Table 2.
Subgroup analyses of smoking and gallbladder disease
| Current smoking | Former smoking | Ever smoking | |||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| n | Relative risk (95 % CI) | I 2 (%) | P ah | P 2h | n | Relative risk (95 % CI) | I 2 (%) | P ah | P bh | n | Relative risk (95 % CI) | I 2 (%) | P ah | P bh | |
| All studies | 6 | 1.19 (1.12–1.28) | 46.9 | 0.09 | 6 | 1.10 (1.07–1.13) | 0 | 0.88 | 7 | 1.15 (1.13–1.18) | 0 | 0.43 | |||
| Follow-up | |||||||||||||||
| <10 years | 4 | 1.17 (1.09–1.26) | 56.1 | 0.08 | 0.20 | 4 | 1.10 (1.07–1.13) | 0 | 0.77 | 0.66 | 4 | 1.15 (1.12–1.18) | 0 | 0.48 | 0.22 |
| ≥10 years | 2 | 1.37 (1.15–1.64) | 0 | 0.50 | 2 | 1.16 (0.94–1.43) | 0 | 0.51 | 3 | 1.24 (1.12–1.37) | 0 | 0.45 | |||
| Gender | |||||||||||||||
| Men | 2 | 1.37 (1.15–1.64) | 0 | 0.50 | 0.05/0.18d | 2 | 1.16 (0.94–1.43) | 0 | 0.51 | 0.78/0.66d | 2 | 1.28 (1.10–1.48) | 15.9 | 0.28 | 0.21/0.25d |
| Women | 3 | 1.21 (1.18–1.25) | 0 | 0.49 | 3 | 1.10 (1.06–1.13) | 0 | 0.78 | 3 | 1.15 (1.13–1.18) | 0 | 0.55 | |||
| Men and women | 1 | 1.05 (0.94–1.19) | 1 | 1.18 (0.99–1.41) | 2 | 1.12 (1.03–1.21) | 0 | 0.35 | |||||||
| Study design | |||||||||||||||
| Cohort | 5 | 1.22 (1.18–1.25) | 0 | 0.45 | 0.08 | 5 | 1.10 (1.07–1.13) | 0 | 0.88 | 0.47 | 6 | 1.16 (1.13–1.19) | 0 | 0.48 | 0.28 |
| Nested case–control study | 1 | 1.05 (0.94–1.19) | 1 | 1.18 (0.99–1.41) | 1 | 1.09 (0.99–1.20) | |||||||||
| Outcometype | |||||||||||||||
| Gallbladder disease | 5 | 1.19 (1.10–1.28) | 56.1 | 0.06 | 0.52 | 5 | 1.21 (1.18–1.25) | 0 | 0.43 | 0.05 | 5 | 1.15 (1.10–1.20) | 29.3 | 0.23 | 0.65 |
| Gallstones | 2 | 1.16 (1.01–1.33) | 1.0 | 0.32 | 2 | 1.09 (0.93–1.29) | 0 | 0.96 | 3 | 1.15 (1.05–1.25) | 0 | 0.66 | |||
| Cholecystectomy | 1 | 1.27 (1.15–1.39) | 1 | 1.06 (0.94–1.18) | 1 | 1.18 (1.09–1.27) | |||||||||
| Geographic location | |||||||||||||||
| Europe | 2 | 1.14 (0.99–1.32) | 82.7 | 0.02 | 0.38 | 2 | 1.10 (1.07–1.14) | 0 | 0.44 | 0.67 | 2 | 1.14 (1.09–1.20) | 33.3 | 0.22 | 0.63 |
| America | 4 | 1.23 (1.12–1.36) | 17.4 | 0.30 | 4 | 1.08 (0.99–1.17) | 0 | 0.80 | 4 | 1.18 (1.08–1.28) | 30.1 | 0.23 | |||
| Asia | 0 | 0 | 1 | 1.19 (1.02–1.40) | |||||||||||
| Number of cases | |||||||||||||||
| Cases <1000 | 3 | 1.35 (1.17–1.56) | 0 | 0.75 | 0.17 | 3 | 1.14 (0.96–1.34) | 0 | 0.77 | 0.72 | 3 | 1.25 (1.12–1.40) | 0 | 0.49 | 0.21 |
| Cases ≥1000 | 3 | 1.16 (1.07–1.25) | 69.2 | 0.04 | 3 | 1.10 (1.07–1.13) | 0 | 0.57 | 4 | 1.15 (1.12–1.18) | 0 | 0.48 | |||
| Study quality | |||||||||||||||
| 0–3 stars | 0.55 | 0 | 0.65 | 0.83 | |||||||||||
| 4–6 stars | 3 | 1.24 (1.08–1.43) | 37.4 | 0.20 | 3 | 1.08 (0.98–1.18) | 0 | 0.61 | 4 | 1.18 (1.08–1.28) | 29.2 | 0.24 | |||
