Nitrate from drinking water and diet and bladder cancer among postmenopausal women in Iowa

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From: Environmental Health Perspectives(Vol. 124, Issue 11)
Publisher: National Institute of Environmental Health Sciences
Document Type: Report
Length: 8,093 words
Lexile Measure: 1490L

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Abstract :

BACKGROUND: Nitrate is a drinking water contaminant arising from agricultural sources, and it is a precursor in the endogenous formation of N-nitroso compounds (NOC), which are possible bladder carcinogens. OBJECTIVES: We investigated the ingestion of nitrate and nitrite from drinking water and diet and bladder cancer risk in women. METHODS: We identified incident bladder cancers among a cohort of 34,708 postmenopausal women in Iowa (1986-2010). Dietary nitrate and nitrite intakes were estimated from a baseline food frequency questionnaire. Drinking water source and duration were assessed in a 1989 follow-up. For women using public water supplies (PWS) 10 years (n = 15,577), we estimated average nitrate (N[O.sub.3]-N) and total trihalomethane (TTHM) levels and the number of years exceeding one-half the maximum contaminant level (N[O.sub.3]-N: 5 mg/L, TTHM: 40 pg/mL) from historical monitoring data. We computed hazard ratios (HRs) and 95% confidence intervals (CIs), and assessed nitrate interactions with TTHM and with modifiers of NOC formation (smoking, vitamin C). RESULTS: We identified 258 bladder cancer cases, including 130 among women 10 years at their PWS. In multivariable-adjusted models, we observed nonsignificant associations among women in the highest versus lowest quartile of average drinking water nitrate concentration (HR = 1.48; 95% CI: 0.92, 2.40; [p.sub.trend] = 0.11), and we found significant associations among those exposed [greater than or equal to] 4 years to drinking water with 5 mg/L N[O.sub.3]-N (HR = 1.62; 95% CI: 1.06, 2.47; [P.sub.trend] = 0.03) compared with women having 0 years of comparable exposure. TTHM adjustment had little influence on associations, and we observed no modification by vitamin C intake. Relative to a common reference group of never smokers with the lowest nitrate exposures, associations were strongest for current smokers with the highest nitrate exposures (HR = 3.67; 95% CI: 1.43, 9.38 for average water N[O.sub.3]-N and HR = 3.48; 95% CI: 1.20, 10.06 and [greater than or equal to] 4 years 5 mg/L, respectively). Dietary nitrate and nitrite intakes were not associated with bladder cancer. CONCLUSIONS: Long-term ingestion of elevated nitrate in drinking water was associated with an increased risk of bladder cancer among postmenopausal women.

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Gale Document Number: GALE|A484313023