Large analysis links high fluoride levels with lower IQs in children
Click Here to Manage Email Alerts
Key takeaways:
- In the United States, the recommended fluoride concentration in drinking water is 0.7 mg/L.
- Researchers found a significant decrease in IQ scores among children exposed to fluoride levels at more than twice that amount.
A systematic review and meta-analysis of dozens of studies showed a link between exposure to high levels of fluoride and lower IQ scores in children, according to findings published Monday in JAMA Pediatrics.
None of the studies included in the analysis were conducted in the United States, and the level of fluoridation found to be associated with lower IQs was more than double the level recommended for the U.S. drinking supply.
Initial findings from the project were published in August by the National Toxicology Program, which reported then that “there were insufficient data to determine if the low fluoride level of 0.7 mg/L” — the concentration recommended for drinking water by the U.S. Public Health Service — “has a negative effect on children’s IQ.”
Previous studies have shown that prenatal fluoride exposure is associated with lower IQ scores in preschoolers and a higher risk for neurobehavioral issues among toddlers. Additionally, researchers have reported a link between chronic low-level fluoride exposure and reduced kidney and liver function among adolescents.
The U.S. government has recommended adding fluoride to drinking water since 1962 to reduce cavities and protect oral health. Water fluoridation in the U.S. has received renewed attention since President-elect Donald J. Trump’s nominee for HHS secretary, Robert F. Kennedy Jr., recommended ending the intervention.
Study findings
In the newly published study, Kyla W. Taylor, PhD, a health scientist in the division of translational toxicology at the NIH, and colleagues noted that the CDC “estimates that water and processed beverages (eg, soda and juices) provide approximately 75% of a person’s fluoride intake” and that the Environmental Protection Agency “estimates that 40% to 70% of a person’s fluoride intake comes from fluoridated drinking water.”
“Accumulating evidence suggests that fluoride exposure may affect brain development,” they wrote.
They performed a meta-analysis of 74 studies from 10 countries to assess associations between fluoride consumption and IQ in children. Most of the studies were cross-sectional (64), whereas 10 were prospective cohort studies. More than half (45) were from China. Twelve were from India, and the rest were from Canada, Denmark, Iran, Mexico, New Zealand, Pakistan, Spain and Taiwan.
The researchers reported that 52 studies had a high risk of bias and 22 had a low risk of bias.
In an analysis of 59 studies with 20,932 children, the researchers found that children who had higher exposures to fluoride had lower IQ scores compared with those who had lower fluoride exposure (random-effects pooled standardized mean differences [SMD] = –0.45; 95% CI, –0.57 to –0.33).
The association was stronger among 47 studies with a high risk of bias (SMD = –0.52; 95% CI, –0.68 to –0.37), but still statistically significant among 12 studies with low risk of bias (SMD = –0.19; 95% CI, –0.35 to –0.4), Taylor and colleagues reported.
The researchers reported an inverse linear relationship between IQ scores and fluoride levels in drinking water (SMD = –0.15; 95% CI, –2 to –11) or urine (SMD = –0.15; (95% CI, –0.23 to –0.07). The association was still statistically significant for urine levels below 1.5 mg/L and drinking water levels below 2 mg/L but not lower than 1.5 mg/L.
Data from 13 studies that included 4,475 children showed that every 1 mg/L more fluoride in children’s urine was associated with a 1.63-point lower IQ score (95% CI, –2.33 to –0.93). When the researchers narrowed the results to 11 studies with a low risk of bias, they found that 1 mg/L more urinary fluoride was linked to a 1.14-point decrease in IQ (95% CI, –1.68 to –0.61).
‘No evidence’ of adverse effect at US concentrations
Although there was not a statistically significant decrease in IQ scores in communities with fluoride levels below 1.5 mg/L in drinking water, the study “does not exonerate fluoride as a potential risk for lower IQ scores at levels found in fluoridated communities,” Bruce P. Lanphear, MD, MPH, a professor of health sciences at Simon Fraser University in Vancouver, Canada, and colleagues wrote in a related editorial. “Water fluoride concentration does not capture the amount of water ingested or other sources of ingested fluoride.”
Taylor and colleagues noted that, globally, WHO recommends a maximum of 1.5 mg/L in drinking water.
Lanphear and colleagues argued that the results of the study align with concerns about vulnerable groups like children in low-income households, pregnant women, infants and those who live in fluoridated communities.
“It is time for health organizations and regulatory bodies to reassess the risks and benefits of fluoride, particularly for pregnant women and infants,” they wrote.
In another editorial, Steven M. Levy, DDS, MPH, Wright-Bush-Shreves Endowed Professor of Research at the University of Iowa College of Dentistry and Dental Clinics, wrote that readers should be cautious about using the data for public policy decisions.
He pointed out that most of the studies had a high risk of bias, and those with lower risk of bias had highly diverse results.
He also noted that the recommended fluoride level for communities in the U.S. is 0.7 mg/L, and said an “optimally fluoridated community” would have fluoride concentrations of around 0.5 mg/L. “However, Taylor and colleagues use a difference of 1.0 mg/L in their calculations, artificially doubling the estimated impact on IQ,” Levy wrote.
“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 community water fluoridation systems,” he wrote. “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, and the widespread use of fluoride for caries prevention should continue.”
References:
- CDC. Timeline for community water fluoridation. https://www.cdc.gov/fluoridation/timeline-for-community-water-fluoridation/index.html. Accessed Jan. 6, 2024.
- Lanphear BP, et al. JAMA Pediatr. 2025;doi:10.1001/jamapediatrics.2024.5549.
- Levy SM. JAMA Pediatr. 2025;doi:10.1001/jamapediatrics.2024.5539.
- National Toxicology Program. Fluoride exposure: neurodevelopmental and cognition. https://ntp.niehs.nih.gov/whatwestudy/assessments/noncancer/completed/fluoride. Published Aug. 21, 2024. Accessed Jan. 6, 2024.
- Taylor KW, et al. JAMA Pediatr. 2025;doi:10.1001/jamapediatrics.2024.5542.
Perspective
Back to Top
This study is the most comprehensive and up to date to include rigorously conducted meta-analyses examining associations of early life fluoride exposure with child IQ. It observed consistent inverse associations between fluoride exposure and children’s IQ across 64 studies regardless of the measure of exposure or cognitive assessment, study design or geographic location.
The findings show that even urinary fluoride concentrations below 1.5 mg/L are consistently inversely associated with child IQ when considering all studies or only those deemed to be at low risk of bias. Moreover, the findings show that a dose-response relationship between higher fluoride exposure and lower child IQ exists. However, associations between drinking water fluoride alone and child IQ at fluoride concentrations below 1.5 mg/L were less clear. Although effect sizes are smaller on average than those that have been observed in specific studies conducted in North America, a decrement of approximately 1.6 IQ points per 1 mg/L increase in water fluoride can have negative implications for intellectual functioning at the population level, particularly for the extremes of intellectual functioning. The findings suggest that fluoride intake among pregnant women and infants should be reduced.
A notable limitation, however, is that there are no U.S.-based studies included in the meta-analysis given that no U.S.-based studies on fluoride and IQ have been published. Still, the meta-analysis included studies based in Canada and Mexico, for which pregnant women had comparable urinary fluoride levels to pregnant women residing in the U.S. More U.S.-based studies on prenatal, infant and child fluoride exposures in relation to neurocognitive functioning are urgently needed.
Collapse
Taylor KW, et al. JAMA Pediatr. 2025;doi:10.1001/jamapediatrics.2024.5542.
Read more about
Click Here to Manage Email Alerts