Nitrate is a drinking water contaminant arising from agricultural sources and a precursor in the endogenous formation of N-nitroso compounds ( NOC ), which are possible bladder carcinogens.
A study has investigated the ingestion of nitrate and nitrite from drinking water and diet and bladder cancer risk in women.
Incident bladder cancers among a cohort of 34,708 postmenopausal women in Iowa ( 1986-2010 ) were identified.
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 ) more than 10 years ( N=15,577 ), researchers estimated average nitrate ( NO3-N ) and total trihalomethanes ( TTHM ) levels and the number of years exceeding one-half the maximum contaminant level ( NO3-N: 5mg/L, TTHM: 40 microg/mL ) from historical monitoring data.
Researchers identified 258 bladder cancer cases, including 130 among women more than 10 years at their PWS.
In multivariable-adjusted models, researchers observed non-significant associations among women in the highest versus lowest quartile of average drinking water nitrate concentration ( hazard ratio, HR=1.48; CI=0.92,2.40; p trend=0.11 ), and significant associations among those exposed greater than or equal to 4 years to drinking water with more than 5mg/L NO3-N ( HR=1.62; CI=1.06,2.47; p trend=0.03 ) compared to women with no years of comparable exposure.
TTHM adjustment had little influence on associations, and researchers 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 and HR=3.48; 95% CI=1.20,10.06 for average water NO3-N and greater than or equal to 4 years more than 5mg/L, respectively ).
Dietary nitrate and nitrite intakes were not associated with bladder cancer.
In conclusion, long-term ingestion of elevated nitrate in drinking water was associated with an increased risk of bladder cancer among postmenopausal women. ( Xagena )
Jones RR et al, Environ Health Perspect 2016; Epub ahead of print