A medical expert is concerned both of Christchurch’s main mayoral candidates oppose water fluoridation.

“The message is clear, the science is clear. The benefits are enormous,” Canterbury medical officer of health Alistair Humphrey said.

Both Lianne Dalziel and John Minto said they were against fluoridation of Christchurch’s water supply during The Press’ mayoral debate on Tuesday.

Minto said he believed there was evidence that fluoride caused more harm than good. Dalziel said it would cost too much.

“It’s a debilitating disease that is easily fixed,” Humphrey said.

He said alternatives such as fluoridated toothpaste did not have the same benefits.

“It’s fluoride in the water that prevents dental caries the best, and it’s our poorest part of our community who suffer the most.

“I think that those candidates talking [on Tuesday] night could claim to represent the more vulnerable end of the spectrum.”

He said there were benefits that reached beyond the people directly affected by dental diseases.

“One of the things people don’t realise is how much dental caries, for example, ties up operating theatres.”

Christchurch has a shortage of operating theatres, particularly since the 2010 and 2011 earthquakes.

A shortage of theatres means longer surgery waiting lists and increased costs for the Canterbury District Health Board.

“They tie up huge amounts of surgical resource that could otherwise be used to be treating other people who do not have preventable problems,” Humphrey said.

Dalziel said the Christchurch City Council opposed the Local Government New Zealand resolution to fluoridate town water supplies in 2015 because of the expense.

“I’m not opposed to fluoride – I had fluoride tablets as a kid. I just know that because of the nature of our water supply, the multiple points that require fluoridation makes it way more expensive than other areas.”

Minto said he had a change of heart on fluoridation.

“Absolutely five years ago I would have agreed wholeheartedly with [Humphrey] . . . but there’s a lot that’s happened for me since then.”

He said he had read a lot on the issue, and believed there was “a seriously arguable case” the fluoride might do more harm than good.

“It’s raised a whole lot of questions that I wasn’t aware of about the side effects of fluoride.

“I’ve got a science background. I’m not a conspiracy theorist.”