Ingestion of Nitrate and Nitrite from Drinking Water and Diet: a Prospective Analysis of Epithelial Ovarian Cancer Risk among Postmenopausal Women in IowaAbstract Number:1930 Maki Inoue-Choi*, Rena Jones, Kristin Anderson, Kenneth Cantor, James Cerhan, Stuart Krasner, Kim Robien, Peter Weyer, and Mary Ward Maki Inoue-Choi* National Cancer Institute, United States, E-mail Address: [email protected] Search for more papers by this author , Rena Jones National Cancer Institute, United States, E-mail Address: [email protected] Search for more papers by this author , Kristin Anderson University of Minnesota, United States, E-mail Address: [email protected] Search for more papers by this author , Kenneth Cantor National Cancer Institute, United States, E-mail Address: [email protected] Search for more papers by this author , James Cerhan Mayo Clinic, United States, E-mail Address: [email protected] Search for more papers by this author , Stuart Krasner Metropolitan Water District og Sourthern California, United States, E-mail Address: [email protected] Search for more papers by this author , Kim Robien George Washington University, United States, E-mail Address: [email protected] Search for more papers by this author , Peter Weyer University of Iowa, United States, E-mail Address: [email protected] Search for more papers by this author , and Mary Ward National Cancer Institute, United States, E-mail Address: [email protected] Search for more papers by this author AbstractBackground: Nitrate and nitrite are precursors in the endogenous formation of N-nitroso compounds (NOC), potential human carcinogens. Nitrogen from agricultural fertilizers and other sources can contaminate drinking water supplies. Objective: To evaluate the association of nitrate/nitrite ingestion and ovarian cancer risk.Methods: Dietary nitrate and nitrite intakes were assessed using a food frequency questionnaire among 28,555 cancer-free postmenopausal women enrolled in the Iowa Women’s Health Study in 1986. Historical data on drinking water source was obtained from the 1989 survey. Nitrate-nitrogen (NO3-N) and disinfection byproduct (DBP) levels were estimated for Iowa public water utilities; average levels were computed for the women’s duration of use of each public supply. Multivariable-adjusted hazard ratios (HR) and 95% confidence intervals (CI) were calculated using Cox proportional hazards regression. We tested interactions of nitrate with DBPs and selected dietary intakes known to influence NOC formation.Results: Through 2010, 315 incident invasive ovarian cancers were identified. Ovarian cancer risk was 2.2 times higher (95%CI=1.3-3.6) among women in the highest quartile (=2.98 mg/L) compared to the lowest quartile of NO3-N (=0.47 mg/L) in public water, regardless of DBP levels (ptrend=0.001). Risk among private well users was elevated (HR=1.5, CI=0.9-2.5). Associations were stronger when vitamin C intake was <median, especially for private well use (pinteraction=0.01). Dietary nitrate intake was associated with lower ovarian cancer risk (HRQ5 vs. Q1=0.6, CI=0.4-0.9, ptrend=0.01). Ovarian cancer risk increased by 11% with each 0.1 mg/d increment in nitrite intake from processed meats (CI=1.0-1.2).Conclusions: Higher nitrate exposures from public water supplies and private well use were associated with increased ovarian cancer risk, especially with low vitamin C intake. Higher nitrite intake from processed meats may increase ovarian cancer risk.