Another Study Shows Fluoride in the Water Reduces Children’s IQ

Ever since fluoride was first added to drinking water in Grand Rapids, Michigan, on January 26, 1945, it has been controversial. The “fluoride wars” have been raging ever since. There is little doubt that when municipal water authorities put fluoride in the water supply, it helps prevent tooth decay. But how much does it help?

Are there any downsides about fluoride that people should know about? Another new study reveals that children’s IQ may be impacted by early exposure to fluoride in the water they drink (Environmental Health Perspectives, March 5, 2025). This comes shortly after a meta-analysis of previous research raises questions about the safety of water fluoridation (JAMA Pediatrics, Jan. 6, 2025).

The Latest Research on Fluoride in Water:

Several studies have suggested that children exposed to fluoridated drinking water as babies have a modest decline in their IQ. A new study of 500 mothers and their children in Bangladesh confirms that higher levels of fluoride in the water are linked to cognitive difficulties, especially with verbal reasoning and sensory processing.

This fluoride occurs naturally in the Bangladeshi water.  (EHP, March 5, 2025):

“There are indications that fluoride exposure considered to be beneficial for dental health may not be safe from a neurodevelopmental perspective.

The Results of the Study:

“Maternal urinary fluoride in early pregnancy was inversely associated with the children’s cognitive scores both at 5 and 10 years of age, with no apparent threshold below which there appeared to be no effect.”

In Bangladesh, the levels of fluoride associated with cognitive deficits in children are below the safe upper limit established by the European Union and the World Health Organization. The investigators point out that their research is in line with other studies.

It was not just prenatal exposure:

“We also found that the children’s contemporary fluoride exposure was inversely associated with
their cognitive abilities at 10 years of age, although at higher exposure levels. Like with prenatal
fluoride exposure, the association was mainly driven by lower scores of perceptual reasoning and
verbal comprehension.”

According to Dr. Maria Kippler, lead author from the Karolinska Institute in Sweden:

“Our results support the hypothesis that even relatively low concentrations of fluoride can impact children’s early development.”

A Meta-Analysis of Fluoride in Water:

The authors of the study published in JAMA Pediatrics (Jan. 6, 2025) analyzed 74 studies from around the world. All examined the relationship between fluoride exposure and children’s IQ. The investigators reported a dose-response relationship between fluoride in water and urine and children’s IQ. In other words, the higher the dose, the more deficit was seen in IQ. In the best studies, the drop in IQ was small, just over 1 point on average, but across a population that could be important. Are the benefits worth this risk?

Dentists and Public Health Officials Support Fluoride:

Although there have been questions about fluoride’s potential toxicity, most public health officials dismiss them. They consider water fluoridation one of the top ten public health achievements of the last century. However, the level of support is no longer as strong as it once was.

The Cochrane Collaboration is an independent collection of scientists and scholars. Cochrane describes itself this way:

“Cochrane is for anyone interested in using high-quality information to make health decisions. Whether you are a doctor or nurse, patient or carer, researcher or funder, Cochrane evidence provides a powerful tool to enhance your healthcare knowledge and decision making.”

Here is what Cochrane says about fluoride in the water to prevent tooth decay (Cochrane Database of Systematic Reviews, Oct. 4, 2024):

“Contemporary studies indicate that initiation of CWF [community water fluoridation] may lead to a slightly greater reduction in dmft [decayed, missing or filled teeth] and may lead to a slightly greater increase in the proportion of caries‐free children, but with smaller effect sizes than pre‐1975 studies. There is insufficient evidence to determine the effect of cessation of CWF on caries and whether water fluoridation results in a change in disparities in caries according to socioeconomic status. We found no eligible studies that report caries outcomes in adults.

“The implementation or cessation of CWF requires careful consideration of this current evidence, in the broader context of a population’s oral health, diet and consumption of tap water, movement or migration, and the availability and uptake of other caries‐prevention strategies. Acceptability, cost‐effectiveness and feasibility of the implementation and monitoring of a CWF programme should also be taken into account.”

