Relationship of Nitrate Exposure in Water Supplies and Cancer Risk

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UnityPoint Health - John Stoddard Cancer Center

Relationship of Nitrate Exposure in Water Supplies and Cancer Risk

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Relationship of Nitrate Exposure in Water Supplies and Cancer Risk

There has been recent discussion in the media about the relationship of nitrate ingestion from drinking water and several cancers. 

Nitrate is found in many foods with the highest concentrations in leafy green vegetables and root vegetables. In the body nitrate is converted into N-nitroso compounds, most of which are carcinogens (cancer causing). Because the formation of N-nitroso compounds is inhibited by vitamin C, polyphenols and other protective compounds present in high levels in most vegetables, dietary nitrate intake does not appear to result in significant N-nitroso compound formation.

Nitrate Levels in Water

Nitrate levels in our water systems have increased largely due to applications of inorganic fertilizers and animal manure in agricultural areas. Since approximately half of all applied nitrogen drains from agricultural fields to contaminate surface water and groundwater, concentrations of nitrate in our water systems have also increased and this trend of increasing contamination of our water supply by nitrate is expected to continue. The maximum contaminate level for nitrate in public drinking water in the United States is set at 10 mg/L = 10PPM. The maximum contaminate level was set to protect against infant methemoglobinemia; however other health effects, including cancer were not considered.

Increased nitrate in water supplies has been linked to colon, ovarian, thyroid, kidney and bladder cancers with the strongest association with colon cancer resulting in an estimated 6,500 cases of nitrate-attributable cancers. In most studies the increased risk of cancers was associated with nitrate levels well below the maximum contaminate level of 10 PPM, in fact a study from Denmark reported a statistically significant increase in colon cancer with nitrate in drinking water at levels of 0.7-2 PPM. This was particularly true for men with high red meat intake. A study from Iowa observed an increased risk of colon cancer for drinking water nitrate levels above 5 PPM for individuals with above median red meat consumption and low vitamin C intake.

Based on current data the level of nitrate in Des Moines water from the Fleur plant is 8 PPM and that of West Des Moines water is 0.6 PPM. The state average based on a 2015 analysis from the Environmental Working Group (EWG) was 0.995 PPM with a national average of 1.01 PPM. The health guideline, defined as 1 in a million cancer risk, is 0.14 PPM. Despite the fact that Des Moines water complies with federal standards (nitrate levels less than 10 PPM) the amount of nitrate in the drinking water is 8 times that of the national average and would appear to pose a small increased risk of colon cancer in susceptible individuals when consumed over years.

The best way to protect yourself from drinking water nitrate associated risk of cancer is to drink filtered water. Bottled water may not be the answer since the bottled water industry is not required to disclose the results of any contaminant testing that is does. The best way to know if the water you are drinking is free from contaminants is to contact the bottler and ask for the latest testing results. Neither the EPA nor FDA certifies bottled water. The best way to learn more about your tap supply is to read your water supplier’s annual water quality report. Nitrate can be removed by reverse osmosis filters but not by carbon filters. Also to minimize the formation of N-nitroso compounds eat a diet high in fresh fruits and vegetables and minimize the consumption of red meats, particularly those that are charred on a grill.

Conclusion

An important point to remember is that there are many other lifestyle factors that can reduce your overall risk of cancer and that reducing drinking water nitrate exposure is only a small part of a cancer risk reduction strategy. In order to fully leverage lifestyle strategies for cancer risk reduction I advocate the following: maintain a normal body weight and eat a mainly plant based diet avoiding processed and fast foods, learn to manage stress through breathing exercises or meditation, get 7-9 hours of quality sleep every night, exercise daily for at least 30 minutes, get outside everyday and enjoy nature, be compassionate to yourself and love yourself, enjoy energetic and nurturing social relationships, cultivate a spiritual practice, limit alcohol consumption and if you use tobacco products, quit.

References: 

- Temkin A, et al. Exposure-Based Assessment and Economic Valuation of Adverse Birth Outcomes and Cancer Risk Due to Nitrate in United Sates Drinking Water. Environmental Research. 2019; June 11.

- Ward MH, et al. Drinking Water Nitrate and Human Health: An Updated Review. International Journal of Environmental Research and Public Health. 2018;15:1557-1588.

- DeRoos AJ, et al. Nitrate in Public Drinking Water Supplies and the Risk of Colon and Rectum Cancers. Epidemiology. 2003;14:640-649.

 - Zirkle KW, et al. Assessing the Relationship Between Groundwater Nitrate and Animal Feeding Operations in Iowa. Sci Total Environ. 2016 October 1:1062-1068.

- Inoue-Choi M, et al. Nitrate and Nitrite Ingestion and Risk of Ovarian Cancer Among Postmenopausal Women in Iowa. Int J Cancer. 2015; 137(1): 173-182.

- Jones RR, et al. Nitrate from Drinking Water and Diet and Bladder Cancer Among Postmenopausal Women in Iowa. Environ Health Perspect. 2016;124: 1751-1758.