Does Fluoride Lower IQ?

Published by: International IQ Test
Last updated: November 9, 2026

Introduction

The practice of adding fluoride to drinking water began in the United States in 1945. Today, water fluoridation is used in several countries, including Canada, Chile, Singapore, Hong Kong, Malaysia, Ireland, New Zealand, and Brazil, to help prevent tooth decay.

Fluoride is also added to toothpaste because it helps protect teeth. But is fluoride good for our brains? Several studies have explored this question. Here is what they found.

1. Higher fluoride exposure is associated with lower IQ in children

A study by Taylor et al. (2025), published in JAMA Pediatrics, found a statistically significant association between higher fluoride exposure and lower IQ in children.

The more fluoride children are exposed to, the lower their average IQ tends to be, with a decrease of approximately 1.63 IQ points for every 1 mg/L increase in urinary fluoride concentration, according to Taylor et al. (2025), whose study includes an analysis of 13 studies with individual-level measurements.

A statistically significant association was also observed in some analyses of urinary fluoride concentrations below 1.5 mg/L. However, the association was not statistically significant in the overall analysis of drinking water concentrations below 1.5 mg/L.

The study does not establish the lowest exposure level at which an effect on IQ might occur, or whether a “risk-free range” exists. However, it shows that higher exposure tends to be associated with lower average IQ.

A Harvard meta-analysis reached similar conclusions. In studies primarily examining high fluoride concentrations, children in the higher-exposure groups scored, on average, the equivalent of approximately 7 IQ points lower than those in the lower-exposure groups.

A prospective Canadian study by Green et al. (2019), published in JAMA Pediatrics, also observed an association between fluoride exposure during pregnancy and lower IQ in children. Its analysis of maternal urinary fluoride included 512 mother–child pairs.

In the communities studied, average fluoride concentrations in drinking water were 0.59 mg/L in fluoridated areas, compared with 0.13 mg/L in non-fluoridated areas. In an additional adjusted analysis, each 1 mg/L increase in water fluoride concentration was associated with an average decrease of 5.29 IQ points in children (95% confidence interval: −10.39 to −0.19). This finding comes from a secondary statistical analysis of a subsample and does not represent a directly measured difference in IQ between the two groups. This statistical association does not, however, establish causation.

A study by Grandjean et al. (2023), combining three prospective cohorts from Denmark, Canada, and Mexico, with more than 1,500 mother–child pairs in total, also found a statistically significant association between prenatal fluoride exposure and lower IQ in children.

The researchers estimated an average decrease of 2.06 IQ points for every 1 mg/L increase in maternal urinary fluoride concentration, with a modeled benchmark concentration of 0.45 mg/L and a lower confidence limit of 0.28 mg/L. They concluded that pregnant women and children may need protection against fluoride neurotoxicity. However, when analyzed separately, the Danish cohort showed no significant association, and these concentrations are not established thresholds at which fluoride has been proven to cause toxicity.

2. How excessive fluoride exposure could affect the brain

A 2024 scientific review describes four possible biological mechanisms through which excessive fluoride exposure could affect the body, particularly the brain:

• Oxidative stress: Excessive fluoride exposure can increase the production of reactive oxygen species and disrupt antioxidant defenses in nerve cells.
• Mitochondrial dysfunction: Mitochondria produce ATP, the energy source neurons need to function. In some experimental models, fluoride disrupts mitochondrial function.
• Synaptic disruption: Experiments have shown changes in neuronal signaling and synaptic plasticity, both of which are involved in learning and memory.
• Disrupted cellular calcium regulation: Calcium regulates the transmission of nerve signals. Disruptions in calcium regulation can lead to cellular dysfunction or even neuronal damage.

These mechanisms have primarily been studied in experimental models and do not, on their own, demonstrate the effects of low-dose exposure in humans.

Conclusion

Studies show that greater fluoride exposure in children tends to be associated with lower IQ, particularly at high concentrations. A threshold below which exposure has no effect at all on cognitive development has not been clearly established.

The WHO currently recommends that fluoride concentrations in drinking water should not exceed 1.5 mg/L. However, the Canadian study by Green et al. (2019) also observed an association between higher fluoride exposure and lower IQ in children in communities where average water concentrations ranged from 0.13 to 0.59 mg/L, depending on fluoridation status.

Fluoride exposure remains widespread today, whether through fluoridated water in some countries or through fluoride toothpaste, some of which may be swallowed.

It is therefore relevant to consider total fluoride exposure, particularly during pregnancy and childhood, while keeping in mind that observational studies alone do not establish causation.

Large prospective studies combining repeated measurements of fluoride exposure, brain MRI scans, cognitive tests, and methods that better control for confounding factors would help clarify the biological mechanisms involved and provide a stronger basis for assessing causality.