Table 2. Summary relative risks (95% confidence intervals) of high vs. low levels of dietary nitrate intake in relation to cancer risk, stratified by selected study characteristics.
| Variable | Colorectal cancer | Gastric cancer | Esophageal cancer | |||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Number of RRs | RR (95%CI) | Ph* | Ph† | Number of RRs | RR (95%CI) | Ph* | Ph† | Number of RRs | RR (95%CI) | Ph* | Ph† | |
| Sex | 0.820 | 0.167 | 0.783 | |||||||||
| Male | - | - | - | 1 | 1.04(0.74-1.44) | 0.913 | 1 | 1.05 (0.61-1.83) | 0.471 | |||
| Female | 1 | 1.08 (0.73-1.59) | - | 1 | 0.85(0.49-1.46) | 0.407 | 1 | 0.53 (0.20-1.37) | 0.306 | |||
| Male and female | 5 | 1.07 (0.97-1.18) | 0.335 | 14 | 0.75(0.63-0.88) | 0.030 | 3 | 0.95 (0.72-1.25) | 0.080 | |||
| Study design | 0.105 | 0.002 | 0.073 | |||||||||
| HC-CS | - | - | - | 4 | 0.53(0.42-0.68) | 0.115 | - | - | - | |||
| PC-CS | 2 | 0.90 (0.74-1.10) | 0.324 | 5 | 0.69(0.59-0.81) | 0.144 | 2 | 0.55 (0.32-0.94) | 0.297 | |||
| CS | 4 | 1.12 (1.01-1.25) | 0.915 | 6 | 0.92(0.78-1.09) | 0.866 | 2 | 1.06 (0.82-1.39) | 0.533 | |||
| Study populations | 0.817 | 0.739 | 0.929 | |||||||||
| Asians | 1 | 1.08 (0.73-1.59) | - | 1 | 1.13(0.42-3.05) | - | - | - | - | |||
| Americans | 4 | 1.07 (0.97-1.18) | 0.232 | 5 | 0.75(0.65-0.87) | 0.120 | 3 | 0.95 (0.72-1.25) | 0.080 | |||
| Europeans | 1 | 1.04 (0.54-2.02) | - | 8 | 0.77(0.61-0.98) | 0.018 | 1 | 0.89 (0.55-1.43) | 0.379 | |||
| Cancer subtypes | 0.310 | 0.710 | 0.539 | |||||||||
| Colon/GCA/EA | 2 | 0.90 (0.70-1.15) | 0.200 | 2 | 0.90(0.64-1.27) | 0.644 | 2 | 1.00 (0.73-1.38) | 0.244 | |||
| Rectum/GNCA/ESCC | 2 | 1.09 (0.80-1.48) | 0.913 | 2 | 0.99(0.76-1.28) | 0.672 | 2 | 1.22 (0.76-1.97) | 0.656 | |||
| Adjustments in models | ||||||||||||
| Body mass index | 0.578 | 0.780 | 0.854 | |||||||||
| No | 4 | 0.99 (0.84-1.18) | 0.735 | 11 | 0.74(0.65-0.86) | 0.413 | 1 | 0.80 (0.30-1.80) | - | |||
| Yes | 2 | 1.10 (0.98-1.24) | 0.080 | 4 | 0.78(0.59-1.04) | 0.004 | 3 | 0.95 (0.74-1.21) | 0.134 | |||
| Total energy intake | 0.416 | 0.878 | - | |||||||||
| No | 1 | 0.92 (0.69-1.23) | 0.135 | 7 | 0.73(0.63-0.85) | 0.357 | - | - | - | |||
| Yes | 5 | 1.09 (0.98-1.20) | 0.629 | 8 | 0.79(0.62-0.99) | 0.011 | 4 | 0.94 (0.74-1.19) | 0.194 | |||
| Cigarette smoking | 0.567 | 0.022 | ||||||||||
| No | 3 | 0.99 (0.83-1.18) | 0.600 | 8 | 0.67(0.54-0.84) | 0.050 | - | - | - | - | ||
| Yes | 3 | 1.10 (0.98-1.24) | 0.213 | 7 | 0.91(0.77-1.07) | 0.770 | 4 | 0.94 (0.74-1.19) | 0.194 | |||
| Alcohol consumption | 0.260 | 0.055 | ||||||||||
| No | 5 | 1.10 (0.99-1.21) | 0.565 | 9 | 0.68(0.55-0.85) | 0.063 | - | - | - | - | ||
| Yes | 1 | 0.89 (0.68-1.16) | - | 6 | 0.89(0.76-1.05) | 0.575 | 4 | 0.94 (0.74-1.19) | 0.194 | |||
| Vitamin C intake | 0.820 | 0.336 | 0.854 | |||||||||
| No | 5 | 1.07 (0.97-1.18) | 0.335 | 13 | 0.76(0.65-0.89) | 0.036 | 3 | 0.95 (0.74-1.21) | 0.134 | |||
| Yes | 1 | 1.08 (0.73-1.59) | - | 2 | 0.98(0.63-1.54) | 0.165 | 1 | 0.80 (0.30-1.80) | - | |||
| Physical activity | 0.412 | 0.061 | 0.073 | |||||||||
| No | 4 | 1.10 (0.99-1.22) | 0.437 | 13 | 0.72(0.60-0.86) | 0.052 | 2 | 0.55 (0.32-0.94) | 0.297 | |||
| Yes | 2 | 0.95 (0.76-1.18) | 0.422 | 2 | 0.872 | 2 | 1.06 (0.82-1.39) | 0.533 | ||||
| Family history of cancer | - | 0.033 | - | |||||||||
| No | 6 | 1.07 (0.97-1.17) | 0.444 | 11 | 0.80(0.71-0.90) | 0.340 | 4 | 0.94 (0.74-1.19) | 0.194 | |||
| Yes | - | - | - | 4 | 0.61(0.42-0.87) | 0.087 | - | - | - | |||
*
P value for heterogeneity within each subgroup.
†
P value for heterogeneity between subgroups with meta-regression analysis.