SUNDAY September 23, 2007 (Foodconsumer.org) -- Use of drinking water with high levels of nitrates may increase risk of rectal cancer death, according to a new study by researchers from Kaohsiung Medical University in Kaohsiung, Taiwan, adding to evidence suggesting that exposure to nitrate in drinking water may raise cancer risk.

Nitrates do not pose any cancer risk. But these compounds can be endogenously converted to nitrite and subsequently to n-nitroso compounds, which are highly carcinogenic.

Early studies on the effect of nitrates in drinking water and cancer risk are inconsistent.   The researchers meant to add more evidence to prove or disprove the link between contamination of nitrates in drinking water and risk of death from rectal cancer.

For the study, Kuo H. W. and colleagues analyzed data on deaths of Taiwan residents from rectal cancer between 1999 and 2003 and nitrate-nitrogen levels in drinking water throughout Taiwan to determine if there is any association between nitrate levels and risk of rectal cancer deaths.

The researchers found those who were exposed to highest levels of nitrates in drinking water were significantly more likely to die from rectal cancer than those who were exposed to lowest amounts of the pollutants.

The results were published in the October 2007 issue of Journal of Toxicology and Environmental Health, Part A.

An early study by researchers from Center for Health Effects of Environmental Contamination, University of Iowa found that nitrate in drinking water was positively associate with risk of some cancers, but inversely with the risk for other cancers including rectal cancer.

In their study, Weyer PJ and colleagues analyzed cancer incidence in a cohort of 21,977 Iowa women aged 55-69 with 16,541 using a municipal supply and the rest using private wells.   The participants used the same water source for at least 10 years with 87 percent more than 20 years.

According to the study report, those who were among the quartile using drinking water with highest amounts of nitrate were less likely to develop rectal cancer, a finding that is contradictory to the current study.   The inverse association was also found between the nitrate level and uterine cancer.

However, the early study found those who had the highest intake of nitrate through their drinking water were 183 percent more likely to have bladder cancer and 84 percent more likely to develop ovarian cancer.

The results were published in the December 2001 issue of Epidemiology.