| 7–9 stars | 3 | 1.17 (1.05–1.31) | 67.5 | 0.05 | 3 | 1.10 (1.07–1.14) | 0 | 0.75 | 3 | 1.16 (1.13–1.18) | 0 | 0.43 | |||
| Adjustment for confounding factors c | |||||||||||||||
| Age | |||||||||||||||
| Yes | 6 | 1.19 (1.12–1.28) | 46.9 | 0.09 | NC | 6 | 1.10 (1.07–1.13) | 0 | 0.88 | NC | 7 | 1.15 (1.13–1.18) | 0 | 0.43 | NC |
| No | 0 | 0 | 0 | ||||||||||||
| Alcohol | |||||||||||||||
| Yes | 4 | 1.17 (1.09–1.26) | 56.1 | 0.08 | 0.20 | 3 | 1.10 (1.07–1.13) | 0 | 0.77 | 0.66 | 5 | 1.15 (1.13–1.18) | 0 | 0.62 | 0.20 |
| No | 2 | 1.37 (1.15–1.64) | 0 | 0.50 | 2 | 1.16 (0.94–1.43) | 0 | 0.51 | 2 | 1.28 (1.10–1.48) | 15.9 | 0.28 | |||
| BMI | |||||||||||||||
| Yes | 5 | 1.19 (1.10–1.28) | 55.6 | 0.06 | 0.59 | 5 | 1.10 (1.07–1.13) | 0 | 0.77 | 0.99 | 5 | 1.15 (1.10–1.20) | 28.8 | 0.23 | 0.61 |
| No | 1 | 1.30 (1.00–1.60) | 1 | 1.10 (0.90–1.50) | 2 | 1.19 (1.06–1.34) | 0 | 0.94 | |||||||
| Weight change or BMI change | |||||||||||||||
| Yes | 3 | 1.24 (1.08–1.43) | 37.4 | 0.20 | 0.55 | 3 | 1.08 (0.98–1.18) | 0 | 0.61 | 0.65 | 3 | 1.19 (1.06–1.35) | 50.4 | 0.13 | 0.83 |
| No | 3 | 1.17 (1.05–1.31) | 67.5 | 0.05 | 3 | 1.10 (1.07–1.14) | 0 | 0.75 | 4 | 1.16 (1.13–1.19) | 0 | 0.61 | |||
| Hormone replacement therapy | |||||||||||||||
| Yes | 2 | 1.17 (1.08–1.27) | 0 | 0.42 | 0.74 | 2 | 1.06 (0.97–1.17) | 0 | 0.81 | 0.56 | 2 | 1.13 (1.06–1.20) | 0 | 0.51 | 0.50 |
| No | 2 | 1.14 (0.99–1.32) | 82.7 | 0.02 | 2 | 1.10 (1.07–1.14) | 0 | 0.44 | 3 | 1.16 (1.13–1.18) | 0 | 0.44 | |||
| Oral contraceptive use | |||||||||||||||
| Yes | 1 | 1.30 (1.00–1.70) | 0.54 | 1 | 1.10 (0.80–1.40) | 0.99 | 1 | 1.20 (0.99–1.46) | 0.69 | ||||||
| No | 3 | 1.16 (1.07–1.25) | 69.2 | 0.04 | 3 | 1.10 (1.07–1.13) | 0 | 0.57 | 4 | 1.15 (1.12–1.18) | 0 | 0.48 | |||
| Parity | |||||||||||||||
| Yes | 2 | 1.17 (1.08–1.27) | 0 | 0.42 | 0.74 | 2 | 1.06 (0.97–1.17) | 0 | 0.81 | 0.56 | 2 | 1.13 (1.06–1.20) | 0 | 0.51 | 0.50 |
| No | 2 | 1.14 (0.99–1.32) | 82.7 | 0.02 | 2 | 1.10 (1.07–1.14) | 0 | 0.44 | 3 | 1.16 (1.13–1.18) | 0 | 0.44 | |||
| Physical activity | |||||||||||||||
| Yes | 1 | 1.47 (1.13–1.92) | 0.21 | 1 | 1.28 (0.89–1.85) | 0.46 | 1 | 1.40 (1.13–1.74) | 0.14 | ||||||
| No | 5 | 1.18 (1.11–1.26) | 44.9 | 0.12 | 5 | 1.10 (1.07–1.13) | 0 | 0.89 | 6 | 1.15 (1.13–1.18) | 0 | 0.72 | |||
n denotes the number of studies
aP for heterogeneity within each subgroup
bP for heterogeneity between subgroups with meta-regression analysis
cNumber of studies may not add up to the total because some studies did not report the information or the subgroup analysis may not apply to some studies (e.g. subgroup analyses of HRT, OC use and parity are restricted to studies including women)
dP for heterogeneity between men and women (excluding studies with both genders)