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There is a movement in the US to oppose a public health measure that is backed by impressive evidence showing it is safe and effective, as well as highly cost effective. For as long as the government has supported this health measure, there have been those opposed to it, claiming (against the evidence) that it is unsafe, ineffective, and represents a violation of personal freedom and the right to refuse an unwanted medical intervention. I could be talking about vaccines and the anti-vaccine movement, but in this case I am talking about the fluoridation of public water supplies and the antifluoridation movement.

This social debate (there isn’t much of a scientific debate) crops up in the news every now and then – mostly prompted by an antifluoridation activist or group making noise, or by a local referendum to block fluoridation in a community. Recently there has been a Harvard study making the rounds of social media, “Developmental Fluoride Neurotoxicity: A Systematic Review and Meta-Analysis.” The actual findings of the study do not show that there is any risk to public water fluoridation (if anything, they show that it is safe), but the study was seized upon by antifluoridation activists and distorted for their propaganda purposes. Unfortunately, the internet is now fertile ground for the spreading of propaganda.

The NYS Coalition Opposed to Fluoridation put out a press release distorting the findings of the study. Their press release (“Harvard Study Finds Fluoride Lowers IQ – Published in Federal Gov’t Journal”) was then printed as a science news item by many online news outlets. Reprinting press releases, without any editorial filter, is a cheap and easy way to add news-like content to your website. The Sacramento Bee, for example, published the press release under their “News” tab. Near the top of the page, in small print, they did put a disclaimer (which is better than most sites):

This section contains unedited press releases distributed by PR Newswire. These releases reflect the views of the issuing entity and are not reviewed or edited by the Sacramento Bee staff. More information on PR Newswire can be found on their web site.

That’s better than nothing, but I wonder how many people reading the press release will notice and read the disclaimer. In my opinion, a news outlet should not reprint press releases sent out from advocacy organizations clearly intended to promote an agenda. They especially should not print them under the banner of “News.” The disclaimer is not adequate. The spreading of this “news item” around Facebook and other social media demonstrates this.

Some background

Before I get to the study itself, let me review the basic facts surrounding fluoridation of public water supplies. In the 1940s and 50s in the US there were major studies looking at the role of fluoride in the health of teeth. It was first noticed that too much fluoride, which occurs naturally in many water supplies, can cause a darkening and pitting of the teeth, now called fluorosis. However, smaller amounts of fluoride are necessary for tooth health and can help reduce tooth decay. Fluoride can help remineralize the enamel of teeth, to reduce or even reverse destruction by acid-producing bacteria.

The turning point in terms of evidence came with the publication of a study in 1950 – Dr. H. Trendley Dean, head of the Dental Hygiene Unit at the National Institute of Health published the results of a study in Grand Rapids, Michigan in which fluoride was added to the drinking water of one community and not another. The study revealed a 50% decrease in dental cavities in the fluoridated community compared to the control. This and other evidence led to the recommendation to adjust the fluoride levels of local water supplies to about 1 mg/L (or 1 part per million, ppm). Some communities have natural levels of fluoride in the water at higher levels, and these are often reduced. The decision on whether and how to adjust fluoride is made at the municipal and local governmental level – not the Federal level. Therefore, some communities add fluoride while others do not.

Immediately after the recommendation was made and some communities started adding fluoride, the antifluoridation movement started. The primary motivation seems to be objecting to the imposition on personal freedom, seeing fluoridation as involuntary medication. Groups that oppose fluoridation, however, are typically not content to make the freedom argument, but rather also distort the evidence to argue that fluoridation is not safe or effective, despite the actual evidence. At the fringe there are also those who believe that the fluoridation of water is part of a dark government conspiracy to make us all into mindless slaves. (These conspiracy theories were famously lampooned in the brilliant movie Dr. Stranglove, when the character General Jack Ripper talks about the violation of his “precious bodily fluids.”)

The last 50 years of scientific research has only confirmed the safety and efficacy of fluoridation. A 2008 systematic review of this research concluded:

Fluoridation of drinking water remains the most effective and socially equitable means of achieving community-wide exposure to the caries prevention effects of fluoride. It is recommended that water be fluoridated in the target range of 0.6-1.1 mg/l, depending on the climate, to balance reduction of dental caries and occurrence of dental fluorosis.

