Tuesday April 24 1:57 PM ET
Nitrates May Up Bladder Cancer Risk in Women

NEW YORK (Reuters Health) - The limit set for a cancer-causing compound found in tap water may be too high, putting women at increased risk for bladder cancer, results of a study suggest.

According to the report, women who drank tap water that contained levels of nitrates below the maximum level of 10 milligrams (mg) per liter 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 compared women who drank water with more than 2.46 mg of nitrate per liter for more than 10 years with those who consumed less than 0.36 mg of nitrate per liter of water.

The study in the May issue of Epidemiology also found a slightly higher risk of ovarian cancer associated with nitrate-contaminated water and lower risks of uterine and rectal cancers.

``Our study suggests that nitrate levels much less than (the EPA's maximum limit) could be a serious health concern,'' Dr. Peter J. Weyer of the University of Iowa in Iowa City, said in a prepared statement.

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 ``some of the strongest known'' cancer causing compounds, the authors write.

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. About 75% used a municipal supply and the remainder used a private well when the study began in 1986.

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.

While the association between nitrate contamination in drinking water and bladder cancer supports previous research, the findings warrant further study, Dr. James R. Cerhan, a co-author from the Mayo Clinic in Rochester, Minnesota, said in a prepared statement. The researchers did not collect data on the volume of tapwater consumed by the women, or how much water they consumed outside their home. The study can not confirm that nitrates were responsible for the increased bladder cancer risk.

In other findings, there was no association between nitrate levels in water and other types of cancer including leukemia, melanoma, colon, kidney, breast and lung cancers.

SOURCE: Epidemiology 2001;11:327-338.