The nation’s efforts to supplement our drinking water with fluoride has faced (sometimes fervent) opposition since its launch back in the 1940s.
Even today, Robert F. Kennedy Jr., the latest nominee for Secretary of Health Human Services, insisted recently on social media that he would end the practice, calling it “an industrial waste associated with arthritis, bone fractures, bone cancer, IQ loss, neurodevelopmental disorders, and thyroid disease.”
It’s in the shadow of this renewed controversy that researchers have published the results of a four-year review and meta-analysis that uncovered a statistically significant inverse connection between fluoride exposure and kids’ IQ.
The exhaustive research project, which pulled data from more than six dozen publications worldwide, offers fresh insight into potential links between fluoride exposure and neurodevelopmental challenges.
Critical Findings
The analysis, appearing in JAMA Pediatrics, covered 64 cross-sectional and 10 prospective cohort studies. Most of them – 64 – reported the inverse relationship between fluoride exposure and children’s IQ scores.
Working from individual- and group-level data, the study’s authors gauged exposure by measuring (community) water fluoride levels and (individual) urinary fluoride concentrations. Simply put, the researchers found that:
- Children exposed to higher fluoride levels boasted lower IQ scores compared to those with lower exposure levels.
- Higher fluoride levels corresponded with greater IQ reductions. The relationship persisted at fluoride concentrations below 4 milligrams per liter (mg/L) and 2 mg/L. But the effect faded at lower levels, below 1.5 mg/L.
- A 1 mg/L increase in urinary fluoride caused a 1.63-point decrease in IQ. However, the effect appeared slightly less pronounced – 1.14 points – in studies with a lower bias risk.
These results, however, come tied to a few notable caveats. For starters, most the studies emerged from countries – such as China – that integrate much higher fluoride levels into their drinking water. In fact, the review didn’t include any research from the United States, which incorporates much lower fluoride levels.
“To our knowledge, no studies of fluoride exposure and children’s IQ have been performed in the United States, and no nationally representative urinary fluoride levels are available, hindering application of these findings to the U.S. population,” the researchers wrote.
Also, the paper’s authors stopped short of suggesting a direct cause and effect. Instead, they suggested a potential link. Part of that stems from the fact that most of the research failed to account for other factors, such as socioeconomic conditions and other environmental toxins.
The authors added that “Fifty-two studies were rated high risk of bias, and 22 were rated low risk of bias.”
Debating the Implications
Nevertheless, the paper argues that these potential neurodevelopmental risks raise significant public health concerns.
The authors add that these results align with earlier data that suggests that fluoride exposure, particularly during critical periods of brain development, might adversely affect intelligence.
The University of Iowa’s Steven M. Levy, DDS, MPH, however, urged restraint in how we interpret these results. In an editorial – appearing in the same issue of JAMA Pediatrics – Levy raised questions about the bias levels in the research used.
“Taylor et al do not adequately justify selection or omission of studies or explain or justify the calculated individual effect sizes presented in the main analysis,” he wrote. “Also, readers are not told which studies with lower risk of bias are included in the sub analyses for water fluoride levels less than 1.5 mg/L, less than 2.0 mg/L, and less than 4.0 mg/L; therefore, readers cannot independently consider important differences across these studies.”
Further Reading
Cognition in Schizophrenia: A Systematic Review of Wechsler Adult Intelligence Scale Studies
