TABLE 2.
The results and the level of evidence of the effect of tea and risk of cancer1
| Outcome | Study type | Comparison | Type of tea | P value (random-effects)2 | 95% PI including null | Heterogeneity (I2)2 | Effect-size distribution (D/N/I)3 | Small study effect4 | Concordance | Metrics | Summary effect (random-effects)5 |
|---|---|---|---|---|---|---|---|---|---|---|---|
| Associations supported by convincing evidence | |||||||||||
| Oral cancer | CC | Any vs. none | Any tea | <10−6 | No | Not large | 6/0/0 | No | Yes | OR | 0.62 (0.55, 0.72) |
| Associations supported by suggestive evidence | |||||||||||
| Biliary tract cancer | Obs | Any vs. none | Any tea | <0.05 but >10−6 | Yes | Not large | 4/4/0 | No | Yes | RR | 0.77 (0.64, 0.92) |
| Breast cancer | CC | High vs. low | Green tea | <0.05 but >10−6 | Yes | Large6 | 6/5/0 | No | Yes | RR | 0.75 (0.61, 0.92) |
| Endometrial cancer | Obs | High vs. low | Green tea | <0.05 but >10−6 | Yes | Not large | 2/4/0 | No | Yes | RR | 0.78 (0.61, 1.00)7 |
| Liver cancer | Obs | High vs. low | Green tea | <0.05 but >10−6 | Yes | Not large | 2/9/0 | No | No | RR | 0.87 (0.78, 0.98) |
| Oral cancer | Obs | High vs. low | Green tea | <0.05 but >10−6 | Yes | Not large | 1/4/0 | No | No | RR | 0.82 (0.69, 0.96) |
| Oral cancer | Obs | High vs. low | Any tea | <0.05 but >10−6 | No | Not large | 5/26/0 | No | Yes | RR | 0.86 (0.80, 0.91) |
| Associations supported by weak evidence | |||||||||||
| Breast cancer | Obs | High vs. low | Green tea | <0.05 but >10−6 | Yes | Large | 6/10/0 | No | No | RR | 0.82 (0.71, 0.96) |
| Breast cancer | Obs | Any vs. none | Green tea | <0.05 but >10−6 | Yes | Large | 3/11/0 | No | Yes | OR | 0.87 (0.76, 0.99) |
| Breast cancer | Obs | Any vs. none | Any tea | <0.05 but >10−6 | Yes | Very large | 6/20/0 | No | No | RR | 0.81 (0.71, 0.94) |
| Colorectal cancer | Obs | High vs. low | Any tea | <0.05 but >10−6 | Yes | Not large | 6/45/2 | Yes | No | RR | 0.93 (0.87, 0.99) |
| Colorectal cancer | Obs | High vs. low | Green tea | <0.05 but >10−6 | Yes | Large | 4/11/0 | No | No | RR | 0.87 (0.75, 1.00)7 |
| Gastric cancer | Obs | Any vs. none | Any tea | <0.001 | Yes | Very large | 23/30/3 | Yes | No | RR | 0.78 (0.70, 0.86) |
| Leukemia | Obs | High vs. low | Any tea | <0.001 | No | Not large | 4/4/0 | Yes | No | RR | 0.55 (0.43, 0.72) |
| Leukemia | Obs | Any vs. none | Any tea | <0.05 but >10−6 | No | Not large | 1/7/0 | Yes | No | RR | 0.76 (0.65, 0.89) |
| Liver cancer | Obs | Any vs. none | Green tea | <0.05 but >10−6 | Yes | Large | 3/7/0 | No | No | RR | 0.65 (0.48, 0.88) |
| Lung cancer | Obs | Any vs. none | Any tea | <0.001 | Yes | Very large | 18/24/1 | No | Yes | RR | 0.76 (0.67, 0.86) |
| Ovarian cancer | Obs | Any vs. none | Any tea | <0.05 but >10−6 | Yes | Very large | 8/22/1 | No | No | RR | 0.82 (0.71, 0.94) |
| Thyroid cancer | Obs | High vs. low | Any tea | <0.05 but >10−6 | Yes | Not large | 1/13/0 | Yes | No | RR | 0.77 (0.61, 0.97) |
| Nonsignificant associations | |||||||||||
| Acute leukemia (childhood) | Obs | High vs. low | Any tea | >0.05 | Yes | Not large | 0/8/1 | No | Yes | RR | 0.93 (0.74, 1.18) |
