Table 1 Summary risk estimates of the association between waterpipe smoking and health-related outcomes
Outcome | Studies (N) | Participant (N) | Type of effect size metric | Effect size (95% CI) | I2 | 95% CI prediction intervals | Publication bias | Largest study effect size | Small study effect | Certainty of the evidence (GRADE) |
|---|---|---|---|---|---|---|---|---|---|---|
Anthropometric indices | ||||||||||
 BMI | 32 | 10,001 | SMD | 0.08 (− 0.03, 0.20) | 78.72 | (− 0.50, 0.66) | No | 0.24 (− 0.10, 0.57) | Yes | Very low |
 WC | 8 | 4652 | SMD | 0.11 (− 0.11, 0.33) | 87.76 | (− 0.63, 0.85) | NA | 0.34 (0.22, 0.46) | Yes | Very low |
 Weight | 20 | 4198 | SMD | 0.43 (0.16, 0.70) | 93.72 | (− 1.11, 2.01) | Yes | 1.74 (1.51, 1.96) | No | Very low |
Cancers | ||||||||||
 Gastric | 6 | 3764 | OR | 2.11 (1.02, 4.40) | 84.47 | (0.18, 25.34) | NA | 1.86 (1.42, 2.42) | Yes | Very low |
 Lung | 7 | 11,272 | OR | 2.61 (1.28, 5.34) | 94.23 | (0.22, 31.28) | NA | 1.63 (1.30, 2.05) | No | Very low |
 Bladder | 7 | 9131 | OR | 1.57 (1.14, 2.18) | 72.08 | (0.61, 4.02) | NA | 1.42 (1.11, 1.82) | No | Very low |
 Esophageal | 7 | 4783 | OR | 2.95 (1.36, 6.40) | 92.42 | (0.18, 48.15) | NA | 2.06 (1.72, 2.47) | No |  |
Cardiovascular disease risk | ||||||||||
 CVD | 5 | 32,842 | aOR | 1.14 (0.95, 1.36) | 12.77 | (0.73, 1.77) | NA | 1.29 (0.73, 2.27) | Yes | Very low |
 CAD | 8 | 66,784 | OR | 1.56 (1.36, 1.79) | 23.17 | (1.17, 2.07) | NA | 1.67 (1.25, 2.23) | No | Low |
 Stroke | 5 4 | 6606 2734 | Crude OR aOR | 2.66 (2.02, 3.49) 3.10 (2.20, 4.39) | 0 0 | (1.71, 4.13) (1.44, 6.65) | NA NA | 1.06 (0.14, 7.97) 2.47 (2.52, 4.01) | No No | Very low |
 SBP | 21 | 19,491 | SMD | 0.14 (− 0.37, 0.65) | 99.07 | (− 2.38, 2.66) | No | 0.01 (− 0.06,0.06) | No | Very low |
 DBP | 21 | 19,491 | SMD | 0.10 (− 0.20, 0.40) | 97.37 | (− 1.33, 1.53) | No | 0.03 (− 0.03,0.09) | No | Very low |
 Heart rate | 16 | 16,882 | SMD | 0.14 (− 0.08, 0.36) | 92.65 | (− 0.80, 1.08) | No | 0.04 (− 0.02, 0.10) | No | Very low |
 Hypertension | 13 | 40,598 | OR | 0.82 (0.64, 1.04) | 72.72 | (0.39, 1.71) | Yes | 0.86 (0.66, 1.13) | No | Very low |
Neurologic and psychiatric disorders | ||||||||||
 Depression | 4 | 85,361 | aOR | 1.09 (0.88, 1.34) | 95.29 | (− 2.43, 2.77) | NA | 1.30 (1.20, 1.40) | No | Very low |
 Multiple sclerosis | 5 3 | 3477 2287 | Crude OR aOR | 1.37 (0.89, 2.20) 1.46 (0.98, 2.18) | 63.87 36.42 | (0.31, 6.01) NA | NA NA | 1.39 (1.11, 1.75) 1.39 (1.11, 1.75) | Yes Yes | Very low Very low |
Metabolic disease | ||||||||||
 Diabetes | 7 | 35,811 | OR | 1.42 (1.03, 1.95) | 85.46 | (0.53, 3.78) | NA | 0.87 (0.71, 1.07) | Yes | Very low |
 Dyslipidemia | 5 | 19,093 | OR | 0.96 (0.64, 1.45) | 88.22 | (0.22, 4.19) | NA | 1.09 (0.92, 1.21) | No | Very low |
 Metabolic syndrome | 4 | 16,184 | OR | 1.31 (1.17, 1.47) | 24.73 | (0.93, 1.85) | NA | 1.38 (1.21, 1.57) | No | Very low |
