A new meta-analysis published in JAMA Pediatrics is reigniting the long-standing debate surrounding water fluoridation, a public health practice hailed for its role in preventing tooth decay. The study, which derives data from dozens of international research papers, suggests a potential link between higher fluoride exposure in children and lower IQ scores. The authors acknowledge limitations and stress that the analysis doesn’t address the broader public health implications of water fluoridation in the United States. By releasing it, they will further fuel the politicized controversy surrounding this widespread practice.
The meta-analysis, stemming from a larger effort by the National Toxicology Program (NTP) to assess the evidence on the connection between fluoride and IQ, analyzed data from 74 studies. The findings indicated that, overall, increased fluoride exposure was associated with a slight decrease in children’s IQ scores. However, researchers deemed many of the studies included in the analysis to have a “high risk of bias.” Also, researchers worry that this bias results because none of the included studies were conducted within the United States.
A Contentious History of Water Fluoridation
For nearly 80 years, communities in the U.S. have been adding fluoride to tap water, as a measure to combat tooth decay. This practice has been credited with reducing cavities by approximately 25%, according to the Centers for Disease Control and Prevention (CDC). However, opposition to water fluoridation has persisted, ranging from evidence-based concerns to unsubstantiated claims and conspiracy theories. This opposition has gained renewed attention with President-elect Donald Trump’s head of the Department of Health and Human Services, Robert F. Kennedy Jr., a vocal critic of fluoridation and an anti-vaccine activist, could significantly influence policy on the matter if confirmed.
Examining the New Meta-Analysis
The JAMA Pediatrics study delves into the data behind a 324-page monograph on fluoride released by the NTP last August. The recent meta-analysis combined data from 74 studies primarily conducted in China and India, with the bulk of the studies (approx. 45 studies) coming from China and 12 from India. Researchers did not review any persons from the U.S. in the studies, although they reviewed 3 from Canada and 4 from Mexico.
The meta-analysis explored the relationship between fluoride levels and children’s IQ. That report concluded with “moderate confidence” that a link may exist between high fluoride exposure and lowered IQ. This potential association suggests possible harm to brain development in pregnant individuals or young children exposed to drinking water containing at least 1.5 milligrams of fluoride per liter (mg/L), a concentration exceeding twice the recommended level of 0.7 mg/L in the U.S. water supply. Christine Flowers, Director of the Office of Communication at the National Institutes of Health (NIH), make clear that the available data was not enough to determine whether fluoride exposure at the U.S. recommended level of 0.7 mg/L affected children’s IQ.
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Differing Perspectives on the Study
The publication of the meta-analysis was accompanied by two opposing editorials in JAMA Pediatrics, reflecting the divergent opinions on the matter. Steven Levy, a public health dentist at the University of Iowa, penned one editorial questioning the analysis’s methods and disagreeing with its conclusions. The other editorial, authored by a trio of children’s health researchers, supported the study’s findings..
Levy contends that the science underpinning the analysis is not as strong as presented by the authors. For instance, while the study’s abstract suggests a link between fluoride exposure and lower IQ even below 1.5 mg/L, Levy argues that the data provided are inconclusive. He also points out the study’s failure to fully consider recent research that challenges the association between fluoride exposure and IQ. Levy highlights a pattern in public health research where initial studies suggest a problem, but as the issue is studied more thoroughly, “the evidence goes in a somewhat different direction.” He emphasizes that researchers should have prioritized more recent, well-designed fluoride studies, as these have found no negative effect on IQ.
Fluoride and IQ
Conversely, Dr. Bruce Lanphear, a children’s health researcher at Simon Fraser University and co-author of the editorial supporting the paper’s findings, believes that the analysis, despite imperfect evidence, presents a strong enough case for action. He argues that “what the study does, or should do, is shift the burden of proof,” placing the responsibility on advocates of fluoridation to prove its safety.
Lanphear shares concerns that the base level of fluoridation, compounded by numerous other sources of fluoride, such as toothpaste, mouthwash, and certain foods and drinks, could be pushing fluoride levels to harmful levels in vulnerable individuals. Flowers of the NIH echoed this concern, stating that “there is concern that pregnant women and children are getting fluoride from many sources … and that their total fluoride exposure is too high and may affect infant and child brain development”.
Fluoride: Beneficial or problematic?
While water fluoridation undeniably prevents cavities, Lanphear contends that its relative benefits have dropped in recent decades due to the widespread use of fluoridated toothpaste, a point backed up by a recent analysis by U.K. researchers. He suggests exploring alternative methods to protect children from developing cavities, such as maintaining the consumption of sugary drinks or implementing education programs to improve children’s understanding of dental health and practices. Lanphear advocates for a reassessment of the potential risks of fluoride against its benefits.
Levy, however, emphasizes the important and understated benefits of water fluoridation. He notes that “it isn’t that cavities are under control for everyone,” and fluoridated water particularly benefits those who are poor and who may lack access to fluoridated toothpaste or regular dental care. He also argues that alternative methods of cavity prevention are far more costly. Levy asserts that “even [providing] fluoride toothpaste for individuals would be 10 to 20 times more costly than water fluoridation. Using fluoride mouth rinses or going to the dentist to get fluoride treatments would be much more expensive”.
Methodological Concerns and Transparency
Critics of the meta-analysis, including Dr. Steven Levy, have raised concerns about its methodology and lack of transparency. Levy notes that only 12 of the 59 studies central to the analysis had a low risk of bias, and eight of those found no inverse connection between fluoride and IQ.
Dr. Levy also criticizes the use of urine to measure fluoride exposure, arguing that it contradicts the “scientific consensus”. This is because urinary fluoride measurements vary significantly and may not accurately reflect long-term exposure. He further accuses the report authors of cherry-picking studies, pointing to the leaving out of a publication based on data from the Canadian Maternal-Infant Research on Environmental Chemicals study, which found no link between fluoride exposure and IQ.
Moreover, Levy highlights the “lack of transparency” surrounding the report’s connection to the controversial monograph produced for the NTP. He notes that the initial drafts of the monograph received harsh peer reviews. Reviewers have found a lack of clear evidence supporting the claim that “fluoride is presumed to be a cognitive development hazard to humans”. Levy also points out that animal studies using fluoride levels reflecting the U.S. standard of 0.7 mg/L found “no exposure-related differences in motor, sensory, or learning and memory performance”.
Fluoride Exposure Levels and Sources
In the U.S., the EPA sets a maximum concentration of 4 mg/L for fluoride in drinking water. The Public Health Service recommends an optimal concentration of 0.7 mg/L. Various methods can measure fluoride exposure, including assessing fluoride levels in drinking water and urine, as well as examining dental fluorosis, a condition caused by excessive fluoride intake. Exposure can also occur through environmental factors like pollution from burning coal with high fluoride content. It’s important to note that approximately 63% of Americans receive fluoridated water, including 3.5% with fluoride levels exceeding optimal levels, according to the CDC.
Implications and Future Directions
The authors of the JAMA Pediatrics meta-analysis acknowledged that their work was not designed to address the broader public health implications of water fluoridation in the United States. However, they suggested that their findings “may inform future public health risk-benefit assessments of fluoride”. A second editorial accompanying the report argued that it raises enough questions to warrant a reassessment of “the potential risks of fluoride during early brain development”. It further stated that the lack of a clear link between IQ scores and fluoride exposure below 1.5 mg/L “does not exonerate fluoride as a potential risk”. Despite these concerns, Levy maintains that “there is no evidence of an adverse effect at the lower water fluoride levels commonly used” in water systems in the U.S. He concludes that “the widespread use of fluoride for [cavity] prevention should continue”.
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