Four questions to ask when reading or writing about water fluoridation and IQ

Kevin Lomangino is the managing editor of He tweets as @KLomangino.

Multiple news outlets are covering a new study conducted in Mexico on fluoride exposure during pregnancy and its association with lower childhood IQ.

Water fluoridation is common across the U.S. and the potential to stoke unwarranted fear is great. If you are reading or writing about this study, here are four questions you should be asking yourself:

Does the headline overstate the evidence?

This was an observational study that can only show associations between fluoride and IQ — not that fluoride exposure caused a change in IQ. Newsweek’s headline — “CHILDREN’S IQ COULD BE LOWERED BY MOTHERS DRINKING TAP WATER WHILE PREGNANT” — goes beyond what the study can tell us, as does Readers Digest’s “If You Drink This Type of Water During Pregnancy, Your Child’s IQ Could Suffer.”

Remember: If fluoride “could” cause these problems it just as easily “could not” cause them.

It’s impossible, based on the results of this one study, to know if fluoride “lowered” IQ or whether children with lower IQ in Mexico are simply more likely to have higher fluoride levels for some unknown reason. CNN gets it right with “Fluoride exposure in utero linked to lower IQ in kids, study says.” Canada’s National Post also nails it with  “Researchers urge caution over study linking fluoride exposure in pregnancy to lower IQs in children.”

Learn more by reading our primer: Observational studies: Does the language fit the evidence? Association vs. causation 

Does the story discuss the limitations of the research?

The study authors describe a long list of items that could have influenced their results, including the methods they used to collect urine samples (one-time collection rather than the more rigorous 24-hour method) and lack of information about other factors (e.g. exposure to neurotoxins like arsenic) that might impact childhood cognition. They also don’t know how the mothers in the study were exposed to fluoride or at what levels. In addition, they said, “we cannot rule out the potential for uncontrolled confounding due to other factors, including diet, that may affect urinary fluoride excretion and that may be related to cognition.”

The other point to consider is that this is a single study conducted in an area that doesn’t have fluoridated water and which might not reflect U.S. circumstances. As CNN appropriately observes, “a study done in New Zealand, a country that has community water fluoridation similar to the United States, found no connection between fluoridated water and IQ.”

Does the story explain the size of the effect?

This is an area where all of the stories I read could have done better. The researchers reported a drop of 2.5 IQ points for every 0.5 mg/dL increase in fluoride levels (average fluoride levels in these children were around 0.8 mg/dL). Obviously, any association of fluoride with reduced cognition is worrisome, but it’s important to get specific. Is a 2.5-point difference meaningful or even noticeable? None of the stories explained. Susan Molchan, MD, a psychiatrist and former NIH researcher, said “2.5 points is probably not enough to make a difference in school performance for example when you consider the range of a normal IQ would be 90-110. What’s the difference if you’re 100 or 97.5? And how one performs on an IQ test is just one small piece of how one will do in school/life—so it is a good question on how clinically or functionally significant this is.”

Does the story explain the potential benefits of water fluoridation?

CNN repeated the CDC’s claim that water fluoridation is “one of the 10 greatest public health achievements of the past century.” CTV said that water fluoridation should be acknowledged as “a public health success story.” But none of the stories dug into the evidence supporting these claims, much of which comes from observational studies conducted before 1975. Just as these types of studies can’t definitively prove harm from fluoridated water, they can’t prove definitively that water fluoridation caused reductions in cavities. In fact, many didn’t account for circumstances that have clear potential to impact the effectiveness of fluoridated water — for example the introduction of fluoride toothpaste or the amount of sugar consumed by study participants. A recent systematic review of the evidence conducted by the Cochrane Collaboration found no evidence that fluoridation reduces cavities in adults and very limited evidence for a benefit in children.

There is very little contemporary evidence, meeting the review’s inclusion criteria, that has evaluated the effectiveness of water fluoridation for the prevention of caries. The available data come predominantly from studies conducted prior to 1975, and indicate that water fluoridation is effective at reducing caries levels in both deciduous and permanent dentition in children. Our confidence in the size of the effect estimates is limited by the observational nature of the study designs, the high risk of bias within the studies and, importantly, the applicability of the evidence to current lifestyles.

The Cochrane authors point out that cross-sectional studies — considered a lower form of evidence because they only examine data at a single time point — have been conducted more recently but were excluded from their analysis. They also acknowledge that it may be difficult or impossible to obtain gold-standard clinical trial evidence demonstrating the benefits of water fluoridation. The practical obstacles to conducting such studies are significant. Nonetheless, they say that more contemporary studies, with more rigorous designs, and needed to determine whether water fluoridation is beneficial under current circumstances and to what extent.

How to help readers navigate uncertainty

Sometimes mountains of observational data are enough to guide sound public health recommendations and action. Observational studies documenting the harms of tobacco are an example of this. Still, the four questions raised in this piece are important for journalists and the public to consider.

