Abstract 149: Dietary intake of nitrate and nitrite, nitrate in drinking water, and ovarian cancer risk among postmenopausal women in Iowa.
Authors: Inoue-Choi Maki , Anderson Kristin E. , Cerhan James R. , Weyer Peter J. , Ward Mary H. 
Published: August 2014

Background: Nitrate and nitrite are precursors of N-nitroso compounds, known animal and human carcinogens. Nitrate and nitrite are common in foods, such as vegetables and processed meats, and nitrate is a contaminant of drinking water. We previously reported an increased ovarian cancer risk associated with higher nitrate intake in public water supplies in the Iowa Women's Health Study. Here, we report results based on an additional 12 years of follow-up and we present results for dietary nitrate and nitrite intake.

Methods: Among 28,555 postmenopausal women aged 55–69 y at baseline, we identified 315 incident epithelial ovarian cancers between 1986 and 2010. Dietary nitrate and nitrite intakes were assessed using a food frequency questionnaire at baseline. Information on drinking water source was obtained in 1989. Nitrate-nitrogen (NO3-N) levels in public water supplies (average level 1955-1988) and water sources (finished surface or ground water) were from a database of monitoring data for Iowa water utilities. Cox proportional hazards regression generated hazard ratios (HR) and 95% confidence intervals (CI). Because disinfection by-products (DBP) are higher in surface water and have been associated with increased risk for certain cancers, we determined whether the association between nitrate intake from drinking water and ovarian cancer risk differed by water source.

Results: Neither total dietary nitrate nor nitrite intake was associated with ovarian cancer risk after adjusting for age, energy intake, family history of ovarian cancer, number of live births, and history of unilateral oophorectomy. Nitrate and nitrite intakes from animal or plant sources, or processed meats were not associated with ovarian cancer risk. Among women who drank public water, we observed an increased risk for ovarian cancer with higher average levels of NO3-N (ptrend=0.004). Compared with women in the lowest quartile of NO3-N levels (&lt;0.36 mg/L), risk was 1.81 (95% CI=1.08-3.05) and 2.02 (95% CI=1.21-3.36) times higher in the third (1.0-2.5 mg/L) and fourth (&gt;2.5 mg/L) quartiles, respectively. Ovarian cancer risk among private well water drinkers was elevated (HR=1.52, 95% CI=0.91-2.53) but not statistically significantly different from the referent group. When stratified by water source, the positive association between NO3-N levels in public water and ovarian cancer risk was confined to women who drank water from surface sources (ptrend=0.007; pinteraction=0.04).

Conclusions: Dietary nitrate or nitrite intake was not associated with ovarian cancer risk. Our findings for nitrate intake from public water supplies suggest that nitrate intake from drinking water may increase ovarian cancer risk, particularly in the likely presence of other contaminants found in surface water. Further evaluation of DBP and other water contaminant levels on ovarian cancer risk in this population is warranted.

Citation Format: Maki Inoue-Choi, Kristin E. Anderson, James R. Cerhan, Peter J. Weyer, Mary H. Ward. Dietary intake of nitrate and nitrite, nitrate in drinking water, and ovarian cancer risk among postmenopausal women in Iowa. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 149. doi:10.1158/1538-7445.AM2013-149