Divisive US study finds link between fluoride and childhood IQ loss

WASHINGTON - A controversial new study released on Jan 6 in a US medical journal could reignite debate over fluoride’s safety in water, linking higher exposure levels to lower IQ in children.

Published in the prestigious Journal Of The American Medical Association Paediatrics, 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 US water fluoridation levels.

Its release comes as US President-elect Donald Trump prepares to take office.

His health secretary nominee, Mr Robert F. Kennedy Jr, is

a vocal critic of fluoridated water,

which currently serves more than 200 million Americans, or nearly two-thirds of the 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 Canada, China and India.

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

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

Specifically, the study estimates that for every 1mg per litre increase in urinary fluoride – a marker of overall exposure – children’s IQ drops by 1.63 points.

Study limitations

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

Crucially, the paper does not clarify how much lower than 1.5mg per litre could be dangerous, leaving questions about whether the US guideline of 0.7mg per litre needs adjustment.

The authors acknowledged that there was “not enough data to determine if 0.7mg per litre of fluoride exposure in drinking water affected children’s IQ”.

Professor 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.

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

The journal also published an editorial commending the study for its methodological rigor.

Balancing gains against risks

On the other side of the debate, 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 Centres 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, reduces acid production by cavity-causing bacteria, and makes it harder for these bacteria to stick to the teeth.

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

Proponents argue fluoridation reduces socio-economic disparities in dental care, while critics warn it may pose greater risks of neurological harm to vulnerable communities.

“Evidence on the effects of adjusting levels of fluoride or interrupting community water fluoridation programmes is critically needed, especially within the context of the US,” Dr Fernando Hugo, chairman of the New York University College of Dentistry, told AFP. AFP