Health Stream Literature Summary - Issue 54 - June 2009

Nitrate in drinking water and risk of death from pancreatic cancer in Taiwan.
Yang, C.Y., Tsai, S.S. and Chiu, H.F. (2009) Journal of Toxicology and Environmental Health. Part A, 72(6); 397-401.

In drinking water, nitrates originate from numerous natural and man-made sources which include wastewater and agricultural and urban runoff. The maximum contaminant level (MCL) in drinking water for nitrate established by the U.S. Environmental Protection Agency (EPA) is 10 mg/L as nitrate-N, a level set to protect infants from methemoglobinemia. There have not been adequate studies however of the effectiveness of this regulatory limit for preventing other adverse health risks such as cancer. Nitrate can act as a procarcinogen by interacting with amines and amides in the stomach and gut to form a variety of N-nitroso compounds (NOC) (nitrosation). NOC are potent animal carcinogens and induce tumours at multiple organ sites including the pancreas. There have been few epidemiological studies conducted to address the association between nitrate in drinking water and cancer risk. Most of the epidemiological studies in humans have focused on gastric cancer and the results are controversial. This present study was undertaken in Taiwan to further explore whether nitrate levels in drinking water correlate with an increased rate of mortality from pancreatic cancer.

There were 322 municipalities in Taiwan included in this study. Data on all deaths of Taiwan residents from 2000 through 2006 were obtained from the Bureau of Vital Statistics of the Taiwan Provincial Department of Health. There was detailed information for each death on demographics including gender, year of birth, year of death, cause of death, place of death and residential district. Cases consisted of all eligible pancreatic cancer deaths occurring in individuals between 50 and 69 years of age. Controls were all other deaths excluding deaths from cancers previously reported to be associated with nitrate or NOC exposures. Control subjects were pair matched to cases by gender, year of birth and year of death. The levels of nitrate-nitrogen (N03-N) in each municipality were obtained from the Taiwan Water Supply Corporation, to which each waterworks is required to submit drinking water quality data. From each waterworks four finished water samples, one for each season, was collected. Of the 322 municipalities, 70 were excluded as they had more than one supply of drinking water and the exact population served by each could not be determined. The annual mean levels of N03-N for the year 1990 were collected. The municipalities of residence for all cancer cases and controls was identified from their death certificates and assumed to be the source of the subjects' nitrate exposure via drinking water.

There was 2412 pancreatic cancer cases with complete records collected from 2000-2006. The mean nitrate concentration in the drinking water of pancreatic cancer cases was 0.44 mg/L and for controls 0.42 mg/L. The odds ratios (OR) for death due to pancreatic cancer were higher for the two groups with high levels of nitrate in their drinking water but did not reach statistical significance. Adjustment for possible confounders only slightly altered the OR. The adjusted OR was 1.03 (0.9-1.18) for the group with water nitrate levels between 0.19 and 0.45 mg/L and 1.1 (0.96-1.27) for the group with nitrate levels of 0.48 mg/L or more.

These results show no statistically significant association between nitrate levels in drinking water and the risk of death from pancreatic cancer. These finding are consistent with recent studies in the United States. Future studies need to increase the precision of the estimation of the individual's intake of nitrate through both food and water and need to control for confounding factors including personal risk factors such as smoking.

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