I was lucky enough to be invited on as a guest presenter on The Reality Check, one of Canada’s largest skeptical podcasts. I recorded a couple of shows before I left Ottawa and it was immensely fun and interesting. I had made fairly extensive notes for the segments, and it seemed a shame not to post them here.
For my first official segment (on episode #204), I thought I would go for a simple and uncontroversial topic: water fluoridation. For those of you who are immune to British sarcasm, water fluoridation is a complex and controversial topic, and one that the Reality Check had been promising to cover since about episode #6. I’m going to do my best to provide a background to the topic based on the history of water fluoridation and contemporary research. I’m then going to discuss a recent scientific paper which suggests a possible link between water fluoride levels and reductions in IQ within the context of the wider issues surrounding fluoridation.
I admit that this is mostly from Wikipedia, but the water fluoridation articles there are particularly well referenced so I don’t have a problem with relying upon them. The benefits of the addition of fluoride to the diet has a long history. It was recognised in the 19th Century that fluoride was present in bone, teeth and drinking water, and that particularly high levels of water fluoride was associated with fewer dental health problems. In 1909, Dr Frederick McKay conducted a study of a phenomenon called “Colorado Brown Stain” on almost 3000 children living in the Pikes Peak region of central Colorado. The stain, now known as “dental fluorosis”, was caused by high levels of fluoride and was also associated with fewer cavities .
We knew about the effects of high fluoridation intake from these kinds of studies, with some communities exposed to natural water fluoridation levels of up to 8mg/l. The first clinical trial, comparing newly-fluoridated water in one town (Grand Rapids, Michigan) with unfluoridated water in a comparable, nearby town (Muskegon), began in 1945 and involved 36,400 children. The results demonstrated a marked decline (20-50%, depending on age group and baby vs adult teeth) in dental caries to the point where Muskegon was also fluoridated in 1951, despite the intention to have the study as a long-term trial .
Today, a number of different chemicals are used to introduce fluoride into our water. The USA uses three chemicals: sodium fluoride accounts for 9% of water fluoridation, but is expensive, hexafluorosilicic acid accounts for 63%, and its salt sodium hexafluorosilicate covers the remaining 28%. These latter two chemicals are more common as they are by-products of agricultural fertiliser production . The proportion of citizens receiving fluoridated water varies hugely across the world. Fluoridation is largely confined to English-speaking countries, with 64% of Americans, 44% of Canadians, and 10% of Brits receiving flouridated water. Overall, about 5.3% of the world has artificially fluoridated water, and another 3.4% have access to naturally fluoridated water. However, this is not evenly distributed within each country. For example, within Canada, Nunavut and the Yukon (two northern territories) have no water fluoridation, while Ontario has 76%, Alberta has 75% and Manitoba has 70%. Interestingly, British Colombia and Quebec only have 4% and 6% respectively. Where water is not fluoridated, sometimes fluoridated salt is used, such as in Central Europe.
Opposition to fluoridation has existed since the 1940s, and is still very much around today. Particular points of contention include:
- Violation of human rights – there are passages in various human rights declarations that concern the giving of medicine to people. It can be argued that the engineers who routinely deliver fluoride into the public and private water supplies are not medical professionals and cannot, therefore, act knowledgeably in the best interests of the populace .
- Violation of medical ethics – there is a strong emphasis on showing respect for patient autonomy in medicine. By introducing fluoride into the water supply, “patients” (which in this case means “people who drink water”) have no say in their medication . Responses to this have involved not considering water fluoride as a medicine (UK) and simply not applying medical principles to water fluoridation (US).
- Potential safety risks – As well as specific health problems (one of which I will discuss in a few minutes), there is a general issue with the dispersal of a medicine into a medium that is consumed in different quantities by different individuals. This means that different people are receiving different doses. Furthermore, there is relatively little attempt made to investigate what the effects of the fluoridation are in individuals. There is certainly the potential for dental fluorosis, although keeping levels to the 1mg/l recommended limit makes this a negligible problem. It is easy to dismiss some of these safety problems as being entirely psychosomatic. For example, in the Grand Rapids clinical trial that I mentioned earlier, reports of sore gums and peeling tooth enamel were received by the authorities. One woman even claimed that all her teeth had fallen out. These calls arrived in early January, when some press reports had stated that fluoridation would begin, but some weeks before the actual advent of fluoridation on January 25 . This is a prime example of the nocebo effect, where people perceive illness or pain because they believe that something is happening even when nothing is present that could cause such a reaction. “Nocebo” comes from the Latin “I will harm”.
