High Fluoride Exposure Linked to Lower IQ in Kids

Higher fluoride exposure was linked to lower IQ among children, a large meta-analysis indicated, although with limited data quality.

Inverse associations and a dose-response association were found between fluoride measurements in urine and drinking water and children’s IQ across literature from multiple countries, reported Kyla Taylor, PhD, of the National Institute of Environmental Health Sciences in Morrisville, North Carolina, and colleagues.

Among 20,932 children across 59 studies with group-level measures of fluoride in drinking water, dental fluorosis, or other measures of fluoride exposure, there was an inverse association between fluoride exposure and IQ. The pooled standardized mean difference (SMD) of −0.45 (95% CI −0.57 to −0.33, P

However, there were limited data and uncertainty in the dose-response association between fluoride exposure and children’s IQ when fluoride exposure was estimated by drinking water alone at concentrations less than 1.5 mg/L, they noted in JAMA Pediatrics.

“Fluoridated water has been used for decades to reduce dental cavities and improve general oral health,” Taylor wrote in emailed remarks. “However, there is concern that pregnant women and children are getting fluoride from many sources including drinking water, water-added foods and beverages, teas, toothpaste, floss, and mouthwash, and that their total fluoride exposure is too high and may affect fetal, infant, and child neurodevelopment.”

The WHO-defined upper safe limit of fluoride in drinking water is 1.5 mg/L, while the Environmental Protection Agency (EPA) allows up to 4 mg/L, and the U.S. Public Health Service recommends a fluoride concentration of 0.7 mg/L. But “levels above 1.5 mg/L are found in wells and community water systems that serve over 2.9 million people in the United States,” Taylor noted. The meta-analysis lacked sufficient data to evaluate whether 0.7 mg/L of fluoride exposure in drinking water affected children’s IQ, she said.

Opinions were split on the implications of the findings.

“It is time for health organizations and regulatory bodies to reassess the risks and benefits of fluoride, particularly for pregnant women and infants,” Bruce Lanphear, MD, MPH, of Simon Fraser University in Vancouver, and colleagues concluded in one editorial accompanying the study in JAMA Pediatrics.

A second editorial by Steven Levy, DDS, MPH, of the University of Iowa in Iowa City, argued that “despite the presentation of some evidence of a possible association between IQ and high fluoride levels in water, there is no evidence of an adverse effect at the lower water fluoride levels commonly used in CWF [community water fluoridation] systems.”

“Therefore, public policy concerning the addition of fluoride to community water systems and recommendations concerning the use of topical fluoride in its many forms should not be affected by the study findings,” Levy contended, “and the widespread use of fluoride for caries prevention should continue.”

Fluoridation of water in communities across the country has come into focus with a recent federal judge’s decision that ordered U.S. regulators to consider the risk that fluoride in water could cause lower IQ in kids and with discussion of changes being pushed by the incoming Trump administration.

The studies examined by Taylor and colleagues consisted of 64 cross-sectional studies and 10 cohort studies. Most (45) were conducted in China, with other locations including Canada, Denmark, India, Iran, Mexico, New Zealand, Pakistan, Spain, and Taiwan. Notably, 52 of the studies were rated as having a high risk of bias.

In the meta-analysis, 64 studies indicated inverse associations between fluoride exposure measures and children’s IQ. When restricting the analysis to the 12 studies with low risk of bias, the SMD dropped to −0.19 (95% CI −0.35 to −0.04) between high and low exposed groups, equivalent to a 2.8-IQ point decrement.

And among 31 studies with fluoride measured in drinking water, there was a dose-response association between exposed and reference groups (SMD −0.15, 95% CI −0.20 to −0.11, P

Though associations remained inverse when exposed groups were restricted to less than 4 mg/L and less than 2 mg/L of fluoride in drinking water, the association was null at less than 1.5 mg/L. In analyses restricted to studies with low risk of bias, the association remained inverse when exposure was restricted to less than 4 mg/L, less than 2 mg/L, and less than 1.5 mg/L, although losing statistical significance.

Additionally, among 20 studies with fluoride measured in urine, there was an inverse dose-response association (SMD −0.15, 95% CI −0.23 to −0.07, P

Associations remained inverse when exposed groups were restricted to less than 4 mg/L, less than 2 mg/L, and less than 1.5 mg/L of fluoride in urine.

Among 13 studies with individual-level measures, there was an IQ score decrease of 1.63 points (95% CI −2.33 to −0.93, P

Ultimately, the current work “may inform future risk-benefit assessments of the use of fluoride in community drinking water and children’s oral health products,” Taylor said.

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