Researcher to look at link between nitrates in drinking water and bowel cancer rates

The researcher behind a ground-breaking study showing potentially harmful levels of nitrates in drinking water is planning further work that will establish if there is a link with rates of bowel cancer.

Tap water Source:

By Conan Young of

It will make use of a Statistics New Zealand database that keeps a record of every time a person interacts with a government agency.

In February, the preliminary study found between 300,000 and 800,000 New Zealanders were exposed to potentially harmful levels of nitrate in their drinking water.

However it left two important questions unanswered.

Did people with bowel cancer have unsafe levels of nitrate in their drinking water?

And even if they did, could it have been something else that caused the cancer in the first place?

Lead author Dr Tim Chambers said the next phase of his research involved overlaying the nitrate levels found in the first phase with rates of bowel cancer in order to show if one followed the other.

"There's a very good data keeping structure in New Zealand on things like cancer rates and also other things of interest, other confounders that we would want to include in studies, like people's age, sex, and income."

The reason this information existed was because of a database kept by Statistics New Zealand that pulled together all of the occasions each and every one of us had an interaction with a government agency.

Your tax records, applications for a benefit, when you register to vote, hospital admissions - it is all available to researchers in a single place.

The data was collated in blocks of 2000 neighbouring households, rather than per home or per individual, so as to preserve people's privacy.

Chambers said nobody was keeping tabs on how likely it was people in these neighbourhoods were engaging in lifestyle factors that also contributed to bowel cancer, including lack of exercise, smoking, alcohol and processed meat.

But research showed the poorer you were, the more likely it was you were engaging in some or all of them.

This made the database a goldmine for anybody wanting to weigh the contribution of these lifestyle factors to bowel cancer versus that made by nitrates in people's drinking water.

He made the point that while these other factors could all be avoided, what came out of your tap could not.

"The fact that people could potentially be getting sick from their water is kind of inexcusable. Whereas if people decide they want to have saveloys for breakfast or drink a 40 ounce for lunch, that's completely their own personal choice right, and as government we should be doing things to reduce alcohol consumption and smoking, and they are.

"But those are lifestyle decisions, water consumption shouldn't be."

The next phase of the research had attracted attention from the lead author of a 2018 Danish study that found a clear relationship between the amount of nitrate in people's drinking water and rates of bowel cancer.

Jorg Schullehner had agreed to come on board as a supervisor and said it was important the same work they did was replicated around the world.

While these studies would never be able to show nitrates in drinking water were causing bowel cancer, it was all part of building up a body of evidence that showed there was an association, he said.

"Looking at studies in other countries with different designs, with different strengths and different limitations that complement each other rather well, and if they also find these correlations then it's another piece of evidence. And then at some point there might be enough evidence for us to say we are kind of convinced."

Back in New Zealand, Chambers was now preparing a funding application to the Health Research Council to allow the next part of his research to proceed.

He faced a long wait however, with final decisions on funding not made until the start of next year.