■ The fluoridation of drinking water in New Zealand is not compulsory. However, we in the district of Whakatāne began fluoridating drinking water in 1969 when I was about eight. Shortly thereafter, fluoride-containing toothpaste became widely available in New Zealand, writes Dr Victor Luca.

All natural water sources in our district contain negligible levels of natural fluoride.

So, the introduction of fluoride in drinking water and toothpaste introduced two new sources of fluoride almost simultaneously that were not there when I was born.

I can still vividly recall those years prior to fluoridation. Those terrifying short walks from Saint Joseph’s Primary School, south down King Street and then a short left turn down Alexander Avenue. Then up a concrete path to the dental surgery located on the Allandale School campus to what was then called “the murder house”.

For a few years, I, like everyone else I knew, took a bit of a hammering at the hands of the dental nurses. It was a terrifying experience. In those days the drill was slow and anesthetic wasn’t used.

Once fluoride was added to drinking water and toothpaste most of my troubles seemed to magically evaporate.

A few decades later, a district-wide non-binding referendum was held in conjunction with the 2013 local body election in response to submissions during the annual plan process.

About 60 percent of residents who voted opted in favour of fluoridation.

We have voluntarily been adding fluoride to Whakatāne’s drinking water ever since.

The Health (Fluoridation of Drinking Water) Amendment Act 2021 amended the 1956 Health Act 1956, which enabled the Director-General of Health to direct councils to fluoridate drinking water supplies to establish nationally consistent decision-making on this health-related matter.

Kawerau District Council was directed to fluoridate in July of 2022 as was Tauranga City Council and Rotorua Lakes Council.

Ōpōtiki District Council is currently under active consideration for a directive to fluoridate. Whakatāne didn’t need to be directed since we voluntarily fluoridate.

The NZ Ministry of Health recommends that New Zealand drinking water contains between 0.7 and 1.0 mg/L of fluoride.

I am a chemist and when I was at university we had a lecturer who conducted research into the crystal structure of tooth enamel, which is essentially made of the mineral appetite (Calcium Phosphate) that has the chemical formula Ca5(PO4)3(F,Cl,OH). Appetite is a common mineral in many rocks.

The (F,Cl,OH) bit in the formula means that F- or Cl- or OH- can replace each other in the crystal structure. Fluoride makes the tooth enamel tougher. Fact!

Fluoride is proven to be beneficial for the strengthening of tooth enamel.

The evidence is quite compelling. The fluoride can be introduced (topically) by adding fluoride to toothpaste or through ingestion.

When you eat, food-derived acids are produced that dissolve a little of the enamel.

When you are not eating, the elements in saliva help replenish that enamel.

So, the enamel is in a constant state of dissolving and recrystallising.

Some folk are opposed to the addition of fluoride to drinking water supplies but don’t seem to be opposed to fluoride in toothpaste. Clearly these are two quite different ways of introducing fluoride.

Any chemical in large amounts can be toxic. As the famous Swiss-German Physician, Paracelsus (1493-1541), rightly stated, ‘dose makes the poison’. Paracelsus is considered to be the founder of modern toxicology.

The question is what dose is required to make a substance harmful. In very low concentrations the science has suggested that fluoride is relatively harmless.

There have been several large reviews of the thousands of scientific studies into the effects of fluoride on tooth decay and health.

For instance, the 2006 review by the US National Research Council (US National Academy of Sciences).

The Australian National Health & Medical Research Council published a major report in 2017 summarising the situation up to that date [1]. The following conclusions were made:

“The evidence shows that water fluoridation at current Australian levels reduces the occurrence and severity of tooth decay.

“Water fluoridation at current Australian levels is associated with dental fluorosis. In Australia, however, most dental fluorosis is very mild or mild, does not affect the function of teeth and is not of aesthetic concern to those who have it.

“There is evidence that water fluoridation at current Australian levels is not associated with cognitive dysfunction, lowered IQ, cancer, hip fracture and Down syndrome. There is no reliable evidence of an association between water fluoridation at current Australian levels and other human health outcomes.”

A later review of the science on this subject is the UK Chochrane Review of 2024 [2].

Science often proceeds in small steps rather than large leaps.

Small steps in the sense that evidence is built up slowly. Theories hold up as long as evidence doesn’t prove them wrong. Nor are all scientific studies made equal.

Some studies are flawed, others have weaknesses, and others lack robustness. We know with a high degree of certainty that fluoride in water is beneficial for reducing tooth decay, and until recently we had been reasonably sure that low doses of fluoride (< 1.5 mg/L) do not increase the risk of cancer and other diseases.

Then in the mid-to-late 2000s studies began to appear in the scientific literature that suggested that elevated levels of fluoride in drinking water might be of concern.

These studies suggested that more research was warranted, especially of the relationship between fluoride concentration and Neurodevelopmental Disorder (ND) effects in children. Children are not just young adults in the sense that their immune and other systems are developing rapidly.

A 2012 study published in the journal Environmental Health Perspectives [3] provided evidence of a link between high fluoride levels found naturally in drinking water in China and elsewhere in the world and lower IQs in children.

The paper looked at the results of 27 different studies, 26 of which found a link between high-fluoride drinking water and lower IQ.

The average IQ difference between high and low fluoride areas was 7 points, the study found. Other recent studies have supported a similar lowering IQ [4].

A comprehensive 2024 review of the current science by the National Institutes of Health, National Toxicology Programme concluded with moderate confidence, that higher levels of fluoride exposure, such as drinking water containing more than 1.5 mg/L fluoride, are associated with lower IQ in children [5]. Note the use of the words “with moderate confidence”.

A very recent 2025, seemingly robust study [6], has similarly suggested that low levels of fluoride in the urine of children are associated with a very slight lowering of IQ when fluoride is incorporated at a level of less than 1.5 mg/L.

There are also many recent seemingly robust studies that suggest that there are no neurodevelopmental effects in children from low fluoride doses [7]. What does seem certain is that if there is an effect then it is relatively weak.

A recently published study by Geier and Geier [8] concluded that there were dose-dependent and overall significant associations between increasing fluoride exposure and reduced tooth decay. They also found associations between increasing fluoride exposure and increasing rates of NDs. Given that both beneficial and harmful effects were found, the authors recommended that new risk-benefit analyses be undertaken regarding water fluoridation programmes. These future studies should be undertaken on databases of large populations. In other words, we should keep studying.

Most recently, a study by a US research group concluded that “children exposed to recommended levels of fluoride in drinking water exhibit modestly better cognition in secondary school, an advantage that is smaller and no longer statistically significant at age ~60”.

The study was published in the highly reputable journal Science Advances [9].

So, where does all this leave us in regards to the fluoridation of drinking water?

Do we trade off improved dental health with suspected but unproven very minor ND effects in children?

My answer is that we go with the best scientific advice available.

But what do we do when we have a hung jury? Should we err on the side of caution?

I would say we continue with the current practice, which shows clear benefits in reducing tooth decay until such time as conclusive evidence indicates the practice be discontinued. This seems to be what the Ministry of Health concluded a while ago.

For those concerned about being deprived their right to choose, or not being prepared to make potential trade-offs, my advice would be to install a point-of-use filter system that is capable of removing fluoride. They are not overly expensive.

In the meantime, our health authorities do not give local authorities a choice. They must do what they are told as has been the recent case with rates capping.

When there are so many significant health threats that remain unaddressed, such as obesity and air pollution, and many other existential threats, such as nuclear war and climate change, why worry about something that has clear benefits for your teeth and at worst a potentially minuscule effect on neurological development.

A complete version of this column with references can be viewed on my website or on my Substack.