Divisive review asserts link between fluoride levels, IQ loss

Fluoride, which also occurs naturally in varying levels, helps restore minerals lost to acid breakdown in teeth.

Published in the Journal of the American Medical Association (JAMA) Pediatrics it has sparked pushback from some scientists who criticise the study’s methods, defend the mineral’s proven dental benefits, and warn the findings may not directly apply to typical water fluoridation levels.

Its release comes as US President-elect Donald Trump prepares to take office. His health secretary nominee, Robert F. Kennedy Jr., is a vocal critic of fluoridated water, which currently serves nearly two-thirds of the US population.

Researchers from the National Institute of Environmental Health Sciences reviewed 74 studies on fluoride exposure and children’s IQ conducted in 10 countries, including India.

The same scientists helped formulate an official government recommendation in August that there is “moderate confidence” that higher levels of fluoride are linked to lower IQ scores.

Now, the team led by Kyla Taylor said the analysis found a “statistically significant association” between fluoride exposure and reduced IQ scores.

The review estimated that for every 1 mg/L increase in urinary fluoride, children’s IQ drops by 1.63 points.

Fluoride’s neurotoxicity at high doses is well known, but the controversy lies in the study’s suggestion that exposure below 1.5 mg/L — currently the World Health Organisation’s safety limit — may also affect children’s IQ.

However, the paper doesn’t clarify how much lower than 1.5 mg/L could be dangerous.

Steven Levy, a member of the national fluoride committee for the American Dental Association, raised significant concerns about the study’s methodology.

He pointed out that 52 of the 74 studies reviewed were rated “low quality” by the authors themselves but were still included in the analysis.

“Almost all of the studies have been done in other settings where there are other contaminants, other things we call confounding factors,” he told AFP, citing coal pollution in China as an example.

Levy also questioned the study’s use of single-point urine samples instead of 24-hour collections, which provide greater accuracy, as well as the challenges in reliably assessing young children’s IQ.

With so many uncertainties, Levy argued in an editorial accompanying the study that current policies “should not be affected by the study findings.”

That said, the journal also published an editorial commending the study for its methodological rigour.

The benefits of water fluoridation are well documented. Introduced in the US in 1945, it quickly reduced cavities in children and tooth loss in adults, earning recognition from the Centers for Disease Control and Prevention as one of the greatest public health achievements of the 20th century.

Fluoride, which also occurs naturally in varying levels, helps restore minerals lost to acid breakdown in teeth and reduces acid production by cavity-causing bacteria.

However, with fluoride toothpastes widely available since the 1960s, some research suggests diminishing returns.