Table 3.
Subgroup and sensitivity analyses
| Highest vs. lowest consumption | Each 1 cup/d increment | |||||||
|---|---|---|---|---|---|---|---|---|
| N | RR (95% CI) | I2 (%) | P-diff | N | RR (95% CI) | I2 (%) | P-diff | |
| Subgroup analyses | ||||||||
| Geographic region | ||||||||
| US | 7 | 1.10 (0.92–1.32) | 50.4 | Ref. | 7 | 1.01 (0.97–1.04) | 70.0 | Ref. |
| Europe | 6 | 1.13 (0.98–1.31) | 0 | 0.60 | 5 | 1.02 (0.99–1.04) | 0 | 0.55 |
| Japan | 3 | 0.81 (0.57–1.16) | 23.1 | 0.23 | 3 | 0.92 (0.75–1.14) | 65.3 | 0.30 |
| Duration of follow-up | ||||||||
| ≥ 10 yr | 12 | 1.08 (0.95–1.23) | 35.9 | 11 | 1.01 (0.98–1.04) | 62.6 | ||
| < 10 yr | 4 | 1.04 (0.81–1.35) | 31.4 | 0.86 | 4 | 1.00 (0.95–1.04) | 42.3 | 0.67 |
| No. of participants | ||||||||
| ≥ 50,000 | 8 | 1.02 (0.91–1.15) | 28.9 | 8 | 1.00 (0.98–1.03) | 61.1 | ||
| < 50,000 | 8 | 1.21 (0.96–1.51) | 28.9 | 0.26 | 7 | 1.04 (0.97–1.13) | 52.0 | 0.67 |
| Sex | ||||||||
| Men | 10 | 1.16 (1.00–1.35) | 21.5 | 9 | 1.01 (0.98–1.05) | 42.0 | ||
| Women | 7 | 0.90 (0.59–1.37) | 63.6 | 0.37 | 6 | 0.98 (0.89–1.08) | 56.0 | 0.76 |
| No. of cases | ||||||||
| ≥ 200 | 10 | 1.02 (0.92–1.13) | 19.0 | 10 | 1.00 (0.98–1.02) | 57.3 | ||
| < 200 | 6 | 1.38 (1.05–1.81) | 12.0 | 0.064 | 5 | 1.12 (1.04–1.21) | 0 | 0.037 |
| % Male cases | ||||||||
| ≥ 75% | 6 | 1.10 (0.95–1.26) | 4.1 | 6 | 1.02 (0.94–1.10) | 69.3 | ||
| < 75% | 9 | 1.10 (0.92–1.30) | 37.6 | 0.98 | 7 | 1.01 (0.99–1.04) | 18.5 | 0.87 |
| % Current smoker | ||||||||
| ≥ 25% | 8 | 1.02 (0.82–1.25) | 26.3 | 7 | 1.00 (0.94–1.07) | 52.6 | ||
| < 25% | 8 | 1.10 (0.96–1.26) | 40.5 | 0.60 | 8 | 1.01 (0.98–1.03) | 63.6 | 0.98 |
| Smoking status | ||||||||
| Never | 6 | 1.15 (0.79–1.67) | 56.5 | Ref. | 6 | 1.02 (0.95–1.09) | 58.0 | Ref. |
| Former | 3 | 1.18 (0.92–1.52) | 55.5 | 0.80 | 3 | 1.01 (0.97–1.05) | 69.7 | 0.99 |
| Never/former | 6 | 1.20 (0.93–1.56) | 61.7 | 0.71 | 6 | 1.03 (0.98–1.08) | 76.3 | 0.80 |
| Current | 3 | 1.19 (0.97–1.46) | 0 | 0.72 | 3 | 1.04 (1.01–1.07) | 0 | 0.50 |
| Former/current | 4 | 1.12 (0.88–1.43) | 33.3 | 0.81 | 4 | 1.01 (0.95–1.07) | 38.4 | 0.73 |
| Statistical adjustment | ||||||||
| Smokinga | ||||||||
| Poorer | 3 | 1.48 (1.14–1.93) | 0 | Ref. | 3 | 1.08 (1.02–1.15) | 8.9 | Ref. |
| Moderate | 8 | 1.00 (0.80–1.26) | 31.7 | 0.058 | 7 | 0.98 (0.90–1.07) | 60.5 | 0.17 |
| Better | 5 | 1.03 (0.93–1.13) | 0 | 0.042 | 5 | 1.00 (0.98–1.02) | 49.7 | 0.055 |
| Alcohol drinking | ||||||||
| No | 12 | 1.13 (1.01–1.26) | 10.4 | 11 | 1.02 (0.99–1.04) | 34.5 | ||
| Yes | 4 | 0.91 (0.74–1.13) | 34.2 | 0.067 | 4 | 0.98 (0.92–1.04) | 68.8 | 0.075 |
| Education | ||||||||
| No | 10 | 1.18 (1.00–1.40) | 19.6 | 9 | 1.03 (0.99–1.07) | 44.1 | ||
| Yes | 6 | 0.99 (0.87–1.13) | 31.5 | 0.14 | 6 | 0.99 (0.96–1.03) | 69.5 | 0.33 |
| Physical activity | ||||||||