Molchan believes the emerging data should prompt reflection about community fluoridation policies. “Why go through the expense of adding a chemical to the whole water supply if there is no known benefit, especially if there are questions about its safety?” she asks.

That seems to be theme running through this entire topic: questions, but few answers, on the benefits and risks of water fluoridation. Journalists who explore these questions carefully will help readers understand what’s at stake without spreading needless fear.

Note: We’ve previously examined coverage of research linking fluoride in water with attention deficit hyperactivity disorder.

You might also like

Comments (6)

Please note, comments are no longer published through this website. All previously made comments are still archived and available for viewing through select posts.

James Reeves

September 22, 2017 at 8:30 pm

Other studies also show the destructive effects of fluoride on brains.
Here is what Harvard researcher Philippe Grandjean had to say: “Fluoride seems to fit in with lead, mercury, and other poisons that cause chemical brain drain,” Grandjean says. “The effect of each toxicant may seem small, but the combined damage on a population scale can be serious, especially because the brain power of the next generation is crucial to all of us.”

Ken Perrott

September 23, 2017 at 12:55 am

Thanks for this.

I have also made a critique of the actual study reported. In fact, it explains only about 3% of the variation in child’s IQ – and may not explain any of the variation once more important risk-modifying factors are included in the analysis.

Carol Kopf

September 23, 2017 at 4:26 am

About the one hour vs 24 hour urine collection, the authors write, “others have noted a close relationship between the fluoride concentrations of early morning samples and 24-hr specimens (Watanabe et al. 1994; Zohouri et al. 2006)”

This study didn’t measure fluoride intake. It measured urine fluoride levels which is a reflection of fluoride intake from all sources – water, salt, dental products, air pollution, food. The urine fluoride levels found in pregnant Mexican women are similar to urine fluoride levels reported in healthy American adults who live in fluoridated areas.

Once fluoride is ingested or absorbed into the bloodstream, it is all the same in terms of toxic effects on the fetus. The developing brain in the fetus can’t tell which source the fluoride came from.

The lead researcher, Dr. Howard Hu is quoted as saying ““This is a very rigorous epidemiology study. You just can’t deny it. It’s directly related to whether fluoride is a risk for the neurodevelopment of children. So, to say it has no relevance to the folks in the US, seems disingenuous.”

The New Zealand study (Broadbent) is scientifically invalid for several reasons – the most important was that it measured populations that had similar fluoride intakes – one from a fluoridated area and the other from a non-fluoridated area but where fluoride supplementation prescriptions are common.

This new careful investigation, by respected researchers from respected institutions and published in a respected peer-reviewed journal, adds to a frightening trend. Over 300 studies now link fluoride to neurotoxic effects – 50 of them human – over 20 at fluoride levels allowed in US water supplies. Taken together, with this new study, the evidence is now very strong that fluoride exposures common in the USA is causing IQ loss in at least some children

The loss of IQ is very large. The child of a mother who was drinking 1 ppm fluoride water would be predicted to have 5 to 6 IQ points lower than if the mother had drunk water with close to zero fluoride in it… Such a drop of IQ in the whole population would half the number of very bright children (IQ greater than 130) and double the number of mentally handicapped (IQ less than 70)

When fluoridation began in 1945, there was no thought that fluoride could get into the brain where it doesn’t belong. That fact is now indisputable. Even the EPA reports fluoride is neurotoxic. We shouldn’t have to wait to find out how much damages our brains to spare one cavity. Fluoride on the brain should be the death knell for fluoridation if organized dentistry’s political power didn’t have a heavy hand in pressuring legislators to retain fluoridation.

Janet Nagel

September 23, 2017 at 5:00 pm

This human study is just the latest one to address fluoride neurotoxicity and it confirms dozens of human studies done in India, China, and elsewhere that confirm a link between fluoride exposure and neurological injury. The question that readers should be asking is why all the efforts to dismiss the significance of the study by fluoridation proponents, and the unprofessional advice to pregnant women to disregard the results of the study?
The even bigger question is why does non-consensual fluoride treatment continue to be done in the US when the CDC declared 18 years ago that swallowing fluoride does not confer resistance to tooth decay, making the purpose of fluoridation invalid? –See Achievements in Public Health, 1900-1999: Fluoridation of Drinking Water to Prevent Dental Caries. Morbidity and Mortality Weekly Report 48: 933-940
Non-consensual fluoride treatment is a violation of human and constitutional rights for no legitimate purpose.–See Nuremberg Code, UNESCO Universal Declaration on Bioethics and Human Rights, and Highlights in North American Litigation During the Twentieth Century on Fluoridation of Public Water Supplies, by JR Graham & P Marin, J. Land Use and Envtl. Law, Vol 14:2 (Spring 1999)
Attention pregnant women and everyone else: Fluoride does not belong in your water and all the drinks and foods made with that water. Infants drinking milk formula made with fluoridated water get a disproportionately large harmful daily dose of fluoride. This latest fluoride-IQ study confirms for the umpteenth time that fluoridation is a pointless public health travesty.
Project TENDR–Targeting Environmental Neuro-Developmental Risks 2016 Report:
“We as a society should be able to take protective action when scientific evidence indicates a chemical is of concern, and not wait for unequivocal proof that a chemical is causing harm to our children.”

john Teagle

September 23, 2017 at 6:24 pm

The precautionary principle should apply where is any evidence of harm unless it can be proven .scientifically to be other wise. Australia is the most fluoridated country in the world and we have a serious problem with children falling behind even third world countries when it comes to education.

