A new study from the University of Iowa in Iowa City suggests the limit set for a cancer-causing compound found in U.S. tap water may be too high, putting women at increased risk for bladder cancer.
According to the report, women who drank tap water that contained levels of nitrates below the maximum level of 10 milligrams (mg) per litre set by the US Environmental Protection Agency (EPA) were still nearly three times more likely to develop bladder cancer compared with women who consumed much lower levels of the contaminate. The study included nearly 22,000 Iowa women aged 55-69 years who had used the same water supply for more than 10 years--with most drinking the water for more than 20 years.
Nitrate is a pollutant that can leech into municipal water supplies from commercial fertilizers, as well as human and animal waste. In the stomach, about 20% of nitrates can be transformed into nitrites, which can be converted into cancer causing compounds.
The researchers found that the risk of bladder cancer rose in tandem with nitrate levels in the communities' water supplies regardless of smoking, intake of vitamins C and E, and nitrates in the diet. Smoking can increase nitrate exposure, as can certain vegetables, while the vitamins C and E can counteract the carcinogenic effects of nitrates.
According to the researchers, these findings warrant further study. The researchers did not collect data on the volume of tap water consumed by the women, or how much water they consumed outside their home. The study does not confirm that nitrates were responsible for the increased bladder cancer risk.
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