The Flip Side of the Fluoride Debate:

I remember riding in the car with my parents in the 1950s when a radio announcer insisted, with great passion, that fluoridation was a communist plot to make Americans dumber. My parents thought the guy was a total kook. Most Americans agreed.

Over the course of the following decades, water fluoridation became more popular. Two-thirds of U.S. citizens now ingest fluoride in their water. In addition, there is fluoride in toothpaste and mouthwash.

Fluoride and IQ?

An earlier study in JAMA Pediatrics (Oct. 1, 2019) suggested that when pregnant women are exposed to higher levels of fluoride, their infants may have lower IQs as they grow up.

The researchers studied 512 mother-child pairs from six Canadian cities. Roughly 40% of them had fluoride in the water. Urine samples during pregnancy measured the mothers’ fluoride exposure. The investigators also estimated exposure based on the women’s reports of their drinking water sources during pregnancy.

They found that women with the highest levels of fluoride in their urine had sons with modestly lower IQ scores at three to four years of age. When the researchers considered total fluoride exposure of the mothers during pregnancy, both boys and girls were affected.

Other Fluoride Research:

This is not the first study to suggest that fluoride in water might be neurotoxic for developing brains.

In the JAMA Pediatrics article, the authors point out:

“Fluoride crosses the placenta, and laboratory studies show that it accumulates in brain regions involved in learning and memory and alters proteins and neurotransmitters in the central nervous system. Higher fluoride exposure from drinking water has been associated with lower children’s intelligence in a meta-analysis of 27 epidemiologic studies and in studies including biomarkers of fluoride exposure.”

What Conclusions Can We Draw?

The authors offer the following summation of their research:

“In this prospective birth cohort study from 6 cities in Canada, higher levels of fluoride exposure during pregnancy were associated with lower IQ scores in children measured at age 3 to 4 years. These findings were observed at fluoride levels typically found in white North American women. This indicates the possible need to reduce fluoride intake during pregnancy.”

Is Fluoride in Water Worrisome?

This study was only about prenatal fluoride exposure. The results are likely to be divisive. The editors of JAMA Pediatrics acknowledged the sensitivity of the topic.

Here is what they said in justifying publication of this research (JAMA Pediatrics, Oct. 1, 2019):

“This decision to publish this article was not easy. Given the nature of the findings and their potential implications, we subjected it to additional scrutiny for its methods and the presentation of its findings. The mission of the journal is to ensure that child health is optimized by bringing the best available evidence to the fore. Publishing it serves as testament to the fact that JAMA Pediatrics is committed to disseminating the best science based entirely on the rigor of the methods and the soundness of the hypotheses tested, regardless of how contentious the results may be.”

Babies Drinking Tap Water Also Score Lower:

The same group of investigators also analyzed data on tap water consumption (including in baby formula) and IQ among young children (Environment International, Jan. 2020). They collected the information from Canadian cities that either had fluoridated water or did not. Babies drinking formula made with fluoridated water had an 8.8 point lower score on Performance IQ. As the researchers put it, this indicates “diminished non-verbal intellectual abilities.”

What Are Your Thoughts About Fluoride in Water?

We know that this research will be controversial. There is another recent study that adds to concerns about the safety of fluoride in water. Here is a link to fluoride exposure and kidney and liver function in adolescents.

Would you like to listen to different perspectives on fluoride from highly credentialed health authorities? You can hear our recent podcasts at these links:

Show 1417: Examining the Pros and Cons of Water Fluoridation (Part 1)
In this, the first of a two-part series, we consider the benefits of water fluoridation.

Show 1418: More About the Pros and Cons of Water Fluoridation (Part 2)
In this second episode of our two-part series, you will learn about the cons of water fluoridation.

After listening to a balanced discussion you will be better able to make up your mind about the benefits and risks of fluoride. Please share your thoughts in the comment section.

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