | Cases, n | Type of effect size metric | Effect size (95% CI) | 95% CI prediction intervals | P | I 2 | Largest study effect size (95% CI) | Publication bias | Small-study effect or excess significance bias | Evidence class |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Mortality | ||||||||||||||
| All-cause mortality (53) | Prospective | High versus low | 12 | 220,206 | 44,809 | RR | 1.235 (1.157, 1.318) | 1.01, 1.51 | 2.27 × 10−10 | 71.5% | 1.16 (1.1, 1.22) | Yes | Small-study effect | II |
| Cancer mortality (36) | Prospective | High versus low | 11 | 229,448 | 9497 | OR | 1.229 (1.067, 1.415) | 8.30 × 10−1, 1.82 | 4.27 × 10−3 | 54.1% | 1.33 (1.01, 1.76) | No | Neither | IV |
| CVD mortality (34) | Prospective | High versus low | 6 | 93,866 | 11,094 | OR | 1.374 (1.114, 1.696) | 7.00 × 10−1, 2.70 | 3.01 × 10−3 | 77.2% | 1.09 (1.01, 1.18) | Yes | Small-study effect | IV |
| CHD mortality (34) | Prospective | High versus low | 3 | 31,278 | 3,686 | RR | 1.634 (1.012, 2.636) | 1.00 × 10−2, 4.34 × 102 | 4.45 × 10−2 | 76.7% | 1.17 (1.05, 1.3) | Yes | Small-study effect | IV |
| Cancer risk | ||||||||||||||
| Overall cancer (30) | Case-control and Prospective | High versus low | 44 | 1,299,621 | 48,345 | RR | 1.599 (1.466, 1.745) | 1.01, 2.52 | 5.08 × 10−26 | 75.3% | 1.4 (1.28, 1.53) | Yes | Small-study effect | II |
| Colorectal cancer (30) | Case-control and Prospective | High versus low | 11 | 975,683 | 20,076 | RR | 1.426 (1.280, 1.589) | 1.03, 1.98 | 1.26 × 10−10 | 69.1% | 1.4 (1.28, 1.53) | No | Small-study effect | II |
| Prostate cancer (55) | Case-control and Prospective | High versus low | 10 | 52,943 | 5,326 | OR | 1.727 (1.341, 2.226) | 8.00 × 10−1, 3.74 | 2.35 × 10−5 | 78.2% | 1.07 (0.95, 1.2) | Yes | Small-study effect | III |
| Pancreatic cancer (29) | Case-control | High versus low | 2 | 3,551 | 1,143 | RR | 2.524 (1.941, 3.281) | Not estimable* | 4.73 × 10−12 | 0.0% | 2.48 (1.5, 4.1) | Not estimable* | No excess significance* | II |
| Respiratory cancer (pooled) (28) | Case-control | High versus low | 18 | 17,514 | 4,834 | OR | 2.274 (1.894, 2.729) | 1.24, 4.18 | 1.13 × 10−18 | 60.2% | 2.08 (1.47, 2.93) | Yes | Small-study effect | II |
| Esophageal cancer (28) | Case-control | High versus low | 5 | 4,645 | 1,310 | OR | 2.530 (1.738, 3.682) | 7.50 × 10−1, 8.85 | 1.25 × 10−6 | 71.7% | 1.71 (1.54, 1.9) | Yes | Small-study effect | III |
| Laryngeal cancer (28) | Case-control | High versus low | 3 | 2,805 | 997 | OR | 2.046 (0.848, 4.934) | 0.00, 9.08 × 104 | 1.11 × 10−1 | 85.6% | 3.3 (2.06, 5.28) | Yes | Neither | V |
| Oral cancer (28) | Case-control | High versus low | 3 | 4,785 | 1,366 | OR | 2.229 (1.735, 2.865) | 4.00 × 10−1, 1.13 × 101 | 3.72 × 10−10 | 0.0% | 2.08 (1.47, 2.93) | No | Neither | II |
| Pharyngeal cancer (28) | Case-control | High versus low | 7 | 5,279 | 1,161 | OR | 2.019 (1.544, 2.640) | 1.17, 3.48 | 2.81 × 10−7 | 20.3% | 1.64 (0.93, 2.89) | No | Neither | III |
| Lung cancer (52) | Prospective | High versus low | 3 | 149,929 | 2,453 | RR | 1.304 (1.130, 1.504) | 5.20 × 10−1, 3.29 | 2.71 × 10−4 | 0.0% | 1.28 (1.09, 1.51) | No | Neither | III |
