Will Fluoridated Water Lower My Child’s IQ?
A couple of weeks ago, my husband sent me a link to a Reuters press release with the following title:
Husband and I have been interested in the fluoride controversy since we moved to Eugene, OR about a year ago. Our municipal water is not fluoridated, and natural levels are very low. Husband confirmed this when he called the water company to get their latest data on mineral composition in our city water. He makes his own beer, so these things matter to him on more than one level. Because our water is so low in fluoride and BabyC has a family history of tooth decay (me), we give her the pediatrician-recommended fluoride supplement. You can check the fluoride levels in your water supply using this CDC resource or contact your water company for what is likely a more up-to-date and accurate number.
Anyway, I keep seeing this story about fluoride and IQ posted on FB and other sites around the Internet, so I thought it was worth addressing in a blog post. Naturally, we parents worry about these things. Fluoride lowers children’s IQ? Yikes! What parents would knowingly give their child something that does that? And try to do a little research online about fluoride safety and you’ll find a range of “resources,” most of them with scary headlines like the one above.
Well, there are all sorts of problems with making decisions about your child’s health based on what you read on the Internet, and this story makes a very good case study. Let’s take a closer look.
Before we even get into the science, a quick reading of the press release itself raises some red flags. Here’s the first paragraph:
“Harvard University researchers’ review of fluoride/brain studies concludes “our results support the possibility of adverse effects of fluoride exposures on children’s neurodevelopment.” It was published online July 20 in Environmental Health Perspectives, a US National Institute of Environmental Health Sciences’ journal (1), reports the NYS Coalition Opposed to Fluoridation, Inc. (NYSCOF).”
There are some signs of credible research here. The study was done at Harvard, and it was published in a peer-reviewed journal. There is even a link to the full-text article . However, the quote from the paper is a little less dramatic than the headline – their results “support the possibility…” of said scary effect.
But the real issue comes in that last line. The results of this study are not being reported by the study authors or Harvard but by NYSCOF – an anti-fluoride advocacy group. They wrote the press release – it says so at the bottom of the page. In other words, the press release contains NYSCOF’s analysis, opinions, and yes, spin, on this study. This is never a good sign – at least not if you are looking for accurate information.
The press release goes on to quote the president of NYSCOF and to state that low doses of fluoride are harmful to babies. If you forgot to put on your media-savvy cap before reading the piece, you’d walk away thinking that water fluoridation is poisoning our babies, so says Harvard researchers in a “Federal Gov’t Journal!”
So the press release is suspect, to say the least. Let’s lose the spin and take a look at the science.
Anna Choi, the lead author of the study, is a research scientist at Harvard’s School of Public Health. Her previous work has focused on toxicity of mercury and organochlorine contaminants. Other study authors included two from China Medical University.
The study is actually a meta-analysis of 27 previously published studies looking for correlations between children’s intelligence and fluoride exposure. These were cross-sectional studies measuring children’s IQ at one point in time and comparing scores between low versus high fluoride areas. The meta-analysis used statistical methods to summarize the average difference in children’s IQ associated with fluoride exposure.
Both the National Research Council (NRC)  and the WHO  have recently reviewed the relationship between fluoride exposure and intelligence. What makes this current review different is that it includes many studies from rural China, which were not evaluated in the previous analyses. All but two of the included studies were conducted in China, with the remaining two being from Iran.
Why are there so many studies on fluoride in China? There are not municipal artificial fluoridation programs in China as there are in the U.S. Instead, it turns out that China has large veins of naturally occurring fluoride in the water table such that some areas have very high levels of fluoride while their neighbors do not. According to the paper,
“Chinese researchers took advantage of this fact and published their findings, though mainly in Chinese journals, and according to the standards of science at the time. This research dates back to the 1980s, but has not been widely cited at least in part because of limited access to Chinese journals.”
In their meta-analysis, Choi et al. found a small but consistent and significant relationship between water fluoride concentrations and children’s IQ scores. Those living in the high fluoride areas scored about 0.4 points (standardized weighted mean difference, SMD) lower than those living in the low fluoride areas. When they excluded studies that included co-exposures to arsenic and iodine and to fluoride from coal burning, leaving only 9 studies, the IQ differential dropped to 0.29 points (SMD), though it was still significant.
Before we can judge the relevance of these data, however, we need to know how the Chinese studies defined high and low fluoride. The high fluoride areas had anywhere from 1 mg/L to 11 mg/L of fluoride, while the low fluoride areas had less than 1 mg/L fluoride in their drinking water.
Let’s put that in context. By these standards, most towns in the U.S. have low fluoride in their water. The U.S. Department of Health and Human Services (HHS) currently recommends that in areas without naturally occurring fluoride, it should be added to water supplies to a concentration of 0.7 mg/L. (My daughter’s daily dose of 0.25 mg of fluoride provides about the same amount as if she was drinking water with this concentration.)
