Analysis links fluoride exposure to low IQ but finds 'high risk of bias' in most studies

An analysis of more than 70 studies on fluoride and IQ levels concluded there was a relationship between higher levels of the common water additive and lower IQ levels in children, though a large percentage of the studies were noted as having a "high risk of bias."

The meta-analysis published in the medical journal JAMA Pediatrics was supported by and conducted on behalf of the National Institute of Environmental Health Sciences under the National Institutes of Health.

Assessors looked at 74 studies sourced internationally for the analysis. Studies from China accounted for the majority of those reviewed at 45 studies, or 61 percent. India was the second most represented country in the analysis with 12 studies included.

The studies were also evaluated for bias, and 52 out of the 74 studies, or 70 percent, were found to have a "high risk of bias."

Without excluding any of the studies, the authors concluded that their review found an inverse relationship between higher levels of fluoride in drinking water and urine and children’s IQ. The analysis found that children exposed to higher levels of fluoride had "statistically significantly" lower IQ scores.

When only the 22 studies with low risk of bias were analyzed, the inverse association between fluoride exposure and IQ levels remained the same in studies that looked at fluoride in drinking water at levels of less than 4 mg/L, less than 2 mg/L and less than 1.5 mg/L.

The inverse association between fluoride levels and IQ levels remained the same when the analysis accounted for age, sex, country and exposure timing. The assessors also noted that there are no known epidemiological studies on fluoride exposure and children’s IQ in the U.S., making the results of their analysis difficult to apply to the U.S. population.

They also noted there was "limited data and uncertainty" regarding the effect of fluoride on children's IQ levels when fluoride from drinking water was less than 1.5 mg/L.

The US Public Health Service recommends a fluoride concentration of 0.7 mg/L, which public water systems across the country abide by.

Robert F. Kennedy Jr., President-elect Trump's nominee for secretary of Health and Human Services, is vehemently opposed to water fluoridation and has stated one of his goals if confirmed would be to remove the additive from the U.S. water supply. Water fluoridation is a state and local decision, but theoretical avenues for banning the practice at the federal level do exist.

The National Toxicology Program (NTP) under the Department of Health and Human Services released the findings of its own evaluation of fluoride’s impact on neurodevelopment and cognition in 2024. The NTP concluded that “higher levels of fluoride exposure, such as drinking water containing more than 1.5 milligrams of fluoride per liter, are associated with lower IQ in children.”

However, the office noted there wasn't enough data to determine if the 0.7 mg/L concentration of fluoride used throughout the U.S. similarly has a negative impact on children's IQs.

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