Fluoride Linked to Lower IQ: New Study

A new study has linked pregnant women’s fluoride consumption from drinking water with lowered IQ in their male children.  Though this federally-funded, longitudinal study appears carefully controlled, because it can potentially affect public policy, as well as corporate interests, the results are being hailed as highly controversial–so much so that the study’s methodology and the conclusions by the scientists who authored it have undergone an unusually high level of scrutiny by the medical journal prior to publication of the results and the published study is accompanied by a special note from the journal’s editor outlining the abundance of caution that was used in the peer-review and editorial processes.


Based on the results of public experiments that began with a 1945 pilot study indicating a link between fluoride and reduced tooth decay, the U.S. began putting fluoride in the drinking water.  The public experiments that ran in cities from around the globe until the late 1950’s indicated that fluoride reduced tooth cavities by approximately 60 percent. These findings prompted policymakers to insist that fluoride be inserted into public water systems. Today, approximately two-thirds of U.S. citizens have fluoride in their drinking water (as do people in Australia, Brazil, Canada, New Zealand, Spain, and the United Kingdom).

But fluoride in the public drinking water has its critics. While some studies that have been brought into question for their methodology have suggested a potential link between fluoride and a number of serious health concerns, other scientists argue that the studies linking fluoride with reduced tooth decay have been poorly designed with weak controls.  In short, the results of several meta-analyses argue there is questionable evidence that fluoride has a significant impact on reducing tooth decay.

In recent years, scientists have turned their attention back to studying potential adverse effects of regular fluoride consumption in the drinking water. Of special interest is the possibility that regular fluoride consumption during pregnancy may adversely affect the unborn child. Some studies have been examining the possibility that increased fluoride consumption during pregnancy may negatively impact intelligence of the offspring.

Study overview

This most recent longitudinal study (published in the American Medical Association’s  JAMA Pediatrics) examined the effects of fluoride on IQ. Psychologists and public health researchers examined a decade of data from Canada’s federally-funded “Maternal-Infant Research on Environmental Chemicals” program–a long-term study of pregnant women and their children in six Canadian cities and chemical exposure. The research program began collecting data in 2008 on myriad of chemicals in food, products and the environment.

Study Methods

The study sample included 601 mother-child pairs recruited from 6 major cities in Canada; children were between ages 3 and 4 years at testing. Data were analyzed between March 2017 and January 2019.

Of 512 mother-child pairs in the final analysis, the mean (SD) age for enrollment for mothers was 32.3 (5.1) years, 463 (90%) were white, and 264 children (52%) were female.

Approximately 41 percent of the women in the study lived in cities with fluoridated drinking water.  Women drinking fluoridated water had an average urinary fluoride level of 0.69 milligrams per liter, compared with 0.4 milligrams for women living in cities without fluoridated water.

Within four years of the women giving birth, researchers administered an age-appropriate IQ test to their children. Children’s IQ was assessed at ages 3 to 4 years using the Wechsler Primary and Preschool Scale of Intelligence-III. Multiple linear regression analyses were used to examine covariate-adjusted associations between each fluoride exposure measure and IQ score.

Findings Overview

In this study, maternal exposure to higher levels of fluoride during pregnancy was associated with lower IQ scores in children aged 3 to 4 years.

After controlling for variables such as parental education level, birth weight, prenatal alcohol consumption, and household income, as well as exposure to environmental toxicants such as lead, mercury, and arsenic, they found that if a mother’s urinary fluoride levels increased by 1 milligram per liter, her son’s IQ score dropped by about 4.5 points.

Secondary testing

The researchers used self-reporting from the mothers as a second method for measuring fluoride intake.  The results of the secondary testing method revealed that a 1-milligram-per-liter increase in fluoride was associated with a 3.7-point IQ score drop in both boys and girls.


Of course many future replication studies are needed before any widespread changes to public policy can be considered. Scientists need to first test and re-test the links between fluoride consumption and IQ with a variety of different populations under a myriad of circumstances.  That said, the researchers of the current study conclude that the findings of their research indicate the possible need to reduce fluoride intake during pregnancy (source).


Journal Reference:  Green, R., et al.  (2019). Association Between Maternal Fluoride Exposure During Pregnancy and IQ Scores in Offspring in Canada, Journal of the American Medical Association’s Pediatrics (JAMA Pediatrics), Study doi:10.1001/jamapediatrics.2019.1729.