Community Water Fluoridation: Open Discussions Strengthen Public Health

In 2015, AJPH published two articles on issues related to community water fluoridation (CWF). CWF consists in feeding a fluoride compound into the water supply of a community up to a desired concentration, usually one milligram per liter, so that everyone who drinks tap water gets some fluoride. The idea appeared last century with the purpose of mass prevention of dental caries. Fluoride protects the teeth probably by interfering with the metabolism of bacteria causing caries. CWF is used by millions of people worldwide and in 1992 reached 144 million people in the United States.¹ I have not found more recent statistics.

When millions of people are exposed to some preventive measure, the immediate reaction of the public health professional is to wonder if the benefit is worth the risk because even a small risk applied to so many people could have dramatic consequences.

Assessing the impact of a small risk requires epidemiological comparisons. And here is where the situation gets complicated. The consensus about the protective effect of fluoride on tooth carries and its lack of toxicity at optimal concentrations is such that fluoride has been very widely prescribed to children as pills and can be found in many toothpastes. Pure comparisons of people exposed to CWF over sufficiently long periods of time and at crucial ages with people not exposed to fluoride have become impossible.

The impossibility of observing clear-cut evidence in one direction or the other has created an ideal situation for intricate controversies. People who believe that fluoride is dangerous for children’s health disseminate imaginary suspicions against CWF, and look for every weakness in epidemiological studies contradicting their views to denigrate the evidence. On the other side, the advocates for CWF, who rely on the extensive evidence of the beneficial effects and lack of harm of CWF, have been so scolded by the anti-CWF propaganda that they tend to see enemies in everyone who does not adhere entirely to their defense line. In the process, AJPH becomes the ring in which some of these fights take place. When AJPH publishes an article supporting CWF, letters pour in from the antifluoridation camp criticizing it. When AJPH publishes an article that does not unconditionally support CWF or its glorious history, inflamed letters vituperate a supposed alignment on the side of the public health enemy. Year 2015 was a case in point.

In the first of these 2015 articles, Broadbent et al. indicated that CWF was not deleterious for the development of intelligence.^2,3 The average IQ in some New Zealand communities with CWF was similar to that in communities without CWF. The authors have taken as much advantage as possible of a longitudinal study with repeated measurements of IQ. The study has methodological limitations, like all cohort studies, but it is undoubtedly a rigorous contribution to the literature. The anti-CWF camp, represented in the following letter by Osmunson et al.,⁴ was prompt to notice that the reference group was not pure. They argue that because everyone in the compared communities has been exposed to some fluoride, either in the water, in pills, or in toothpaste, the IQs of all the New Zealanders involved in the comparisons has already been eroded by fluoride in one way or another, implying a weakened quasi-experimental design in which no valid differences can be found anymore. Wrong. As explained in the response by Broadbent et al,⁵ there is sufficient variability in overall fluoride intake to perform meaningful comparisons.

In the second of these 2015 articles, historian Carstairs^6,7 revisited the conditions in which CWF began to be adopted on a large scale in the early 1950s. She makes three claims: (1) scientists and dentists were not unanimous in supporting CWF, (2) early concerns about the toxicity of fluoride were put aside, and (3) little money was spent on fluoridation research after the 1950s and it was of “poor quality.” Whether one agrees or not with these statements, they can be empirically verified.

Carstairs’s first point is a given. That scientists were divided on such issues is not surprising; indeed, the contrary would have been. On the second point, Newbrun⁸ and Friedman⁹ contest that some concerns were put aside by the proponents of CWF. In my view, Carstairs’s detailed analysis of the concerns of those who did not embrace CWF convincingly shows that these arguments were too vague to weigh in the policy decision. Let’s review this question. Imagine it’s 1951 and you have to decide whether to implement CWF in your community. You open the last issue of the American Journal of Public Health and, in favor of CWF you have the evidence from the Newburgh-Kingston, New York, study.¹⁰ In 1942, the question of whether fluoridation was beneficial was sufficiently unsettled for the City Council of Kingston to decide to continue to use its fluoride-deficient supply for the purpose of serving as control to a fluoridation experiment in Newburgh, situated 35 miles away along the Hudson River.¹¹ Eight years later in 1950, there was substantial population evidence that naturally high levels of water fluoridation were inversely correlated with dental caries and that artificial fluoridation reduced the incidence of caries in a population.¹² The Newburgh-Kingston experiment for which final report was published in 1956, included an extensive evaluation of possible effects of fluoridation on child growth, maturation, cancer, etc.¹¹ On the other hand, against CWF, you would have listened to the opponents cited by Carstairs who expressed “concerns” about the long-term or environmental effects of CWF, sometimes backed by studies on rats. They had no evidence based on population studies in humans to support their beliefs. It is therefore unlikely that these opponents would have modified your decision about whether to implement CWF in your community. However, the “concerns” may have affected the amount and quality of research that could have been supported after that. This brings us to the third of Carstairs’ points. In their systematic review, McDonagh et al.¹³ concludes that the quality of the evidence is low, maybe for the reasons Carstairs has explained.^6,7 However, it does not contradict any of the knowledge on the benefits or harms of CWF.

The controversy about CWF will not end with these exchanges. In 1951 Hillboe and Ast, respectively, Commissioner and Director of the Bureau of Dental Health in New York City, prophetically stated in the American Journal of Public Health that

It is not surprising that some individuals are still questioning the safety factor. Fifty years from today when water fluoridation probably will be an accepted and routine public health practice there may still be some who will question it just as there are those today who question water purification through chlorination.^10(p1372)

As in the case of vaccines, public health will continue to suffer from the dissemination of absurd beliefs about unfounded risks, putting the whole community (but even more so the most disadvantaged) at risk for tooth decay or of preventable infectious outbreaks. But we will not give up the freedom to discuss inconvenient ideas because of them. AJPH will continue to publish strong pieces of research even when they do not fit well with our preconceived ideas. AJPH will also publish the opinions of those who disagree. Open discussions strengthen public health.