In 2000, it was estimated that 162 million Americans had artificially fluoridated water containing 0.7-1.2 mg/L. Fluoride concentrations are more variable in areas with naturally high levels. 1992 data estimated that 10 million people in the U.S. have naturally fluoridated water. Of these, most have low concentrations, but 19% have greater than 2.0 mg/L, the concentration at which some research suggests that we should be concerned . Some areas are naturally very rich in fluoride – concentrations have been measured as high as 13 mg/L in parts of New Mexico and 15.9 mg/L in Idaho.
Take a look at fluoride concentrations in many different sources of water in U.S. You’ll see that the highest concentrations of fluoride are found in municipal water that is naturally fluoridated and in well water.Source: 2006 NRC Report .
Back to the recent Harvard meta-analysis: My interpretation of the study is that fluoride may have a small effect on children’s IQ when present at very high concentrations. This isn’t surprising. Most chemicals, including other minerals and vitamins can be toxic if present in high enough amounts. Illustrating this, Choi et al. cite a study  showing that when rat hippocampal neurons were incubated in a petri dish with 20-80 mg/L of fluoride, there were signs of toxicity in those neurons. If you are a rat, and you are bathing your brain in high concentrations of fluoride, you should be very concerned. However, if you are bathing in municipal water with less than 2 mg/L of fluoride, I’d recommend pouring in some bubble bath and soaking a little longer.
There were a few other problems with the study to consider. First, the data only show a correlation between intelligence scores and community fluoride concentrations. There is no evidence for a causal relationship, and any number of other factors could contribute to these observations. Furthermore, the meta-analysis did not account for important factors such as parental intelligence or socioeconomic level. These factors do influence children’s IQ, and they could vary based on geographical area just as do naturally occurring fluoride concentrations. Also, the reported IQ difference is very small and may be within the error of measurement.
Finally, we don’t know anything about the quality of the Chinese studies or the peer review process under which they were published, except what the authors tell us:
“…each of the articles reviewed had deficiencies, in some cases rather serious, which limit the conclusions that can be drawn. However, most deficiencies relate to the reporting, where key information was missing. The fact that some aspects of the study were not reported limits the extent to which the available reports allow a firm conclusion.”
I should point out that while I see plenty of problems with using the results of this study to criticize water fluoridation or to incite fear in the hearts of parents, I don’t think that the study itself is entirely meaningless. The authors are fair in their assessment of the study’s importance:
“Although the studies were generally of insufficient quality, the consistency of their findings adds support to existing evidence of fluoride-associated cognitive deficits, and suggests that potential developmental neurotoxicity of fluoride should be a high research priority.”
The 2006 NRC report  on fluoride in drinking water, written by a committee of experts in toxicology and dentistry, reviewed some of the same studies and reached a similar conclusion. This 531-page report (available online if you are looking for some light reading) also reviewed a range of other concerns about fluoride exposure. It is generally very careful and conservative in tone, making note of concerning research but not jumping to alarmist conclusions. It is critical of the EPA’s fluoride limits and ultimately recommends that they lower their Maximum-Contaminant-Level Goal (MCLG) from 4 mg/L to 2 mg/L.
So yes, let’s do more research. In the meantime, there is no evidence that we should be concerned about fluoride impacting our children’s chances at getting into Harvard. An exception is for families living in areas where fluoride naturally exceeds 4 or maybe even 2 mg/L. If you aren’t sure about the fluoride concentration of your municipal water, it is worth a check. If you drink water from a private well, you should have it analyzed to check for fluoride as well as other metals.
P.S. – After looking into the accuracy of that Reuters press release, all I could do was wonder what it takes to get them to put your press release on their website. They don’t appear to have very stringent standards, and there is some very fine, light gray print below the title of the article reading, “*Reuters is not responsible for the content in this press release.” I should start submitting press releases to Reuters with a link back to my website, just like NYSCOF. It’s great advertising. The problem is that nowhere on the page does it say that the article is an ad. Furthermore, the comments are closed, so there is no chance for a knowledgeable reader to contest the information in the article.
1. Choi, A.L., et al., Developmental Fluoride Neurotoxicity: A Systematic Review and Meta-Analysis. Environ Health Perspect, 2012.
2. Committee on Fluoride in Drinking Water – National Research Council, Fluoride in Drinking Water: A Scientific Review of EPA’s Standards, 2006, The National Academies Press: Washington, DC.
3. World Health Organization, Fluoride in Drinking Water, 2006, World Health Organization. p. 144 pp.
4. Zhang, M., et al., Effects of fluoride on DNA damage, S-phase cell-cycle arrest and the expression of NF-kappaB in primary cultured rat hippocampal neurons. Toxicol Lett, 2008. 179(1): p. 1-5.