Bill Osmunson DDS MPH

September 24, 2017 at 10:14 am

[Editor’s note: In response to our queries, the author of this comment has supplied references to support the claims made in the comment. These are appended to the bottom of the comment. has not reviewed or verified the veracity of the claims.]

Over 300 studies confirm, ingesting fluoride is not safe.
The latest study by Bashah et al, is one of the strongest and confirms loss of IQ at very small amounts of fluoride. The urine fluoride concentrations of mothers in the study resulting in harm is similar to mothers in fluoridated communities.
Promoters of fluoride ingestion require the highest level of confidence and would not speak against fluoride even if God were to speak from heaven with numerous randomized controlled trials finding harm.
Yet when they talk about “benefit,” they accept low quality historic studies which have numerous flaws. As a dentist, the hardest part for me to accept is the Food and Drug Administration’s finding that the evidence of effectiveness is “incomplete.”
The FDA says, “Do Not Swallow.”
The FDA says, the evidence of effectiveness is “incomplete.”
The EPA says about a third of children after the age of six months are ingesting too much fluoride.
HHS recommends lowering fluoride concentration in water because many are ingesting too much fluoride.
Most developed countries do not support adding fluoride to any water or salt.
Dosage of fluoride for the individual is not controlled because the amount of water is not controlled.
The latest study by Bashah reporting lower IQ for the fetus means fluoridated water is not safe for the fetus.

Here are references and evidence for your questions.

A. The FDA says, the evidence of effectiveness is “incomplete.”

1. “. . .there is no substantial evidence of drug effectiveness as prescribed, recommended or suggested in its labeling. . . marketing is in violation of the new drug provisions of the Federal Food, Drug, and Cosmetic Act; they have, therefore, requested that marketing of these products be discontinued.” FDA Letter to 35 Companies DRUG THERAPY 1975

2. Do a search of FDA’s approved drugs, Orange Book. Fluoride for ingestion is not approved. Topical is approved, toothpaste, with the warning not to swallow.

3. A careful read of the FDA NDA finds drugs which are not approved are illegal drugs. The FD&C Act defines drugs as “substances used with the intent to . . . prevent disease.” The FDA testified to Congress that fluoride is a drug. The fluoride toothpaste label says, “Drug Facts”

B. The EPA says about a third of children after the age of six months are ingesting too much fluoride.

The graph below is from the EPA’s 2010 Exposure and Relative Source Contribution Analysis, Figure 8-1. This document is in response to the NRC 2006 review of EPA’s MCLG where the National Research Council informed the EPA that their CONTAMINANT level for fluoride was not protective and the EPA needed to do a New Dose Response Analysis and Exposure and Relative Source Contribution Analysis. Four years later, the EPA came out with both documents and 7 years later (11 years after the NRC report) the EPA has still not lowered the MCLG to protect the public.

Editor’s note: The referenced graph can be viewed here.

1. The percentage of children above the black line are ingesting too much fluoride.
2. The EPA only includes the public to the 90th percentile. 10% of the public drinking the most water are not on the graph.
3. The EPA does not include those under six months of age on formula made with fluoridated water, all would be ingesting too much fluoride.
4. Instead of making the MCLG more protective, the EPA is doing the opposite, claiming fluoride is safer than before by proposing to INCREASE the RfD from 0.06 mg/kg/day to 0.08 mg/kg/day. . . a 33% increase.

C. HHS recommends lowering fluoride concentration in water because many are ingesting too much fluoride.

Federal Register A Notice by the Health and Human Services Department on 05/01/2015

From the Summary:

“For these community water systems that add fluoride, PHS now recommends an optimal fluoride concentration of 0.7 milligrams/liter (mg/L). In this guidance, the optimal concentration of fluoride in drinking water is the concentration that provides the best balance of protection from dental caries while limiting the risk of dental fluorosis. The earlier PHS recommendation for fluoride concentrations was based on outdoor air temperature of geographic areas and ranged from 0.7-1.2 mg/L. This updated guidance is intended to apply to community water systems that currently fluoridate or that will initiate fluoridation, and is based on considerations that include:

Scientific evidence related to the effectiveness of water fluoridation in caries prevention and control across all age groups,
Fluoride in drinking water as one of several available fluoride sources,
Trends in the prevalence and severity of dental fluorosis, and
Current evidence on fluid intake of children across various outdoor air temperatures.”

As a sample, is one of 300 studies reporting harm to the developing brain. Thyroid, bones, cancer are other areas you should consider.