Study reveals effects of exposure to fluoride in drinking water on lifelong cognition: ScienceAlert

Fluoride does a ton of good for your teeth, but its inclusion in drinking water is not without controversy.

While there is no doubt about its ability to prevent tooth decay, public concerns about fluoride’s potential dangers have fueled opposition to water fluoridation for decades, with Utah and Florida becoming the first U.S. states to ban water fluoridation last year.

Are these concerns justified? Not according to a new study from Journal of Dental Researchat least when it comes to concerns that fluoride in drinking water could impact brain function.

Irish researchers analyzed data from the Irish Longitudinal Study of Aging (TILDA), assessing the health of around 2,500 older people in Ireland, with an average age of 65, whose exposure to fluoridated drinking water could be traced over at least 50 years of their lives.

Depending on where they lived during their lives, their exposure to fluoride differed due to varying levels of fluoride concentrations in local water supplies throughout Ireland, which introduced nationwide water fluoridation in 1964.

When researchers divided participants into low, medium and high exposure groups – determined by where they lived – and compared them to outcomes 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 found in drinking water does not appear to be associated with poorer cognitive function later in life.

“Our results provide reassurance that lifetime exposure to fluoridated drinking water at the levels used in Ireland is not associated with poorer cognitive function in older people,” says lead author and public health researcher Vinay Sharma from Trinity College Dublin.

“This is an important public health issue, 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 subgroup of the youngest participants had been exposed to fluoridated drinking water during the first five years of their life, but this early exposure to fluoride also showed no association with cognitive performance.

The researchers point out, however, that only 5% of their sample (124 individuals) were exposed early in their lives, which limits the strength of their conclusions on this aspect.

It’s also worth noting that their finding of no link between fluoride and cognitive decline doesn’t necessarily prove that fluoride is harmless to brain health – just that it’s impossible to find evidence of such harm.

The findings are consistent with a body of previous research that may also detect the lack of a link between fluoridated drinking water and cognitive function.

Not all studies agree, with two studies in China linking fluoride to cognitive impairment in older adults, although outcomes related to excessive fluoride exposure (fluorosis) are not directly comparable.

Similarly, a meta-analysis in 2025 linked fluoride to lower IQ scores in children, although some evidence involved high concentrations beyond those normally used in water fluoridation.

At normal levels, the new findings strengthen the argument that fluoridated drinking water is safe for the brain.

“Fluoridation is one of the most effective tools we have for reducing tooth decay at a population level,” says dental researcher Michael Crowe of Trinity College Dublin. “So it’s important that we now have long-term Irish evidence showing that it costs nothing in terms of cognitive health.”

The results are reported in the Journal of Dental Research.