Nitrate in public water supplies and risk of bladder cancer.
BACKGROUND
Nitrate is a precursor compound in the formation of N-nitroso compounds, most of which are potent animal carcinogens. N-nitroso compounds and their precursors have not been extensively evaluated as bladder cancer risk factors.


METHODS
We conducted a population-based case-control study of bladder cancer in Iowa. Cases were men and women newly diagnosed with bladder cancer in 1986-1989. Nitrate data for Iowa public water supplies were sparse before the 1960s. To reduce misclassification by unknown nitrate levels, we included only those who used public supplies with nitrate data for 70% or more of their person-years since 1960 (808 cases, 1259 controls).


RESULTS
Among controls, the median average nitrate level for their Iowa residences with public water supplies was 1.3 mg/liter nitrate-nitrogen (interquartile range = 0.6-3.0). After adjustment for confounders, we found no increased risk of bladder cancer with increasing average nitrate levels in drinking water; the highest quartile odds ratio for women was 0.8 (95% confidence interval = 0.4-0.8), and for men 0.5 (0.4-0.8). We observed no association among those with high water nitrate exposure (>median) and low (<median) vitamin C intake compared with those who had low water nitrate and high vitamin C intake.


CONCLUSIONS
Our data suggest that long-term exposure to nitrate in drinking water at levels in this study (90th percentile 5.5 mg/liter nitrate-nitrogen) is not associated with risk of bladder cancer.
Ward
Mary H
MH
Occupational Epidemiology Branch, Division of Cancer Epidemiology and Genetics, National Cancer Institute, National Institutes of Health, Department of Health and Human Services, Bethesda, MD 20892-7240, USA. wardm@mail.nih.gov
Cantor
Kenneth P
KP
Riley
David
D
Merkle
Shannon
S
Lynch
Charles F
CF
D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D016022:Case-Control Studies; D015986:Confounding Factors, Epidemiologic; D004781:Environmental Exposure / Q000009:adverse effects; D005260:Female; D006801:Humans; D007407:Interviews as Topic; D007484:Iowa / Q000453:epidemiology; D016015:Logistic Models; D008297:Male; D008875:Middle Aged; D009566:Nitrates / Q000009:adverse effects / Q000032:analysis*; D012307:Risk Factors; D011795:Surveys and Questionnaires; D001749:Urinary Bladder Neoplasms / Q000139:chemically induced / Q000453:epidemiology*; D014874:Water Pollutants, Chemical / Q000009:adverse effects / Q000032:analysis*; D014881:Water Supply
D009566:Nitrates; D014874:Water Pollutants, Chemical