Cancer risk from nitrates deemed unlikely – Expert Reaction

New research concludes it is “highly unlikely” that nitrates in drinking water or food increase bowel cancer risk, based on existing evidence.

Carried out by ESR scientists, the research was jointly funded by MBIE and Fonterra. According to the study, drinking water accounts for less than 10% of New Zealanders’ exposure to nitrates, and the nitrates that Kiwis take in from food and water each day are well within – about one-quarter – of the internationally-accepted amount. The authors will present the findings at a free webinar tomorrow.

The SMC asked experts to comment on the research. 

Dr Tim Chambers, Senior Research Fellow, Department of Public Health, University of Otago, comments:

“The ESR report, co-funded by Fonterra and MBIE, aimed to investigate the relative contributions of water and food to New Zealanders’ overall nitrate intake in light of emerging evidence from epidemiological and experimental studies suggesting nitrate could increase colorectal cancer risk.

“Importantly, the authors acknowledge the likely biological pathway for ingested nitrate increasing the risk of cancer, but did not specifically mention the conclusion of the International Agency for Research on Cancer (IARC) that ingested nitrate or nitrite under conditions that result in endogenous nitrosation is probably carcinogenic to humans (group 2A).

“This process is complicated and is influenced by dietary factors (especially the balance of red meat, fruit and vegetables) and gut microflora. The interplay of these factors determines the synthesis of N-nitroso compounds, a class of cancer-causing chemicals.

“The authors concluded “it is highly unlikely that nitrates in drinking water or the diet present an increased risk of cancer” largely based on the relatively minor [about 10%] contribution of drinking water to the average New Zealander’s overall nitrate intake.

“However, our earlier research in New Zealand has highlighted the average New Zealander is either at low or no risk from nitrate in drinking water based on international studies. A detailed analysis of the approximately 800,000 New Zealanders who are potentially at risk would have been more informative.

“The authors also assume that any nitrate from water consumed with a meal, or as another type of beverage [eg coffee], poses zero risk to human health, regardless of the potential imbalance between nitrate and antioxidants. To my knowledge, there is very limited research investigating the level of antioxidants required to nullify the effect of any given level of nitrate in drinking water on endogenous nitrosation.

“It is great to see additional attention dedicated to this important health issue. However, the research aims and analyses within this report were never designed to support the definitive conclusions used in public statements.”

Conflict of interest statement: “Dr Chambers’ role at the University of Otago is funded by a donation from the GAMA foundation”