Excess Fluoride Exposure Associated with Lower IQ in Children

New landmark meta-analysis indicates the need to halt artificial water fluoridation using industrial byproducts.

by Nicolas Hulscher, MPH

The study titled, Fluoride Exposure and Children’s IQ Scores: A Systematic Review and Meta-Analysis, was just published in JAMA Pediatrics:

Key Points

Question - Is fluoride exposure associated with children’s IQ scores?

Findings - Despite differences in exposure and outcome measures and risk of bias across studies, and when using group-level and individual-level exposure estimates, this systematic review and meta-analysis of 74 cross-sectional and prospective cohort studies found significant inverse associations between fluoride exposure and children’s IQ scores. For fluoride measured in water, associations remained inverse when exposed groups were restricted to less than 4 mg/L or less than 2 mg/L but not when restricted to less than 1.5 mg/L; for fluoride measured in urine, associations remained inverse at less than 4 mg/L, less than 2 mg/L, and less than 1.5 mg/L; and among the subset of low risk-of-bias studies, there were inverse associations when exposed groups were restricted to less than 4 mg/L, less than 2 mg/L, and less than 1.5 mg/L for analyses of fluoride measured both in water and in urine.

Meaning - This comprehensive meta-analysis may inform future risk-benefit assessments of the use of fluoride in children’s oral health.

In simple terms, here’s what the study found:

1. Higher Fluoride Exposure Linked to Lower IQ Scores:

   • Children exposed to higher levels of fluoride consistently scored lower on IQ tests compared to those with lower exposure.

   • Estimated Impact: On average, children's IQ scores were lower by an SMD of −0.45 (~7 IQ points).

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2. Fluoride in Drinking Water and IQ Scores:

   • When fluoride levels in drinking water increased, children’s IQ scores tended to decrease.

   • At Levels Below 4 mg/L: IQ scores were lower (SMD: −0.22, ~3 IQ points).

   • At Levels Below 2 mg/L: The effect was smaller and less certain (SMD: −0.18, ~3 IQ points).

   • At Levels Below 1.5 mg/L: No clear relationship was detected.

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3. Fluoride in Urine and IQ Scores:

   • Fluoride measured in children’s urine showed a clearer link to lower IQ scores than drinking water fluoride levels.

   • At All Levels of Exposure: Higher urinary fluoride was linked to lower IQ scores (SMD: −0.15, ~2 IQ points).

   • At Levels Below 4 mg/L: The effect remained significant (SMD: −0.20, ~3 IQ points).

   • At Levels Below 2 mg/L: The link persisted (SMD: −0.08, ~1 IQ point).

   • At Levels Below 1.5 mg/L: The link persisted (SMD: −0.08, ~1 IQ point).

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4. Impact of a 1-mg/L Increase in Urinary Fluoride on IQ:

   • For every 1-mg/L increase in fluoride in a child’s urine, their IQ score decreased by about 1.63 points.

   • In the most reliable studies, the decrease was slightly smaller at 1.14 points per 1-mg/L increase.

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A few months ago, I summarized the deleterious effects of excess fluoride consumption and recommended policy that would enforce physical removal of unsafe levels:

Fluoride is not considered an essential nutrient for any biological function in humans or animals. Approximately 72.3% of the U.S. population on community water systems receives fluoridated water. The CDC currently recommends a fluoride concentration in drinking water of 0.7 mg/L to prevent cavities, with a secondary safety standard of 2.0 mg/L. Physical intervention to remove fluoride from water is currently only required when fluoride concentrations exceed the EPA maximum contaminant level (MCL) of 4.0 mg/L. Boehmer et al found that between 2016 and 2021, approximately 83.7% of the time, people served by fluoridated water systems received water with fluoride levels between 0.6 mg/L and 2.0 mg/L. This implies that a significant number of Americans likely receive fluoride levels above 1.5 mg/L, which is the World Health Organization’s safe limit for fluoride. In Europe, only Ireland, Poland, Serbia, Spain, and the UK fluoridate their water. Most developed countries do not consume artificially fluoridated water.

The U.S. uses fluoride derived from industrial byproducts for water fluoridation: “Three chemicals are used to fluoridate drinking water in the U.S: sodium fluoride (NaF); sodium fluorosilicate (Na2SiF6); and fluorosilicic acid (H2SiF6). Fluorosilicic acid is a byproduct of the manufacture of phosphate fertilizer. It is recovered as a vapor, which ensures a high degree of purity. Both sodium fluoride and sodium fluorosilicate are made from fluorosilicic acid recovered in this manner. Sodium fluorosilicate is created by neutralizing fluorosilicic acid with caustic soda, itself a water treatment chemical. Sodium fluoride is created by neutralizing fluorosilicic acid with sodium chloride, common salt.”

Various deleterious health outcomes can occur if water fluoride concentration is above 1.5 mg/L (within the CDC’s safety standard). Kumar et al summarized the major adverse health effects on human beings due to the ingestion of excess fluoride through drinking water (above 1.5 mg/L):

The narrow range between fluoride concentrations that provide purported benefits (0.7 mg/L) and those that pose risks (>1.5 mg/L) presents concerns, especially if fluctuations in concentration occur.

Fluoride is naturally present in the environment and most natural water sources, including bottled waters, and thus can’t be completely removed from the water supply. Some bottled water manufacturers artificially add fluoride to their water or source their water from fluoridated public water systems. Approximately 42% of American children are drinking bottled waters. Johnson and DeBiase found that 95% of the bottled water analyzed (n=65) did not label fluoride content. If there is meaningful public health policy on fluoride, the bottled water industry will have to be properly managed with respect to accurate fluoride testing and labelling.

Since it’s impossible to completely remove fluoride from the environment, gathering precise data on the number of Americans exposed to fluoride concentrations above 1.5 mg/L should be a first priority to identify and protect high-risk populations. Another key policy should be reducing the EPA maximum contaminant level (MCL) for fluoride in public drinking water systems from 4 mg/L to <0.7 mg/L, which would effectively enforce physical intervention to remove unsafe levels of fluoride and discourage artificial supplementation. In avoiding autocracy, this approach could be a first step in collaboration with multiple stakeholders that may disagree with a complete water fluoridation ban, even if it’s indicated. Lastly, we should keep in mind that fluoride is only one element among the sea of other water treatment additives and contaminants that present similar, if not worse, negative health outcomes. To drive meaningful improvements in population health, we need a broader perspective on water and public health safety. Additionally, efforts to enhance water safety should encompass both tap and bottled water.

The most effective action would be to completely halt the artificial introduction of industrial byproduct fluoride into the water supply, which would likely lead to the recovery of the IQ of American children and prevent other adverse health outcomes associated with excess fluoride exposure.

Nicolas Hulscher, MPH

Epidemiologist and Foundation Administrator, McCullough Foundation

www.mcculloughfnd.org

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