A comprehensive analysis of 74 studies from ten countries has found that higher fluoride exposure is associated with lower IQ scores in children, with effects varying based on exposure levels. The research, published in JAMA Pediatrics, evaluated data from more than 20,000 children across multiple continents.
The study comes amid ongoing discussions about fluoride levels in drinking water. In the United States, where no such IQ studies have been conducted, more than 2.9 million residents receive water from systems containing natural fluoride levels above international guidelines.
The research team found that for every 1-milligram per liter increase in urinary fluoride, children’s IQ scores decreased by 1.63 points. This association remained significant even after accounting for study quality and other factors.
Most of the studies examined came from China (45 studies), with others from Canada, Denmark, India, Iran, Mexico, New Zealand, Pakistan, Spain, and Taiwan. The research covered both areas with naturally occurring high fluoride levels and regions with water fluoridation programs.
The findings suggest particular attention should be paid to areas with elevated natural fluoride levels. Currently, the U.S. Environmental Protection Agency sets an enforceable standard of 4.0 mg/L and a recommended standard of 2.0 mg/L for fluoride in drinking water. The World Health Organization’s guideline is 1.5 mg/L.
The study found that adverse associations persisted at levels below 2.0 mg/L when measuring fluoride in urine, which captures total exposure from all sources including water, food, and dental products. However, when looking only at water fluoride levels, the associations became less clear below 1.5 mg/L.
Significant disparities exist in U.S. fluoride exposure, particularly affecting Hispanic and Latino communities. The U.S. Geological Survey estimates that 172,000 Americans use domestic wells exceeding the EPA’s highest standard, while 522,000 use wells above the recommended level.
The CDC currently recommends that parents of children under 8 years old and parents of bottle-fed infants seek alternative water sources if their drinking water contains more than 2 mg/L of fluoride, though these recommendations focus on preventing dental fluorosis rather than cognitive effects.
While the research team emphasized that this analysis wasn’t designed to address broader public health implications of water fluoridation in the United States, they noted that the findings could inform future risk-benefit assessments of fluoride exposure.
The research represents the most comprehensive analysis to date of fluoride’s potential cognitive impacts, though the authors note that more research is needed, particularly at lower exposure levels. No U.S.-based studies were available for inclusion, and nationally representative data on American fluoride exposure levels remains limited.
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