By Douglas Main Fluoride exposure is consistently linked with lowered IQ, according to a landmark analysis of more than 70 published studies on the subject. The paper, published January 6 in the journal JAMA Pediatrics and authored by scientists with the National Institutes of Health, found a significant inverse relationship between measures of fluoride exposure and IQ in 64 of 74 studies. The study, the largest meta-analysis of its kind, found that those exposed to high levels of fluoride have measurably lower IQs, equivalent to a difference of nearly 7 IQ points, compared to those in the low fluoride groups. This conclusion came from 59 studies that looked at levels higher than those used in water fluoridation. The study found the link between fluoride and IQ loss persisted even at low levels of fluoride, as measured in human urine samples. The meta-analysis is an offshoot of the National Toxicology Program’s investigation into fluoride’s likely impact on neurodevelopment and cognition, published in August 2024, and comes at a time of heightened scrutiny of, and debate over, the practice of fluoridation of public drinking water. In a seven-year-long court case that wrapped up in September 2024, US District Judge Edward Chen of the Northern District of California, ordered the US Environmental Protection Agency (EPA) to take regulatory action to eliminate the “unreasonable risk” that water fluoridation presents. The fluoridation of water at 0.7 ppm “poses an unreasonable risk of reduced IQ in children,” Chen wrote in his decision. Many researchers are sharply divided over the issue, however.