| No | 13 | 1.10 (0.95–1.29) | 33.4 | 12 | 1.01 (0.97–1.05) | 53.6 | ||
| Yes | 3 | 1.02 (0.88–1.17) | 24.4 | 0.48 | 3 | 1.00 (0.97–1.04) | 75.7 | 0.90 |
| BMI | ||||||||
| No | 12 | 1.15 (1.02–1.29) | 5.1 | 12 | 1.02 (0.99–1.05) | 33.9 | ||
| Yes | 4 | 0.92 (0.74–1.14) | 52.9 | 0.099 | 3 | 0.98 (0.93–1.03) | 80.7 | 0.31 |
| Diabetes | ||||||||
| No | 13 | 1.10 (0.96–1.25) | 27.1 | 12 | 1.01 (0.98–1.04) | 43.2 | ||
| Yes | 3 | 0.97 (0.73–1.29) | 60.4 | 0.57 | 3 | 0.99 (0.92–1.05) | 78.4 | 0.78 |
| Family history of cancer | ||||||||
| No | 14 | 1.10 (0.96–1.27) | 27.9 | 13 | 1.01 (0.98–1.05) | 49.9 | ||
| Yes | 2 | 0.99 (0.82–1.21) | 57.6 | 0.41 | 2 | 1.00 (0.96–1.04) | 87.0 | 0.74 |
| Energy intake | ||||||||
| No | 14 | 1.08 (0.96–1.23) | 35.3 | 13 | 1.01 (0.99–1.04) | 59.0 | ||
| Yes | 2 | 1.00 (0.74–1.36) | 28.9 | 0.74 | 2 | 0.98 (0.91–1.04) | 51.3 | 0.43 |
| Fruit/vegetable consumption | ||||||||
| No | 12 | 1.13 (0.97–1.33) | 32.1 | 11 | 1.02 (0.98–1.06) | 51.5 | ||
| Yes | 4 | 1.00 (0.88–1.14) | 16.5 | 0.29 | 4 | 1.00 (0.97–1.03) | 72.1 | 0.54 |
| Tea consumption | ||||||||
| No | 11 | 1.15 (1.02–1.29) | 11.4 | 10 | 1.02 (0.99–1.05) | 40.8 | ||
| Yes | 5 | 0.92 (0.96–1.20) | 12.3 | 0.042 | 5 | 0.99 (0.96–1.03) | 62.1 | 0.26 |
| Sensitivity analysis | ||||||||
| Excluding 1 studyb | 15 | 1.10 (0.98–1.23) | 22.4 | 14 | 1.01 (0.99–1.04) | 47.0 | ||
| Excluding 2 studiesc | 14 | 1.10 (0.97–1.25) | 27.9 | 13 | 1.01 (0.98–1.04) | 51.0 | ||
“N” indicates the number of studies included in the analyses; “P-diff” indicates P values for differences between subgroup population (derived using meta-regression analyses)
a Poorer adjustment for smoking: no adjustment for smoking or adjustment for smoking status only; moderate adjustment for smoking: adjustment for smoking status in addition smoking frequency (e.g. cigarettes smoked per day, or pack-years of smoking) either continuously or categorically; better adjustment for smoking: adjustment for smoking status, smoking frequency, in addition to smoking duration or lifetime smoking intensity. One study (Gaspstur, 2017) that reported results only for nonsmokers (never and former smokers) and adjusted for smoking history for former smokers was included in the “better” group. Another study (Hashemian, 2019) that included totally current smokers and adjusted for both smoking frequency and duration was included in the “moderate group” (this study further examined coffee-bladder cancer association by smoking frequency and did not find group differences in the association)
b Excluding one study (Gaspstur, 2017) in which the study outcome was bladder cancer mortality, and all analyzed participants were never or former smokers
c In addition to the above-mentioned study (Gaspstur, 2017), further excluding another study (Hashemian, 2019) in which all participants were current smokers