Study finds nitrates increase bladder cancer risk. (EH Update)
Full Text: COPYRIGHT 2004 National Environmental Health Association
Nitrate in drinking water is associated with an increased risk of bladder cancer, according to a University of Iowa (UI) study that looked at cancer incidence among nearly 22,000 Iowa women.
The study results suggest that even low-level exposure to nitrates over many years could increase certain types of cancer, said Peter Weyer, associate director of the UI Center for Health Effects of Environmental Contamination (CHEEC) and one of the lead authors. The study was published in the May 2001 issue of the journal Epidemiology.
"The positive association we found between nitrate contamination in drinking water and bladder cancer is consistent with some previous data. However, this is something that warrants follow-up research," said Weyer, who co-authored the article with James R. Cerhan, M.D., Ph.D., an investigator with the department of health sciences research at the Mayo Clinic in Rochester, Minnesota.
The researchers assessed nitrate exposure from drinking water in 21,977 women who were participants in the Iowa Women's Health Study. The women were between 55 and 69 years of age in 1986 (at the start of the study). They resided in a total of 400 Iowa communities and had used the same drinking-water supply for more than 10 years. Approximately 16,500 of the women received their water from municipal water supplies; the remaining women used private wells.
No individual water consumption data were available, so the researchers assigned each woman an average level of exposure to nitrate. The assigned levels were based on data collected between 1955 to 1988 on nitrate levels in the community water supply each woman used. No nitrate data were available for women who used private wells.
The researchers used cancer incidence data from the Iowa Cancer Registry for 1986 to 1998 and adjusted for factors such as smoking and nitrate in the diet. They found a greater risk for bladder cancer as the nitrate levels in the community water supplies increased. Women whose average drinking-water nitrate exposure level was greater than 2.46 milligrams per liter (mg/L) (nitrate-nitrogen) were 2.83 times more likely to develop bladder cancer than women with the lowest level of nitrate exposure (less than 0.36 mg/L).
Nitrate is produced naturally within the body; environmental sources include food (including many vegetables), contaminated drinking water, cigarette smoking, and certain medications. Drinking water can account for a substantial proportion of the total nitrate intake. Up to 20 percent of ingested nitrate is transformed in the body to nitrite, which can then undergo transformation in the stomach, colon, and bladder to form N-nitroso compounds. These compounds are known to cause cancer in a variety of organs in more than 40 animal species, including higher primates.
Weyer emphasized that additional studies are needed to look at possible links between nitrate levels in drinking water and cancer, particularly with respect to refining exposure assessments.
"From a public health perspective, source water protection is a main concern. Sources of nitrate that can affect water supplies include fertilizers, human waste, and animal waste," he said. "All of us, rural and urban residents alike, need to be more aware of how what we do as individuals can affect our water sources and, potentially, our health."
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