Mortality | ||||||||||
 Overall | 4 | 82,497 | aHR | 1.47 (1.23, 1.76) | 65.73 | (0.84, 2.58) | NA | 1.30 (0.98, 1.73) | No | Very low |
 Cardiovascular disease | 3 | 49,503 | aHR | 1.23 (1.01, 1.50) | 0 | (0.33, 4.56) | NA | 1.10 (0.50, 1.42) | Yes | Low |
 Cancers | 4 | 92,104 | aHR | 2.57 (2.10, 3.18) | 0 | (1.61, 4.10) | NA | 1.75 (0.95, 3.22) | No | Low |
Infertility and sperm parameters | ||||||||||
 Infertility | 3 | 849 | OR | 1.67 (1.05, 2.65) | 0 | (0.07, 36.80) | NA | 4.22 (1.04, 17.14) | Yes | Very low |
 Semen volume | 5 | 890 | SMD |  − 0.50 (− 1.29, 0.26) | 94.79 | (− 3.41, 2.41) | NA |  − 1.90 (− 2.09, − 1.71) | No | Very low |
 Sperm active progressive motility | 5 | 1403 | SMD | 0.33 (− 3.04, 3.70) | 99.74 | (− 13.06, 13.73) | NA |  − 3.72 (− 3.99, − 3.46) | No | Very low |
 Sperm count | 6 | 1014 | SMD | 0.26 (− 1.13, 1.65) | 98.65 | (− 8.22, 5.96) | NA | 3.60 (3.29, 3.91) | No | Very low |
 Sperm DNA fragmentation | 3 | 712 | SMD | 3.36 (0.29, 6.43) | 98.98 | (− 36.28, 42.99) | NA | 6.43 (6.07, 6.83) | Yes | Very low |
 Sperm immotile | 4 | 871 | SMD | 1.24 (− 0.52, 3.01) | 98.88 | (− 7.36, 9.84) | NA | 0.36 (− 0.08, 0.80) | No | Very low |
 Sperm total motility | 3 | 767 | SMD |  − 1.58 (− 3.88, 0.72) | 99.10 | (− 31.28, 28.12) | NA |  − 3.88 (− 4.15, − 3.61) | No | Very low |
 Sperm nonprogressive motility | 3 | 767 | SMD | 0.01 (− 0.46, 0.49) | 83.28 | (− 5.70, 5.72) | NA |  − 0.38 (− 0.54, − 0.22) | No | Very low |
 Sperm normal form (NL morphology) | 6 | 1509 | SMD |  − 0.71 (− 1.33, − 0.10) | 95.66 | (− 2.91, 1.49) | NA |  − 1.51 (− 1.69, − 1.33) | No | Very low |
Respiratory symptoms and disease | ||||||||||
 Asthma | 4 | 71,081 | OR | 1.01 (0.39, 2.62) | 82.92 | (0.01, 69.10) | NA | 1.53 (1.41, 1.65) | Yes | Very low |
 COPD | 5 | 2627 | OR | 1.97 (0.88, 4.39) | 79.70 | (0.11, 34.55) | NA | 2.03 (0.95, 4.33) | Yes | Very low |
 Chronic bronchitis | 5 | 63,104 | OR | 3.61 (1.02, 12.72) | 96.46 | (0.03, 456.53) | NA | 1.31 (1.03, 1.66) | Yes | Very low |
 Cough | 4 | 61,584 | OR | 2.37 (1.17, 4.83) | 93.02 | (0.19, 29.51) | NA | 1.25 (1.06, 1.47) | Yes | Very low |
 Dyspnea | 3 | 61,250 | OR | 1.82 (0.58, 5.75) | 94.73 | NA | NA | 1.16 (1.02, 1.32) | Yes | Very low |
 Sputum | 3 | 61,730 | OR | 3.17 (1.49, 6.72) | 54.53 | NA | NA | 1.99 (1.14, 3.47) | No | Very low |
 Wheeze | 5 | 1844 | OR | 1.92 (0.82, 4.47) | 85.52 | (0.09, 41.59) | NA | 0.46 (0.26, 0.82) | Yes | Very low |
Spirometry parameters | ||||||||||
 FEV1 (predicted) | 14 | 3367 | SMD |  − 0.35 (− 0.59, − 0.10) | 90.17 | (− 1.33, 0.63) | Yes |  − 0.04 (0.19, 0.11) | No | Very low |
 FEV1 (volume) | 7 | 2007 | SMD |  − 0.31 (− 1.02, 0.39) | 97.93 | (− 2.87, 2.25) | NA | 0.98 (0.82, 1.13) | No | Very low |
