Fluoride: Assessing the risks to cognitive development

Fluoride has long been the subject of conspiracy theories. In the 1950s, some believed its presence in US tap water was a communist plot to undermine America (famously satirised in the film Dr. Strangelove).

It has also been heavily criticised by politicians, such as US Health Secretary Robert F Kennedy Jr, who has linked it to both bone fractures and cancer.

Such criticisms have even affected law. The US state of Utah will be the first to ban fluoride in its drinking water, despite widespread opposition from dentists and health organisations.

Now, a new study suggests that heavy exposure to fluoride during pregnancy and early in life may harm cognitive development for young children.

The study suggests that “even relatively low concentrations of fluoride can impact children’s early development,” explains Maria Kippler, one of the researchers.

Why is fluoride present in drinking water?

Fluoride is a naturally occuring mineral released into soils and water from rocks.

The mineral is used due to its ability to reduce tooth decay. In many countries, including the US, Ireland, New Zealand, and Chile, the mineral is added to drinking water, in small levels, for this reason. It is also found in toothpaste.

In instances where fluoride has been removed from drinking water, such as in Calgary, Canada and in Israel, dental treatments have increased.

Could it have negative health impacts?

A new study from Karolinska Institutet in Sweden, published in the journal Environmental Health Perspectives, suggests that it might.

The study followed 500 mothers and their children in rural Bangladesh, where fluoride occurs in drinking water naturally at similar concentration to other countries. It explores the relationship between children’s cognitive abilities and early exposure to fluoride.

The cognitive development of the children was evaluated by trained psychologists at five and at ten years of age. Fluoride levels in both mothers and children were assessed by analysing concentration in urine samples.

The results showed that fluoride was linked to cognitive development. Children aged ten with more than 0.72 mg/L were found to have lower verbal reasoning skills and lower ability to interpret and process sensory input than those with less.

No statistically significant correlation between fluoride and cognitive abilities was found in the urine of children aged five, however.

Exposure levels associated with a lower cognitive development were of a lower concentration than those obtained at the 1.5 mg/L threshold given by the EU and WHO (however, the current threshold in the US is 0.7 mg/L).

As an observational study, this is far from conclusive, and more studies are needed. No firm conclusions, in other words, can be drawn about causalities at this stage.

History of fluoride and cognitive development

A range of studies have been done on this subject before this, drawing uncertain conclusions.

A 2023 review in the journal Environmental Research compounded a range of previous studies and found, despite some heterogeneity, a general inverse correlation between fluoride concentration and intelligence in children.

This inverse correlation, according to the review, is already detectable at urine levels corresponding to the US’s minimum threshold of 0.7mg/L in water.

However, the correlation was less clear when analysing the link between concentrations in water itself.

The review concludes that levels of concentration previously considered as safe – 0.7 to 1.2mg/L – can be harmful.

However, it should be noted that the review also analysed risk of bias within the studies it looked at.

Doing this, it found a weaker or even no association between lower IQ and high fluoride in the most ‘carefully conducted’ studies, which took more account of potential confounders such as age and socioeconomic background.

A later study from the University of Queensland, published in December 2024 in the Journal of Dental Research, found no link between cognitive development and fluoride.

This study assessed people aged 16 to 26 on their intelligence levels, in order to ascertain whether early-life exposure to fluoride had had any long-term effects on their development.

It in fact found that those who had been consistently drinking fluoridated water had IQ scores similar, even slightly higher, on average than those who had not.

Even those with dental fluorosis, a condition associated with excessive intake of fluoride, had not been significantly affected cognitively.

In this study, which took place in Australia, factors such as socioeconomic status were taken into account. The study even referenced the earlier review’s finding that confounders often meant the difference between a link and no link.

Whatever the answer, the topic is complex and remains controversial.

Sourced From: Environmental Health Perspectives

‘Prenatal and childhood exposure to fluoride and cognitive development: findings from the longitudinal MINIMat cohort in rural Bangladesh’

Published on: 5 March 2025

Doi: https://doi.org/10.1289/EHP14534

Authors: T. Singh, K. Gustin, S. M. Rahman, S. Shiraji, F. Tofail, M. Vahter, M. Kampouri, and M. Kippler

Sourced From: Environmental Research

‘Fluoride exposure and cognitive neurodevelopment: Systematic review and dose-response meta-analysis’

Published on: 15 March 2023

Doi: https://doi.org/10.1016/j.envres.2023.115239

Authors: F. Veneri, M. Vinceti, L. Generali, M. E. Giannone, E. Mazzoleni, L. S. Birnbaum, U. Consolo, T. Filippini

Sourced From: Journal of Dental Research

‘Early Childhood Exposures to Fluorides and Cognitive Neurodevelopment: A Population-Based Longitudinal Study’

Published on: 18 December 2024

Doi: https://doi.org/10.1177/00220345241299352

Authors: L.G. Do, A. Sawyer, A. J. Spencer, S. Leary, J. K. Kuring, A. L. Jones, T. Le, C. E. Reece and D.H. Ha