| Breast cancer (32) | Case-control and Prospective | High versus low | 12 | 347,147 | 30,052 | RR | 1.335 (1.142, 1.560) | 7.60 × 10−01, 2.33 | 2.79 × 10−4 | 89.9% | 0.99 (0.91, 1.07) | Yes | Small-study effect | III |
| Ovarian cancer (32) | Case-control | High versus low | 4 | 7,982 | 3,104 | RR | 1.414 (1.214, 1.647) | 1.01, 1.98 | 8.57 × 10−6 | 0.0% | 1.47 (1.07, 2.01) | No | Neither | III |
| Gastric cancer (31) | Case-control and Prospective | High versus low | 3 | 2,118 | 700 | RR | 2.120 (1.411, 3.183) | 4.00 × 10−02, 1.17 × 102 | 2.93 × 10−4 | 42.7% | 1.63 (1.15, 2.29) | Yes | Small-study effect | IV |
| Endometrial cancer (32) | Case-control | High versus low | 2 | 1,966 | 751 | RR | 1.881 (0.803, 4.407) | Not estimable* | 1.46 × 10−1 | 68.6% | 1.34 (0.96, 1.87) | Not estimable* | No excess significance* | V |
| Kidney cancer (33) | Case-control and Prospective | High versus low | 2 | 36,118 | 1,030 | RR | 1.463 (1.157, 1.850) | Not estimable* | 1.49 × 10−3 | 0.0% | 1.52 (1.09, 2.13) | Not estimable* | No excess significance* | IV |
| Urothelial cancer (36) | Case-control and Prospective | High versus low | 2 | 42,869 | 1,069 | OR | 1.526 (0.972, 2.397) | Not estimable* | 6.63 × 10−2 | 65.2% | 1.24 (0.9, 1.7) | Not estimable* | No excess significance* | V |
| Cardiovascular disease risk | ||||||||||||||
| Hypertension (50) | Cross-sectional and Prospective | High versus low | 15 | 71,729 | 24,648 | OR | 1.133 (1.013, 1.266) | 8.00 × 10−1, 1.60 | 2.81 × 10−2 | 55.6% | 1.21 (1.02, 1.43) | No | Neither | IV |
| Cardiovascular (34) | Cross-sectional and Prospective | High versus low | 6 | 57,781 | 3,022 | OR | 1.345 (1.110, 1.631) | 8.40 × 10−1, 2.17 | 2.52 × 10−3 | 36.3% | 2.03 (1.06, 3.89) | No | Neither | IV |
| Myocardial infarction (34) | Case-control and Prospective | High versus low | 6 | 37,065 | 2,497 | RR | 1.717 (1.419, 2.077) | 1.31, 2.25 | 2.64 × 10−8 | 0.0% | 2.28 (1.09, 4.75) | Yes | Neither | I |
| IHD-CHD risk (34) | Cross-sectional and Prospective | High versus low | 3 | 23,962 | 875 | RR | 1.272 (0.874, 1.853) | 2.00 × 10−2, 7.83 × 101 | 2.09 × 10−1 | 62.2% | 0.96 (0.72, 1.28) | Yes | Small-study effect | V |
| Stroke (34) | Cross-sectional and Prospective | High versus low | 3 | 30,408 | 569 | RR | 1.099 (0.605, 1.999) | 0.00, 8.61 × 102 | 7.56 × 10−1 | 65.5% | 1.56 (1.21, 2.01) | No | Excess significance | V |
| Angina (34) | Cross-sectional and Prospective | High versus low | 2 | 23,436 | 442 | RR | 0.793 (0.561, 1.120) | Not estimable* | 1.88 × 10−1 | 0.0% | 0.83 (0.54, 1.28) | Not estimable* | No excess significance* | V |
| Mental health risk | ||||||||||||||
| Depression (35) | Cross-sectional and Prospective | High versus low | 15 | 55,490 | 4,884 | OR | 1.441 (1.225, 1.695) | 0.87 × 10−1, 2.40 | 1.02 × 10−6 | 58.8% | 1.46 (1.1, 1.94) | No | Neither | III |
| Metabolic risk markers | ||||||||||||||
