Water Fluoridation Does Not Impair Brain Function

Researchers in Ireland found no association between lifetime exposure to fluoridated drinking water and cognitive decline in older adults, according to coverage from Irish Medical Times, UA.NEWS and ScienceAlert. The study, published in the Journal of Dental Research as Lifetime Fluoride Exposure and Cognition in Older Irish Adults, used data from the Irish Longitudinal Study on Ageing (TILDA) covering 2,495 participants with an average age of 65.

The team estimated how much fluoride each participant had likely consumed from drinking water over their lifetime by tracking where they had lived and matching those addresses to national water fluoride concentration records going back many years, down to infancy in some cases. Ireland introduced community water fluoridation in 1964 as a public health measure to prevent tooth decay, and fluoride concentrations varied between local water supply systems. Participants were grouped by how much of their lives had been spent drinking fluoridated water, from low to high exposure, and took two standard cognitive tests used in dementia research. Scores did not differ between any of the exposure groups, UA.NEWS reported.

Lead author Dr Vinay Sharma of Trinity College Dublin said the 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." He added that the study "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 programme in Ireland, and internationally." Sharma said most previous studies looked at fluoride exposure over a short window, in childhood or adulthood, rather than tracking it continuously across a life and then testing cognition later.

A subgroup of the youngest participants had been exposed to fluoridated water in their first five years of life, and no association with cognitive scores was found there either. But that group accounted for only 5% of the sample, 124 people, which limits the strength of that conclusion, UA.NEWS and ScienceAlert reported.

The researchers also noted that the study focused on household water fluoride concentration without accounting for other sources of fluoride a person ingests. ScienceAlert stressed that finding no link does not prove fluoride is harmless to brain health, only that evidence of such harm was not found. Two studies in China linked cognitive impairment in older people to excessive fluoride exposure and fluorosis, which are not directly comparable with the Irish data, and a 2025 meta-analysis linked fluoride to lower IQ scores in children, though some of that evidence involved concentrations exceeding those normally used in water fluoridation.

Principal investigator Prof Lina Zgaga said Ireland's national fluoridation policy creates an opportunity for high-quality research, and that contemporary evidence is essential to support informed decisions about the intervention nationally and internationally. Co-PI Dr Michael Crowe of Dublin Dental University Hospital said fluoridation has been "one of the most effective tools we have for reducing tooth decay at a population level." Co-author Prof Brian O'Connell said the Irish population should be checked for adverse effects on an ongoing basis, and that the research "should just be the baseline for future studies."