For further background see the policy statement on fluoridation by the Institute for Science in Medicine (of which I and other SBM authors are members).

The Harvard study

The Harvard study is actually not a new study, but a review of prior research. Further, the studies reviewed did not involve water fluoridation programs.  The review concludes:

“The results support the possibility of an adverse effect of high fluoride exposure on children’s neurodevelopment. Future research should include detailed individual-level information on prenatal exposure, neurobehavioral performance, and covariates for adjustment.”

“The possibility” of an effect justifying future research is not the same as concluding that there is an effect. But the problems with the way this review is being presented go far deeper. The implication being implied by anti-fluoride groups is that the fluoridation program in the US and elsewhere is putting children’s IQs at risk. This data, however, cannot be used to support that conclusion.

First it should be noted that almost all of the studies reviewed were conducted in China (one was conducted in Iran) – not in the US. China had a limited fluoridation program for a time, and has had no fluoridation of drinking water since 2002. So why, then, are most of the studies from China?

There are many rural areas of China that have naturally high levels of fluoride in the well water. The studies were largely looking at this exposure. Two studies looked at fluoride exposure from inhaling smoke from coal burning. So the question is – how do these levels of exposure relate to the amount of fluoride being added to water in the US (because toxicity is always all about dose)? There was a lot of variability across the studies, but generally the high fluoride groups were in the 2-10 mg/L range, while the reference low fluoride groups were in the 0.5-1.0 mg/L range (not including the coal burning studies, which had much higher fluoride levels).

The recommended fluoride level for fluoridated drinking water is 0.5-1.0 mg/L (similar in most countries – Australia, for example, uses 0.6-1.1 mg/L). The EPA set the upper safe limit at 4.0, with a secondary (voluntary) recommendation of 2.0. Areas with high natural fluoride actually have some of the fluoride removed from the drinking water.

In other words – fluoridated water in the US has the same level of fluoride as the control or low fluoride groups in the China studies reviewed in the recent article, and the negative association with IQ was only found where fluoride levels were much higher – generally above EPA limits.

Also – these studies were mostly epidemiological or ecological – they were not experimental studies (like the Grand Rapids study) in which variables were controlled in any way. It is possible, and even likely, that the high levels of fluoride exposure from natural or industrial sources (not deliberate fluoridation) also correlate with exposure to other contaminants, such as arsenic.

Conclusion: Your drinking water is still safe

There are many weaknesses to the epidemiological studies reviewed in the recent article – high heterogeneity, poor controlling for other variables, no indication of blinding of IQ assessments, and many others. But even taken at face value they do not indicate any association between lower IQ and the fluoride levels added to drinking water in the US. In fact, those levels of fluoride were used as the controls in these studies showing higher IQ. (There was a lot of variance of the effect size, but the net effect size on IQ in the meta-analysis was -0.45 standard deviations). Therefore, if anything, this review adds to the body of evidence for the safety of fluoridation.

This fact has not stopped anti-fluoridation groups from exploiting the review for their own propaganda purposes. Otherwise respectable news outlets are unwittingly collaborating in this anti-scientific propaganda campaign by lazily reprinting these press releases in their news sections – without any editorial filter.

The “fluoride wars” are likely to continue as long there is a fluoridation program. This is evidence that there is no public safety measure that is so effective, safe, and cost effective that there will not be those who vigorously oppose its implementation.


Posted by Steven Novella

Founder and currently Executive Editor of Science-Based Medicine Steven Novella, MD is an academic clinical neurologist at the Yale University School of Medicine. He is also the host and producer of the popular weekly science podcast, The Skeptics’ Guide to the Universe, and the author of the NeuroLogicaBlog, a daily blog that covers news and issues in neuroscience, but also general science, scientific skepticism, philosophy of science, critical thinking, and the intersection of science with the media and society. Dr. Novella also has produced two courses with The Great Courses, and published a book on critical thinking - also called The Skeptics Guide to the Universe.