New research from Trinity College Dublin shows no link between exposure to community water fluoridation (CWF) and later-life cognitive function in older Irish adults. The research also found no evidence that exposure in early childhood had any impact either.
CWF was introduced in Ireland in 1964 as a public health measure to prevent tooth decay. It has proven effective at this, but in recent years there has been growing public debate about whether fluoride could have a negative effect on brain health and development.
The researchers used data from the Irish Longitudinal Study on Ageing (TILDA) to calculate how much fluoride each of 2,495 older adults (average age 65) had likely consumed from drinking fluoridated water over their lifetime. They tracked where they had lived and matched this to national water fluoride concentration records going back many years, down to infancy in some people.
Participants were grouped by how much of their lives had been spent drinking fluoridated water, from low to high exposure, and were given two standard cognitive tests used in dementia research. Scores did not differ between any of the exposure groups, suggesting no link between CWF and cognition in older adults.
“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,” said Dr Vinay Sharma, from Trinity’s School of Medicine , who is lead author of the study, just published in the Journal of Dental Research.
“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 programme in Ireland and internationally.”
“Most previous studies have only looked at fluoride exposure over a short window, either in childhood or in adulthood, rather than tracking it continuously across a person’s life and then testing cognitive function later on. That’s what sets this study apart.”
Trinity’s Professor Lina Zgaga, PI of the study , said: “Ireland is unusual because it has a national policy of community water fluoridation. This creates an opportunity to do high-quality research in large studies and answer many outstanding questions around fluoridation. Having good, contemporary evidence is essential to support informed decisions about this public health intervention nationally and internationally, and to ensure that policy continues to be based on the best available evidence.”
“Fluoridation has been one of the most effective tools we have for reducing tooth decay at a population level, so it matters that we now have long-term Irish evidence that it isn't costing anything in terms of cognitive health,” added Dr Michael Crowe, Co-PI of the study.
What is the potential impact of this research?
The findings, combined with the established dental health benefits of fluoridation for children and adults, support the continued use of CWF as a public health intervention.
“Nonetheless, we should continue to check for any adverse effects of water fluoridation in the Irish population on an ongoing basis. This research establishes a way to monitor the health of water consumers but should just be the baseline for future studies,” according to Professor Brian O’Connell , another co-author of the research.
One limitation is that this study focused on household water fluoride concentration, but there are other factors that contribute to the total amount of fluoride a person ingests. The researchers also highlight that the study’s ability to detect any effect of early-life exposure was limited, as only 5% of participants had been exposed to fluoridated water in early childhood - the fluoridation programme began in 1964, so many participants were already older than five by the time it started in Ireland.
The present analysis was funded by the Health Research Board (Ireland) Secondary Data Analysis Project Award. Data were used from Wave 3 of TILDA (2014–2015), which was funded by the Department of Health (Ireland) and Atlantic Philanthropies. The collection of historical address data and the estimation of lifetime fluoride exposure for TILDA participants was supported by a Health Research Board (Ireland) Applied Partnership Award.
Journal of Dental Research