Table 2.
Association between average trihalomethane (THM) concentrations in residential tap water and colorectal cancer. Odds ratios (ORs) and 95% confidence intervals (CIs) among 1,837 cases and 3,454 controls.
| Exposure | All (n = 5,291) | Men (n = 2,977) | Women (n = 2,312)a | ||||||
|---|---|---|---|---|---|---|---|---|---|
| Cases | Controls | ORb (95% CI) | Cases | Controls | ORb (95% CI) | Cases | Controls | ORb (95% CI) | |
| Total THMs (μg/L) | |||||||||
| < 16.2 | 591 | 741 | 1 | 393 | 447 | 1 | 196 | 294 | 1 |
| 16.2–29.5 | 378 | 954 | 0.57 (0.45, 0.72) | 241 | 407 | 0.56 (0.41, 0.77) | 137 | 547 | 0.62 (0.41, 0.93) |
| 29.5–62 | 323 | 1,007 | 0.44 (0.33, 0.58) | 193 | 530 | 0.38 (0.27, 0.55) | 130 | 477 | 0.60 (0.38, 0.93) |
| > 62 | 545 | 752 | 0.92 (0.66, 1.28) | 349 | 417 | 1.04 (0.68, 1.60) | 196 | 335 | 0.68 (0.39, 1.20) |
| p-Trendc | 0.187 | 0.741 | 0.165 | ||||||
| Chloroform (μg/L) | |||||||||
| < 6 | 589 | 744 | 1 | 387 | 446 | 1 | 200 | 298 | 1 |
| 6–17.4 | 435 | 895 | 0.69 (0.55, 0.87) | 268 | 404 | 0.69 (0.51, 0.93) | 167 | 491 | 0.71 (0.49, 1.03) |
| 17.4–23.4 | 515 | 798 | 0.68 (0.53, 0.87) | 335 | 384 | 0.73 (0.53, 1.01) | 180 | 414 | 0.65 (0.43, 0.97) |
| > 23.4 | 298 | 1,017 | 0.31 (0.24, 0.41) | 186 | 567 | 0.26 (0.18, 0.37) | 112 | 450 | 0.46 (0.29, 0.72) |
| p-Trendc | < 0.001 | < 0.001 | 0.001 | ||||||
| Brominated THMs (μg/L) | |||||||||
| < 3.7 | 541 | 792 | 1 | 348 | 483 | 1 | 191 | 309 | 1 |
| 3.7–9.0 | 387 | 943 | 0.77 (0.60, 0.98) | 238 | 419 | 0.73 (0.53, 1.01) | 149 | 524 | 0.78 (0.52, 1.17) |
| 9.0–41.8 | 368 | 963 | 0.55 (0.38, 0.79) | 241 | 479 | 0.57 (0.36, 0.90) | 127 | 484 | 0.49 (0.26, 0.91) |
| > 41.8 | 541 | 756 | 1.00 (0.65, 1.53) | 349 | 420 | 1.43 (0.83, 2.46) | 192 | 336 | 0.44 (0.21, 0.92) |
| p-Trendc | 0.556 | 0.036 | 0.039 | ||||||
| aTwo female cases were excluded from the sex-stratified model because one category in education does not have observations among controls and was dropped from the model. bAdjusted for sex, age, area, education, nonsteroidal antiinflammatory drug consumption, smoking, physical activity, and family history of colorectal cancer. The analysis excludes subjects with poor or questionable interviews and with known THM concentrations for < 70% of the exposure window (from age 18 to 2 years before the interview). cLinear trend p-value, derived from a likelihood-ratio test comparing a model with the categorical nitrate variable as an ordinal variable (0, 1, 2), with a model that excluded the variable. | |||||||||