Table 3.
Association between drinking water nitrate-nitrogen (NO3-N) in public water supplies and bladder cancer in the Iowa Women’s Health Study, stratified by smoking status (n = 15,577).
| Drinking water nitrate | Never smokers | Former smokers | Current smokers | pinteractionb | ||||||
|---|---|---|---|---|---|---|---|---|---|---|
| Cases | n | HRa (95% CI) | Cases | n | HRa (95% CI) | Cases | n | HRa (95% CI) | ||
| Average NO3-N (mg/L) | ||||||||||
| < 0.47 | 17 | 2,499 | 1.00 (Reference) | 8 | 1,149 | 0.70 (0.28, 1.76) | 4 | 325 | 1.24 (0.37, 4.13) | |
| 0.47–1.07 | 13 | 2,393 | 0.81 (0.39, 1.67) | 16 | 1,142 | 1.43 (0.66, 3.14) | 3 | 318 | 1.00 (0.26, 3.78) | |
| 1.08–2.97 | 14 | 2,487 | 0.83 (0.41, 1.68) | 11 | 1,305 | 0.83 (0.35, 1.95) | 5 | 338 | 1.57 (0.51, 4.82) | |
| > 2.97 | 15 | 2,275 | 0.97 (0.49, 1.95) | 14 | 1,048 | 1.30 (0.58, 2.94) | 10 | 298 | 3.67 (1.43, 9.38) | 0.03 |
| Total | 59 | 9,654 | 49 | 4,644 | 22 | 1,279 | ||||
| Years > ½–MCL (> 5 mg/L NO3-N) | ||||||||||
| 0 | 39 | 6,784 | 1.00 (Reference) | 34 | 3,268 | 1.25 (0.68, 2.27) | 10 | 895 | 1.39 (0.59, 3.30) | |
| < 4 | 9 | 1,475 | 1.06 (0.51, 2.19) | 2 | 631 | 0.38 (0.09, 1.67) | 7 | 189 | 4.69 (1.79, 12.27) | |
| ≥ 4 | 11 | 1,395 | 1.39 (0.71, 2.71) | 13 | 745 | 1.99 (0.94, 4.22) | 5 | 195 | 3.48 (1.20, 10.06) | 0.01 |
| Total | 59 | 9,654 | 49 | 4,644 | 22 | 1,279 | ||||
| Abbreviations: ½-MCL, one-half the maximum contaminant level; CI, confidence interval; HR, hazard ratio. aAdjusted for age and pack-years of smoking. bDerived from a likelihood ratio test comparing fit of models with and without a cross-product term for smoking status and nitrate exposure. | ||||||||||