 FVC (predicted) | 12 | 2825 | SMD |  − 0.18 (− 0.53, 0.17) | 94.77 | (− 1.55, 1.19) | No |  − 0.03 (− 0.18, 0.12) | No | Very low |
 FVC (volume) | 7 | 2007 | SMD | 0.08 (− 0.32, 0.48) | 93.90 | (− 0.57, 2.17) | NA | 1.05 (0.89, 1.21) | No | Very low |
 FEV1 on FVC fraction (observed) | 6 | 1411 | SMD |  − 0.10 (− 0.40, 0.20) | 81.23 | (− 1.07, 0.87) | NA |  − 0.18 (− 0.33, − 0.03) | No | Very low |
 FEV1 on FVC fraction (predicted) | 9 | 2294 | SMD |  − 0.58 (− 1.03, − 0.13) | 95.57 | (− 2.26, 1.10) | NA |  − 2.09 (− 2.31, − 1.87) | No | Very low |
 PEF (predicted) | 8 | 2093 | SMD |  − 0.38 (− 0.48, 0.08) | 95.69 | (− 2.04, 1.28) | NA | 0.41 (0.26, 0.56) | Yes | Very low |
 PEF (volume) | 4 | 1678 | SMD | 0.08 (− 0.61, 0.78) | 97.78 | (− 3.30, 3.46) | NA | 1.10 (0.94, 1.26) | Yes | Very low |
 FEF25–75 (predicted) | 6 | 1506 | SMD |  − 0.17 (− 0.49, 0.16) | 86.84 | (− 1.25, 0.99) | NA | 0.01 (− 0.15, 0.15) | No | Very low |
 FEF25–75 (volume) | 3 | 1378 | SMD |  − 0.63 (− 0.44, 1.70) | 98.67 | (− 19.85, 18.59) | NA | 0.01 (− 0.15, − 0.15) | No | Very low |
Neonatal anthropometry | ||||||||||
 Birth weight | 5 | 11,672 | SMD |  − 0.51 (− 0.83, − 0.18) | 93.55 | (− 1.84, 0.82) | NA |  − 0.04 (− 0.14, 0.07) | No | Low |
 Low birth weight | 3 | 8802 | OR | 1.53 (0.92, 2.55) | 63.08 | (0.01, 417.84) | NA | 1.05 (0.73, 1.49) | Yes | Very low |
Periodontal parameters | ||||||||||
 PI | 18 | 1638 | SMD | 3.25 (1.86, 4.65) | 98.94 | (− 3.43, 9.93) | No |  − 0.18 (− 0.73, 0.38) | No | Very low |
 Probing depth | 16 | 1277 | SMD | 3.46 (2.02, 4.89) | 98.54 | (− 2.94, 9.86) | Yes | 0.22 (− 0.34, 0.77) | No | Very low |
 Probing depth > 4 mm | 4 | 419 | SMD | 4.24 (2.30, 6.19) | 96.95 | (− 5.97, 14.49) | NA | 0.22 (− 0.34, 0.77) | No | Very low |
 Clinical attachment loss | 7 | 675 | SMD | 3.12 (1.03, 5.22) | 98.23 | (− 4.57, 10.81) | NA | 0.65 (0.09, 1.21) | Yes | Very low |
 Gingival index | 5 | 469 | SMD | 10.21 (− 11.23, 31.64) | 99.99 | (− 74.70, 95.12) | NA | 0.34 (0.03, 0.66) | No | Very low |
 BOP | 14 | 1237 | SMD |  − 3.23 (− 5.32, − 1.14) | 99.21 | (− 12.17, 5.71) | Yes |  − 0.38 (− 0.40, 0.18) | No | Very low |
 Distal MBL | 7 | 487 | SMD | 7.92 (3.59, 12.24) | 99.35 | (− 7.97, 23.81) | NA | 1.51 (1.03, 1.99) | No | Very low |
 Total distal CBL | 4 | 282 | SMD | 7.39 (3.99, 13.83) | 99.04 | (− 15.32, 30.10) | NA | 11.64 (9.80, 13.47) | Yes | Very low |
 Total mesial CBL | 4 | 282 | SMD | 6.47 (1.23, 11.71) | 99.11 | (− 14.21, 27.15) | NA | 15.78 (13.33, 18.24) | Yes | Very low |
 MBL | 3 | 298 | SMD | 2.74 (0.67, 4.80) | 97.42 | (− 23.86, 29.24) | NA | 3.32 (2.82, 3.83) | Yes | Very low |
 Mesial MBL | 7 | 487 | SMD | 7.94 (3.81, 12.08) | 99.22 | (− 7.25, 23.13) | NA | 1.97 (1.45, 2.49) | No | Very low |
Infectious disease | ||||||||||
 Hepatitis C | 3 | 8946 | aOR | 1.05 (0.79, 1.38) | 0 | (0.22, 5.29) | NA | 0.90 (0.40, 2.01) | No | Very low |