Fluoride does a world of good for your teeth, but its inclusion in drinking water is not without controversy.
While there’s little doubt about its ability to help prevent tooth decay, public concerns about fluoride’s potential harms have fueled opposition to water fluoridation for decades, with Utah and Florida becoming the first US states to ban water fluoridation last year.
Are those concerns justified? Not according to a new study in the Journal of Dental Research, at least with regard to fears that fluoride in drinking water might impact brain function.
Researchers in Ireland analyzed data from the Irish Longitudinal Study on Ageing (TILDA), assessing the health of approximately 2,500 older adults in Ireland with an average age of 65, whose exposure to fluoridated drinking water could be traced across at least 50 years of their lives.
Depending on where they lived over the course of their lives, their exposure to fluoride differed due to varying levels of fluoride concentrations in local water supplies across Ireland, which introduced nationwide water fluoridation in 1964.
When the researchers sorted the participants into low-, medium-, and high-exposure groups – determined by residential locations – and compared them with results measured by two different cognitive assessments, there was no link between fluoride exposure and their cognitive performance.
In other words, several decades of exposure to fluoride in drinking water doesn’t appear to be associated with poorer cognitive function in later life.
“Our findings provide reassurance that lifetime exposure to fluoridated drinking water at the levels used in Ireland is not associated with poorer cognitive function in older adults,” says lead author and public health researcher Vinay Sharma from Trinity College Dublin.
“This is an important public health question, and we hope these findings contribute to an evidence-based conversation about the safety of the community water fluoridation program in Ireland and internationally.”
A subset of the youngest participants had been exposed to fluoridated drinking water in the first five years of life, but that early-life exposure to fluoride also showed no association with cognitive performance.
The researchers point out that only 5 percent of their sample (124 individuals) had early-life exposure, however, which limits the strength of their conclusions on that aspect.
It’s also worth noting that their finding of no link between fluoride and cognitive decline does not necessarily prove that fluoride is harmless to brain health – only that evidence of such harm can’t be found.
The findings match up with a body of previous research that could similarly detect no link between fluoridated drinking water and cognitive function.
Not all studies agree, with two studies in China linking fluoride to cognitive impairment in elderly people, although the findings related to excessive fluoride exposure (fluorosis), and are not directly comparable.
Similarly, a meta-analysis in 2025 linked fluoride to lower IQ scores in children, although some of the evidence related to high concentrations exceeding those normally used in water fluoridation.
At normal levels, the new findings strengthen the case that fluoridated drinking water is safe for the brain.
“Fluoridation has been one of the most effective tools we have for reducing tooth decay at a population level,” says dental researcher Michael Crowe from Trinity College Dublin, “so it matters that we now have long-term Irish evidence that it isn’t costing anything in terms of cognitive health.”
The findings are reported in the Journal of Dental Research.
This article was fact-checked by Fiona MacDonald and edited by Fiona MacDonald. While we pride ourselves on our process, we are only human. If you spot a mistake, please let us know.