| Metabolic syndrome (54) | Case-control and Prospective | High versus low | 5 | 15,161 | 2,242 | RR | 1.006 (0.816, 1.242) | 5.80 × 10−1, 1.74 | 9.53 × 10−1 | 32.6% | 0.86 (0.6, 1.23) | No | Neither | V |
| HbA1c (50) | Cross-sectional | Continuous | 3 | 23,138 | — | WMD | 0.615 (0.266, 0.965) | −3.66, 4.89 | 5.60 × 10−4 | 87.5% | 0.4 (0.34, 0.46) | No | No small-study effect* | III |
| Fasting blood glucose (50) | Case-control and Prospective | Continuous | 15 | 93,739 | — | WMD | 1.083 (0.100, 2.065) | −2.38, 4.54 | 3.08 × 10−2 | 89.0% | 3.7 (0.04, 5.36) | No | No small-study effect* | IV |
| Insulin (50) | Cross-sectional | Continuous | 6 | 38,359 | — | WMD | 0.829 (0.169, 1.488) | −1.27, 2.93 | 1.38 × 10−2 | 86.5% | 2.47 (1.64, 3.3) | No | No small-study effect* | IV |
| HOMA-IR (50) | Cross-sectional | Continuous | 7 | 41,645 | — | WMD | 0.191 (0.021, 0.362) | −3.90 × 10−01, 7.70 × 10−01 | 2.80 × 10−2 | 93.2% | 0.88 (0.67, 1.09) | No | No small- study effect* | IV |
| Hyperglycemia (50) | Cross-sectional | High versus low | 11 | 30,424 | 4,883 | OR | 1.130 (0.948, 1.347) | 6.70 × 10−01, 1.91 | 1.73 × 10−1 | 60.7% | 1.09 (0.83, 1.44) | Yes | Small-study effect | V |
| Central obesity (51) | Cross-sectional | High versus low | 13 | 25,435 | 5,121 | OR | 1.162 (0.945, 1.429) | 6.00 × 10−01, 2.24 | 1.54 × 10−1 | 65.4% | 1.35 (0.94, 1.94) | No | Small-study effect | V |
| Waist circumference (51) | Case-control and Prospective | Continuous | 25 | 78,828 | — | WMD | 1.782 (0.722, 2.842) | −3.00, 6.56 | 9.82 × 10−4 | 100.0% | 3.7 (2.81, 4.59) | No | Neither | III |
| Waist-to-hip ratio (51) | Case-control and Prospective | Continuous | 11 | 16,685 | — | WMD | −0.005 (−0.039, 0.029) | −1.10 × 10−01, 1.00 × 10−01 | 7.59 × 10−1 | 87.1% | 0.0 (−0.01, 0.01) | No | No small- study effect* | V |
| Systolic blood pressure (50) | Case-control, Cohort, and Prospective | Continuous | 15 | 87,202 | — | WMD | 1.230 (0.283, 2.177) | −2.29, 4.76 | 1.09 × 10−2 | 91.5% | 5.4 (4.52, 6.28) | No | No small-study effect* | IV |
| Diastolic blood pressure (50) | Case-control and Prospective | Continuous | 12 | 79,871 | — | WMD | 0.009 (−0.686, 0.703) | −2.40, 2.42 | 9.81 × 10−1 | 91.6% | 1.7 (0.99, 2.41) | No | No small-study effect* | V |
*
Either tests for small-study effect, excess significance, or both, could not be conducted due to small sample size of included studies.
Evidence class criteria—class I (convincing): statistical significance at P < 10−6, >1000 cases (or >20,000 participants for continuous outcomes), the largest component study reported a significant effect (P < 0.05); the 95% prediction interval excluded the null, no large heterogeneity (I2 < 50%), no evidence of small-study effects (P > 0.10) and excess significance bias (P > 0.10); class II (highly suggestive): significance at P < 10−6, >1000 cases (or >20,000 participants for continuous outcomes), the largest component study reported a significant effect (P ≤ 0.05); class III (suggestive): statistical significance at P < 10−3, >1000 cases (or >20,000 participants for continuous outcomes); and class IV (weak): the remaining significant associations at P < 0.05.