| Acute leukemia (childhood) | Obs | Any vs. none | Any tea | >0.05 | Yes | Not large | 0/14/0 | No | No | RR | 0.93 (0.82, 1.05) |
| Bladder cancer | CC | High vs. low | Any tea | >0.05 | Yes | Large | 1/22/2 | No | Yes | RR | 0.97 (0.87, 1.09) |
| Bladder cancer | Obs | High vs. low | Any tea | >0.05 | Yes | Large | 2/29/2 | No | Yes | RR | 0.95 (0.86, 1.06) |
| Bladder cancer | Co | High vs. low | Any tea | >0.05 | Yes | Large | 1/7/0 | No | Yes | RR | 0.86 (0.65, 1.13) |
| Bladder cancer | Obs | High vs. low | Green tea | >0.05 | Yes | Not large | 0/5/0 | No | Yes | RR | 1.03 (0.82, 1.31) |
| Brain cancer | Obs | Any vs. none | Any tea | >0.05 | Yes | Not large | 2/6/0 | No | No | RR | 0.90 (0.74, 1.09) |
| Breast cancer | Co | High vs. low | Black tea | >0.05 | Yes | Not large | 0/15/0 | No | No | RR | 1.04 (0.97, 1.12) |
| Breast cancer | CC | High vs. low | Black tea | >0.05 | Yes | Large | 1/12/0 | No | No | RR | 0.91 (0.80, 1.03) |
| Breast cancer | Obs | High vs. low | Black tea | >0.05 | Yes | Large | 1/27/0 | No | Yes | RR | 0.98 (0.91, 1.06) |
| Breast cancer | Co | High vs. low | Green tea | >0.05 | Yes | Not large | 0/5/0 | No | Yes | RR | 0.99 (0.83, 1.77) |
| Breast cancer | Co | Any vs. none | Green tea | >0.05 | Yes | Not large | 0/9/0 | No | Yes | OR | 0.94 (0.83, 1.05) |
| Breast cancer | CC | Any vs. none | Green tea | >0.05 | Yes | Very large | 3/2/0 | No | No | OR | 0.83 (0.62, 1.10) |
| Breast cancer | Co | High vs. low | Any tea | >0.05 | Yes | Not large | 0/12/2 | No | Yes | RR | 1.03 (0.96, 1.10) |
| Breast cancer | CC | High vs. low | Any tea | >0.05 | Yes | Large | 1/8/0 | No | Yes | OR | 0.90 (0.75, 1.10) |
| Breast cancer | Obs | High vs. low | Any tea | >0.05 | Yes | Large | 1/20/2 | No | Yes | RR | 0.98 (0.90, 1.06) |
| Colon cancer | Obs | High vs. low | Green tea | >0.05 | Yes | Not large | 1/9/1 | Yes | Yes | RR | 0.98 (0.85, 1.12) |
| Colorectal cancer | Obs | High vs. low | Black tea | >0.05 | Yes | Large | 2/14/4 | No | Yes | RR | 0.99 (0.87, 1.13) |
| Endometrial cancer | Obs | High vs. low | Any tea | >0.05 | Yes | Large | 3/12/1 | Yes | Yes | RR | 0.90 (0.75, 1.09) |
| Endometrial cancer | Obs | Increment of 1cup/d | Any tea | >0.05 | Yes | Large | 0/4/1 | No | Yes | RR | 1.04 (0.98, 1.10) |
| Endometrial cancer | Obs | High vs. low | Green tea | >0.05 | Yes | Large | 1/8/1 | No | No | RR | 0.99 (0.79, 1.23) |
| Esophageal cancer | Obs | High vs. low | Green tea | >0.05 | Yes | Large | 9/11/2 | No | Yes | RR | 0.81 (0.62, 1.06) |
| Gallbladder cancer | Obs | High vs. low | Any tea | >0.05 | Yes | Very large | 2/2/0 | No | No | RR | 0.57 (0.25, 1.30) |
| Gallbladder cancer | Obs | Any vs. none | Any tea | >0.05 | Yes | Very large | 3/3/0 | No | No | RR | 0.67 (0.40, 1.12) |
| Gastric cancer | Obs | High vs. low | Green tea | >0.05 | Yes | Large | 3/25/2 | Yes | Yes | RR | 0.93 (0.84, 1.04) |
| Gastric cancer | Obs | High vs. low | Black tea | >0.05 | Yes | Not large | 0/4/1 | No | Yes | RR | 1.18 (0.79, 1.77) |
| Gastric cancer | Obs | Increment of 3cups/d | Any tea | >0.05 | Yes | Not large | 0/5/0 | No | Yes | RR | 0.98 (0.89, 1.08) |
