In recent weeks we have seen a revival of the water fluoridation “debate”. Perhaps the question we need to ask is “what is the debate really about?”

The science of fluoride in water is effectively settled. It has been one of the most thoroughly worked questions in public health science over some decades. There is a voluminous scientific and lay literature that needs to be considered.

There is no doubt that the presence of low amounts of fluoride in water (either naturally occurring or adjusted to between 0.7 and 1 mg/litre) reduces the incidence of dental caries and this is even in advanced economies where dental hygiene has been much improved and where fluoride toothpastes are available. In some countries, fluoride need not be added to the water supply because their geology naturally provides water with fluoride in at least these concentrations. But for some decades, in countries such as New Zealand, where fluoride levels are very low in natural water, fluoride has been added to the water supply.

Notably, both the very young and the old benefit from fluoride in the water supply. They develop fewer dental caries and thus have a significant reduction in the downstream effects such as the need for invasive dental surgery associated with problematic dental status. As in all populations the burden of poor dental health is considerably greater for those in less advantaged socioeconomic conditions and it is this population that benefits most from water fluoridation.

In other areas of the world, natural levels of fluoride in water can reach well above 4 mg/litre – this level is considered by authorities to be the level at which water is still determined to be perfectly safe for human consumption. It is absolutely clear that at doses used in New Zealand to adjust the natural level to a level consistent with beneficial health effects (0.7-1.0mg/litre), there is no health risk from fluoride in the water. Like any agent, including salt, sugar and water itself, if you eat or drink enough it can become toxic. At the doses used in New Zealand water, however, one would in all likelihood become very ill or succumb to water intoxication before any toxic effect of fluoride was discernable.

However there is one side effect of fluoride that is found even at this low level of fluoride in the water supply; in a portion of the population, it causes minimal white mottling of the enamel of the permanent teeth. This is very rarely discernible and is definitely not the severe fluorosis that is so often pictured on websites of those opposed to fluoridation of the public water supply. The latter is associated with drinking water with very high naturally occurring levels of fluoride (more than ten times levels in New Zealand water after fluoridation) or from other sources of high fluoride – for example that found in some forms of black tea, generally in parts of Asia. The exposures needed are chronic exposures at levels many times that in our water supply.

So why is there any issue at all? There are at least two primary questions on which public debate seems to be hinged.

The first issue is an inherent challenge for any public health intervention: How to balance the common good of a population-based intervention with individual rights? This is primarily a question of societal values not science. Indeed, the balance between doing good (reducing caries) and not doing significant harm (minimal dental mottling) is scientifically clear. Thus in some ways any remaining debate has analogies to the immunization situation and to the imposition of regulations such as those requiring the wearing of seat belts. However whether to apply the science-based knowledge in this equation is a question of public health ethics and societal values.

The second issue is yet another values debate: Can food be used as a medium for delivering a public heath intervention? Is it OK for public water to be manipulated for an additional health benefit or for a potentially medicinal purpose? As it happens we already do so with iodine – our salt is iodised to prevent the developmental delay (cretinism) and goiters (big thyroid glands) associated with iodine deficiency and which was so common in New Zealand 100 years ago. There is no scientific issue here -it is purely an issue of values.

But because both such questions are values-based, for many people they are difficult to discuss. As with other issues where science and values are seen to converge – such as climate change – it is often easier for those seeking to advance values-based concerns to make the science sound scary or more uncertain than it really is. Indeed, it becomes a tactic amongst those who become passionate about their cause. Because biology and medicine are complex, studies can be difficult to put in perspective and odd results can be given undue weight. I have discussed this problem extensively elsewhere (http://www.pmcsa.org.nz/wp-content/uploads/Interpreting-Science-April-2013.pdf).

The fluoride debate is based in no small part on numerous examples of inappropriate extrapolation from what happens at hugely higher doses of fluoridation, combined with what is frankly scaremongering. Further, because the way one looks for side effects following population interventions requires particular epidemiological approaches, the language of evidence-based medicine can be confusing to the non-expert and easily exploited.

With regard to fluoride, there have been genuine concerns raised regarding risks of bone disease, thyroid disease, brain disease and cancer. While these issues have been settled, they continue to be emphasized by those who oppose fluoride. Some of this continued emphasis is based on inappropriate interpretations of studies in rats or from humans who have fluoride poisoning or live in areas where there are extremely high concentrations of fluoride naturally occurring in the water or diet. Obviously the medical and public health science community has put a lot of effort into being sure that this is not the case at the doses being used to adjust natural levels in water. Safety has been the subject of major assessments by many health authorities in Western countries. It is clear that there is no risk of such disorders at the doses of fluoride being used and extensive epidemiological surveys have repeatedly confirmed this to be the case.

So why does this concern continue? The misuse or inappropriate and alarmist use of science is a classic example of science being a proxy for values debates. Others, who have a more skeptical view of the medical-scientific sector, have seen this as some bizarre form of conspiracy. Alternatively, it could be that it simply provides a platform for people looking for a cause to fight because of their personal ideology.

The scientific basis for stating that fluoride in water (at the concentrations recommended) is a safe and very effective approach to improving dental health is clear. Where there is debate, it is with the values-based issues, even though these can be overstated. Sadly, rather than having dialogue on such values issues which is a proper discourse for society, the debate has been hijacked by a misinterpretation of science. Such values debates are critical for a healthy democracy, but they cannot proceed usefully if the debate is shifted inappropriately to another domain.

The Ministry of Health and its expert dental, public health and scientific advisors have been well positioned to opine on the science. Indeed their conclusions are in accord with other major scientific and public health authorities that have looked at the question repeatedly. But irrespective of the conclusions that the scientific community has reached, scientists do not have a privileged position within a values debate beyond clarifying when science is being misused. Such values based debates should focus on any real issues of contention and be resolved through the political process – whether local or nationally.

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