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A new decades-long study has found that exposure to recommended levels of fluoride in drinking water had no negative effect on childhood cognition – and, also, did not contribute to cognitive decline as participants aged. The work, which tracked more than 26,820 participants from 1,020 American high schools between 1980 and 2021, suggests that fluoride exposure may even have had a slight positive effect on cognition early in life. Fluoridated water revolutionized dental health when it was first introduced in 1945. Today, fluoridation is controversial because some research has suggested it may have adverse consequences, including harming childhood cognition. Notably, these prior findings have only reported neurodevelopmental defects upon exposure to extremely high levels of fluoride far above the standard level in American water systems. Now, John Robert Warren and colleagues have shown that high school students in the United States experienced no adverse effects from drinking water with the recommended level of fluoride (0.7 milligrams per liter). They analyzed data from reading comprehension, mathematics, and vocabulary tests given to students from 1,020 secondary schools in 1980 – only some of whom had grown up drinking fluoridated water – who were participants in the “High School and Beyond” cohort. They then followed up with a subset of the participants several times using another global cognitive functioning assessment, ceasing follow-ups in 2021 when most participants had reached age 60. They compared these cognitive data with documented fluoridation practices and fluoride water levels in the towns where the participants lived at the study’s start. These records came from the U.S. Department of Health and Human Services' Fluoridation Census and the U.S. Geological Survey. Of this dataset, 556 municipalities started fluoridating before or during 1980. Another 404 municipalities did not fluoridate at all, while still others varied in fluoridation practices. Through statistical and attributional analyses, Warren et al.determined that children experienced no negative effects from drinking fluoridated water. In fact, they linked fluoride exposure to slightly better cognition at that stage of life, although this cognitive edge became insignificant as participants reached 60. “Until clear evidence exists that water fluoridation lacks public health benefit or compelling evidence of harm at the level of fluoride exposure in fluoridated water, neither of which has occurred, it seems foolhardy to interfere with a long-established and well-recognized public health success,” David Savitz cautions in a related Focus.
Expert Reaction
These comments have been collated by the Science Media Centre to provide a variety of expert perspectives on this issue. Feel free to use these quotes in your stories. Views expressed are the personal opinions of the experts named. They do not represent the views of the SMC or any other organisation unless specifically stated.
Associate Professor Matthew Hobbs, Adjunct Researcher in the Faculty of Health, University of Canterbury
"From a public health perspective, this matters. Community water fluoridation remains one of the most equitable and cost-effective ways to prevent tooth decay, particularly for children and for communities with limited access to dental care. This new evidence reinforces that we can continue to deliver these benefits without compromising cognitive health at any stage of life. It strengthens the case for maintaining fluoridation as a cornerstone of population-level oral health policy as outlined in the World Health Organisation's Global Strategy and Action Plan on Oral Health 2023–2030. These findings reinforce the conclusions of the New Zealand Prime Minister’s Chief Science Advisor’s recent review, which found no credible evidence of neurodevelopmental harm at fluoridation levels used in Aotearoa."
Dr Justin Wall (Te Rarawa, Te Aupōuri), tumuaki of Te Rōpū Niho Ora and practising dentist
“This research demonstrates that fluoridation is safe for all ages, and with the growing older population who have retained their teeth we need to protect their dentition as they age.
“The paper is entirely consistent with the information that has been gathered over many, many, many years of studying the fluoride supplementation of the domestic water supply.
“The principal thing that is always to be examined is whether or not there is any harmful effect of the fluoride supplementation. And this paper clearly demonstrates that there is no harm. Information around or research around the efficacy of fluoridation of the water supply is beyond doubt, and has been well and truly established for many, many years. And the concern the public will always have is that something that is applied to them, whether or not that is harmful, and this research clearly demonstrates that that is not the case. So, it’s a refreshing piece of research, and in particular because it has gone on for such a long period of time, and it has gone on in a country that is profoundly litigious. So, for this amount of research to be done over such a long period of time in America, I think it has to be taken seriously.
“I think that the research itself can be applied internationally. It's not something that's simply restricted to the environment in America. It is something that is well and truly applicable to New Zealand, and this research should go all the way to reassure the public of New Zealand and the municipal authorities who are being charged with implementing the fluoridation of the water supply that this is a safe and effective means of protecting the health of all New Zealanders.
“Furthermore, the health system, as we know, is under pressure, and any measure that can be taken to reduce the pressure on the health system, across the board, needs to be supported. And without a doubt that is the case with fluoridation.”
Professor Jonathan Broadbent, Professor of Dental Epidemiology and Public Health, University of Otago
"The US study addresses an important knowledge gap, as few studies have investigated this issue. It is reassuring that no association was found. This is consistent with findings from a recent Australian study and an older NZ study. However, some other studies have found associations between fluoride and cognitive issues, generally at higher concentrations than used in fluoridation programmes.
"There has been limited recent New Zealand research on community water fluoridation. With new fluoridation programmes being launched in New Zealand ongoing research is greatly needed; this is a necessary part of stewardship in running public health interventions such as fluoridation. New fluoridation programmes in NZ have been focused on areas with higher proportions of deprived New Zealanders and so should have good benefits for oral health, which tends to be worse in areas with greater deprivation. On the other hand, other health issues that occur at greater rates in deprived areas so spurious associations could be found. It is essential that the outcomes of these new programmes are monitored carefully."