| Glioma | Obs | Any vs. none | Any tea | >0.05 | Yes | Very large | 0/4/0 | No | No | RR | 0.67 (0.40, 1.12) |
| Glioma | Obs | High vs. low | Any tea | >0.05 | Yes | Very large | 1/3/0 | No | No | RR | 0.57 (0.25, 1.30) |
| Laryngeal cancer | Obs | High vs. low | Any tea | >0.05 | Yes | Large | 2/5/1 | No | Yes | RR | 0.91 (0.67, 1.23) |
| Liver cancer | Obs | Any vs. none | Any tea | >0.05 | Yes | Very large | 3/9/0 | No | No | RR | 0.77 (0.57, 1.03) |
| Lung cancer | Obs | High vs. low | Green tea | >0.05 | Yes | Very large | 4/7/1 | No | Yes | RR | 0.78 (0.61, 1.01) |
| Lung cancer | Obs | High vs. low | Black tea | >0.05 | Yes | Large | 4/10/0 | No | Yes | RR | 0.86 (0.70, 1.05) |
| Oropharyngeal cancer | Obs | Any vs. none | Any tea | >0.05 | Yes | Large | 2/4/0 | No | Yes | RR | 0.68 (0.45, 1.03) |
| Ovarian cancer | Obs | Any vs. none | Green tea | >0.05 | Yes | Very large | 3/5/1 | No | Yes | RR | 0.76 (0.57, 1.02) |
| Ovarian cancer | Obs | Any vs. none | Black tea | >0.05 | Yes | Large | 4/12/0 | Yes | Yes | RR | 0.90 (0.78, 1.04) |
| Pancreatic cancer | Obs | High vs. low | Any tea | >0.05 | Yes | Not large | 1/20/1 | No | Yes | RR | 0.97 (0.85, 1.10) |
| Pancreatic cancer | Obs | Any vs. none | Any tea | >0.05 | Yes | Large | 2/25/2 | No | Yes | RR | 0.99 (0.89, 1.10) |
| Pancreatic cancer | Obs | High vs. low | Green tea | >0.05 | Yes | Large | 1/6/1 | No | Yes | RR | 0.99 (0.78, 1.25) |
| Pharyngeal cancer | Obs | Any vs. none | Any tea | >0.05 | Yes | Not large | 0/4/0 | No | Yes | RR | 0.88 (0.74, 1.04) |
| Prostate cancer | Obs | High vs. low | Green tea | >0.05 | Yes | Very large | 3/6/0 | Yes | Yes | RR | 0.73 (0.51, 1.06) |
| Prostate cancer | Obs | High vs. low | Any tea | >0.05 | Yes | Large | 6/15/2 | Yes | Yes | RR | 0.86 (0.71, 1.04) |
| Prostate cancer | Obs | Any vs. none | Any tea | >0.05 | Yes | Large | 7/20/2 | Yes | Yes | RR | 0.87 (0.75, 1.01) |
| Prostate cancer | Obs | High vs. low | Black tea | >0.05 | Yes | Not large | 1/9/1 | No | Yes | RR | 0.99 (0.82, 1.20) |
| Rectal cancer | Obs | High vs. low | Green tea | >0.05 | Yes | Large | 3/6/0 | No | Yes | RR | 0.97 (0.77, 1.22) |
| Renal cell carcinoma | Obs | Any vs. none | Any tea | >0.05 | Yes | Very large | 1/11/0 | No | Yes | RR | 1.03 (0.88, 1.21) |
| Skin cancer (non-melanoma) | Obs | Any vs. none | Any tea | >0.05 | Yes | Not large | 4/4/0 | No | Yes | OR | 0.88 (0.76, 1.02) |
1
CC, case-control studies; Co, cohort studies; Obs, observational studies; PI, prediction interval.
2
Heterogeneity is defined as “Very large” when I2 > 75%, “Large” when 50% < I2 < 75%, and “Not large” when I2 < 50%.
3
Number of individual studies of effect size with statistical significance in direction of decreased cancer risk(D)/no association(N)/increased cancer risk(I).
4
The presence of small study effects is determined if the Egger P value is <0.10.
5
Summary effect with 95% CI value obtained from umbrella review combining meta-analyses of the same comparison.
6
Although heterogeneity is large, the distribution of the effect sizes was considered over the I2 metrics.
7
The value is rounded up (to 2 decimal places), and hence is statistically significant.