“Taking these many important concerns together, readers are advised to exercise great caution in drawing conclusions about possible associations between fluoride exposure and lower IQ,” Levy concluded. “This is especially true at lower water fluoride levels.”
Another controversial study
But the water fluoridation debate is unlikely to go away anytime soon. In a second editorial published alongside the NTP study, other researchers praised the analysis and called on health organizations and regulators to reassess fluoridation.
“The absence of a statistically significant association between water fluoride less than 1.5 mg/l and children's IQ scores in the dose-response meta-analysis does not dismiss fluoride as a potential risk for lower IQ scores at levels found in fluoridated communities,” The authors argue that there are additional sources of fluoride, such as toothpaste and food.
The EPA estimates that 40 to 70 percent of human fluoride exposure comes from water.
Two of the three authors of the second editorial – Christine Till and Bruce Lanphear – were authors of a highly controversial 2019 study from Canada, which suggested that fluoride intake during pregnancy could lower children's IQ. The authors even suggested that pregnant people should reduce their fluoride intake. But the study, also published in JAMA Pediatrics, only found a link between maternal fluoride levels and IQ in male children. There was no association in women.
The study provoked strong reactions, with blistering responses published in JAMA Pediatrics. In one response, British researchers essentially accused Till and colleagues of conducting a statistical fishing expedition to find a link.
“[T]there was no significant IQ difference between children from fluoridated and non-fluoridated communities and no overall association with maternal urinary fluoride (MUFSG). The authors did not mention this and instead emphasized the significant sexual interaction, with the association appearing for boys but not for girls. No theoretical basis for this test was provided; in the absence of a pre-registration for the study, we cannot know whether this was planned a priori. If not, the false positive rate increases because there are many potential subgroups that could show the result by chance.”
Other researchers criticized the study's statistics, the lack of transparency of the data, the use of maternal urine samples, and the test they used to assess the IQ of children aged 3 and 4.