- Equivocal benefits – There is no doubt that fluoride is good for dental health, and a recent Cochrane review of topical fluoride use (that is, fluoride applied directly to teeth via toothpaste, etc) demonstrated that “The benefits of topical fluorides are firmly established based on a sizeable body of evidence from randomized controlled trials” . On the other hand, a meta-analysis published in the British Medical Journal demonstrated that, while there had been a large number of studies looking at water fluoridation which showed a consistent benefit in terms of reduced cavities and reduced numbers of teeth affected by cavities, the quality of the studies was poor . Also, there have been substantial increases in dental health even in areas without water fluoridation (natural or artificial), simply due to greater awareness of dental health and access to dental health services. This makes it very difficult to evaluate to what extent improvements in dental health are due to fluoridation vs. other mechanisms.
- It’s all just a communist plot – during the “Red Scare” in the 1940s-1960s, the far right in the USA believed that any public health program (including vaccinations, mental health programs and fluoridation) were attempts to establish a communist state by “depleting the brainpower and sapping the strength of a generation of American children”. By the 1960s this conspiracy theory had all but died out and adherents were seen as detrimental to the broader anti-fluoridation movement.
Does Fluoridation Affect IQ?
So the reason that water fluoridation has been in the news a little bit more recently is that a press release was issued by the New York State Coalition Opposed to Fluoridation (NYSCOF) entitled ” Harvard Study Finds Fluoride Lowers IQ – Published in Federal Gov’t Journal”. The press release is based around a paper reviewing evidence for a link between fluoridation and IQ that was published in the journal “Environmental Health Perspectives”, a peer-reviewed open-access medical journal with an impact factor of 6.191 (which means that it is a reasonably well-cited journal). The conclusion of the paper states that “The results support the possibility of an adverse effect of high fluoride exposure on children’s neurodevelopment”. Sounds scary, eh?
However, there are a number of red flags raised by this particular press release:
- While the story featured on major news outlets’ websites (including Reuters), it is a press release by a special interest group and not a news story. As such it has no accompanying commentary.
- Second, the scientific paper describes the actual nature of the study: “Although microbiologically safe, water supplies from small springs or mountain sources created pockets of increased exposures near or within areas of low exposures, thus representing exposure settings close to the ideal, as only the fluoride exposure would differ between nearby neighborhoods. Chinese researchers took advantage of this fact”. In other words, this wasn’t about toothpaste or public health, and it certainly didn’t have anything to do with New York State – the researchers were looking at natural, environmental contamination of drinking water in Chinese communities. But NYSCOF is arguing that this is evidence against artificial fluoridation. Furthermore, the levels used in the study are often an order of magnitude higher than the 1mg/l recommended level, and we always have to bear in mind that these were correlational studies, not experimental studies.
- The press release neglects to mention that the paper discusses the need for the inclusion of additional covariates (such as levels of arsenic and iodine in the water) and the brevity of some of the studies. Some of the papers did not even state which IQ test was used. These were not high-quality studies.
- Finally, the effect size that was detected was very small. In fact, the authors of the paper note that “The estimated decrease in average IQ associated with fluoride exposure based on our analysis may seem small and may be within the measurement error of IQ testing.” We’re talking an average of 0.45 of a standard deviation (around 7 IQ points).
- Water fluoridation is an effective way of improving dental hygiene, but the effect may be limited to those socioeconomic groups that do not have regular access to dental treatment.
- There may be negative effects of fluoride, but these are clinically negligible under the recommended 1mg/l dose. As we often say: the poison is in the dose. Given the extremely low cost (around $1 per person), this remains a highly effective public health intervention, but more research is needed to evaluate the actual benefits in modern society.
- Beware of press releases masquerading as media articles. This is a growing problem, particularly in the reporting of science where precious few journalists have the expertise or the time to properly evaluate what is thrown at them. Check out Mike Marshall’s Bad PR Tumblr for many more examples.
 Dean HT, Arnold FA, Jay P, Knutson JW. Studies on mass control of dental caries through fluoridation of the public water supply. Public Health Rep. 1950;65(43):1403–8.
 R. Allan Freeze and Jay H. Lehr, The Fluoride Wars, (New York, John Wiley & Sons, 2009), 109
False teeth image by Håkan Svensson
Dental fluorosis image by josconklin