Waikato Times

Nitrates unlikely to increase cancer risk

- Peter Cressey, Belinda Cridge, Catherine McLeod, Glenda Lewis

A2018 Danish research study reported an associatio­n between the level of nitrates in drinking water and the occurrence of bowel cancer. A subsequent New Zealand study also concluded it was a risk factor.

These studies raised antennae because we have a high incidence of bowel cancer, and are already on red alert about our freshwater.

Some private drinking water sources, such as shallow wells, have elevated nitrate levels. But for the vast majority of New Zealanders this is not an issue as the average nitrate content in reticulate­d, and therefore regulated, water supplies is generally less than 2mg per litre.

While associatio­ns such as that reported in the Danish study can be concerning, they do not necessaril­y prove ‘‘cause and effect’’. When investigat­ing the possible effects of chemicals over lifetimes of eating or drinking, it is difficult to pin down causes. While some statistica­l correlatio­ns highlight potential issues, others may have no biological connection.

Nitrates are important in the human body for making nitrites, which combat bacteria in the mouth and stomach, and nitric oxide that makes our arterial walls flexible, which guards against heart disease and stroke.

The Danish study and others looked at drinking water nitrates alone or considered food and drinking water nitrates as separate. Drinking water accounts for about 10 per cent of the nitrates people consume, with most coming from green vegetables.

So how did these researcher­s propose that nitrates could cause cancer, and is it plausible?

The suspicion is that nitrosamin­es, formed from nitrites and other compounds called amines, might somehow be responsibl­e. The formation of nitrosamin­es is understood to be cancelled out by antioxidan­ts in food, such as vitamin C, so it is important to look at food and water together.

Green vegetables, the main source of nitrates in the diet, are also rich in antioxidan­ts which would stop nitrosamin­es forming from nitrates in food and water.

The NZ Food Safety Science & Research Centre commission­ed ESR to assess the levels of nitrates Kiwis are consuming from water and food. MBIE and Fonterra funded the research.

Peter Cressey, a chemical risk assessor at ESR, and coresearch­er, toxicologi­st Dr Belinda Cridge, used informatio­n from national nutrition surveys that quizzed about 8000 New Zealanders on their eating and drinking habits. They wanted to know how much water was consumed together with food, or within a short time of eating.

They estimated the amount of nitrates the cohort ingested in a day, and the extent to which the antioxidan­ts in their food would likely cancel out any excess nitrates.

On average, the nitrates New

Zealanders take in from food and water add up to about onequarter of the internatio­nally agreed acceptable daily limit, with less than 10 per cent coming from drinking-water.

According to ESR’s calculatio­ns, only 2.6 per cent of nitrate consumptio­n for adults, and 0.7 per cent for children, is from drinking-water consumed on its own and not in close (less than 1 hour) proximity to eating.

This demonstrat­es that considerin­g nitrates from drinking water and food as separate does not reflect actual human behaviour.

The researcher­s concluded, based on current evidence, that ‘‘it is highly unlikely that nitrates in drinking water or the diet present an increased risk of cancer’’.

It is vital that New Zealanders keep up – and in many cases, significan­tly increase – their consumptio­n of fruit and vegetables as a protection against bowel and other cancers.

Read the full report, and a Q&A, at nzfssrc.org.nz/news

Peter Cressey and Dr Belinda Cridge work at ESR; Dr Catherine McLeod is the director of the FSSRC; and Glenda Lewis is a science writer.

 ??  ?? New Zealanders should significan­tly increase their consumptio­n of fruit and vegetables to protect against bowel and other cancers.
New Zealanders should significan­tly increase their consumptio­n of fruit and vegetables to protect against bowel and other cancers.

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