Fluoride May Be Linked to Decreased IQ, Says “Limited Data,” Hard-to-Interpret Study

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Fluoride exposure appears to slightly decrease IQ scores in children, a new federal meta-analysis has concluded — but not at the low levels recommended for U.S. drinking water.

Fluoride in drinking water was associated with reduced IQ scores at levels of less than 4 milligrams per liter, but not at less than 1.5 mg/L, according to the analysis by researchers at the National Institute of Environmental Health Sciences.

The recommended level of fluoride in U.S. drinking water is 0.7 mg/L, the U.S. Public Health Service says.

“There were limited data and uncertainty in the dose-response association between fluoride exposure and children’s IQ when fluoride exposure was estimated by drinking water alone at concentrations less than 1.5 mg/L,” concluded the research team led by Kyla Taylor, a health scientist with the NIEHS’ Division of Translational Toxicology.

Researchers found a 1.14-point decrease in IQ score for every 1 mg/L increase in fluoride found in urine, when restricting their analysis to the 11 most trustworthy studies included in the evidence review.

The new evidence review appears in the prestigious journal JAMA Pediatrics, and comes at a time when fluoridation is taking political heat. Robert F. Kennedy Jr., the nominee to lead the Department of Health and Human Services, is an outspoken critic of fluoridation.

Fluoride is added to drinking water to protect against tooth decay, a practice supported by groups like the American Dental Association.

Critics of the new review noted that none of the 74 studies included in the review took place in the United States. Most were conducted in China (45), with others taking place in India (12), Mexico (4), Iran (4), Canada (3) and Pakistan (2).

“The public needs to understand that the levels examined in (the) report are from countries with high levels of naturally occurring fluoride that is more than double the amount recommended by the U.S. Public Health Service to optimally fluoridate community water systems and help prevent dental disease,” Dr. Brett Kessler, president of the American Dental Association, said in a news release.

For the study, the federal researchers sorted available studies on fluoridation based on their risk of bias. Of the studies, 52 were rated high risk of bias and 22 low risk of bias.

In 31 studies looking at fluoride in drinking water, exposure appeared to lower IQ at levels less than 4 mg/L and less than 2 mg/L, but not less than 1.5 mg/L.

Another 20 studies that measured fluoride levels in urine found lowered IQ at less than 4 mg/L, less than 2 mg/L, and less than 1.5 mg/L, researchers said.

The research team noted that the U.S. Environmental Protection Agency (EPA) can take action against a public water source if fluoride levels reach 4 mg/L, and can issue warnings at 2 mg/L.

“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 US population,” the NIEHS team concluded in its paper.

“Although this meta-analysis was not designed to address the broader public health implications of water fluoridation in the United States, these results may inform future public health risk-benefit assessments of fluoride,” the team added.

In an accompanying editorial in JAMA Pediatrics, public health dentist Dr. Steven Levy criticized the evidence review and urged caution in interpreting its findings – particularly when it came to findings based on fluoride found in urine.

“There is scientific consensus that the urinary sample collection approaches used in almost all included studies (ie, spot urinary fluoride or a few 24-hour samples, many not adjusted for dilution) are not valid measures of individuals’ long-term fluoride exposure, since fluoride has a short half-life and there is substantial variation within days and from day to day,” wrote Levy, a professor of research at the University of Iowa College of Dentistry and Dental Clinics.

JAMA Pediatrics also ran a second editorial praising the evidence review.

“What this meta-analysis does is it has a way of synthesizing all of that information, not letting one study drive or five studies drive the results,” editorial co-author Bruce Lanphear, a professor of health sciences at Simon Fraser University, told STAT.

The study shows “not definitive, but sufficient” evidence of fluoride as a neurotoxicant to warrant “an urgent response by federal agencies like the EPA that regulates the amount of fluoride in water,” added Lanphear, who has also served as an expert witness in a lawsuit against the EPA regarding fluoridation. 

The American Dental Association continued to stand by its support for fluoride in a statement responding to the federal report.

“To prevent dental disease the ADA continues to recommend drinking optimally fluoridated water along with twice daily brushing with fluoride toothpaste and eating a healthy diet, low in added sugars,” Kessler said in the statement.

More information

Johns Hopkins University has more about fluoride and dental health.

SOURCE: JAMA Pediatrics, Jan. 6, 2024; American Dental Association statement, Jan. 6, 2024

Source: HealthDay

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