Adding fluoride to drinking water may be less effective now than it was in the past, according to a major review.
The benefits of fluoridating water supplies appear to have declined since the 1970s when fluoride toothpaste became widely available in the UK, academics found.
Fluoride has been described as one of the “main weapons in the battle against tooth decay” because of the oral health benefits linked to the mineral, which can be found in soil, food and drink.
Many areas have enough naturally occurring fluoride in drinking water.
In other parts of the country levels are manually adjusted as part of a fluoridation scheme – some 10% of people in England live in areas where fluoride is added to the water, mainly in the West Midlands and the North East.
Researchers said many older studies examining the effects of water fluoridation are “not representative today” so they chose to examine more up-to-date studies on the impact of water fluoridation schemes.
They found that older studies, carried out in or before 1975, showed a “clear and clinically important” effect of reducing the number of decayed, missing or filled teeth.
Water fluoridation reduced the number of decayed, missing or filled teeth by two whole teeth on average among children with their baby teeth, researchers said.
Studied carried out after 1975 show only a “modest” benefit, the authors said.
The benefit noted in contemporary studies is the equivalent of a reduction of a “quarter of a tooth” that is decayed, missing or filled, on average, among children living in areas where fluoride is added to water, according to experts from the Universities of Manchester, Aberdeen and Dundee.
A similar reduction was seen among children with their second set of teeth living in fluoridated areas.
Overall, water fluoridation “may lead to slightly more children being free of tooth decay” and “may lead to slightly less tooth decay in children’s baby teeth”, according to the updated Cochrane Review examining the benefit of such schemes.
[1/2] The #Gvt has announced plans to extend the current water fluoridation scheme in the North East to reach an extra 1.6m people.
Water fluoridation is the single most effective #PublicHealth measure for ⬇️tooth decay – the leading cause of 🏥admissions for 5-9 yr olds. pic.twitter.com/2fozrp7jao
— Association of Directors of Public Health (ADPH) (@ADPHUK) March 25, 2024
Co-author Dr Lucy O’Malley, senior lecturer in health services research at the University of Manchester, said: “The evidence suggests that water fluoridation may slightly reduce tooth decay in children.
“Given that the benefit has reduced over time, before introducing a new fluoridation scheme careful thought needs to be given to costs, acceptability, feasibility and ongoing monitoring.”
The news comes as the Government is considering whether to increase water fluoridation in north-east England.
A consultation was opened early this year on proposals to expand the scheme to cover Darlington, Durham, Gateshead, Hartlepool, Middlesbrough, Newcastle, Northumberland, North Tyneside, Redcar and Cleveland, South Tyneside, Stockton and Sunderland.
Ministers are expected to respond “in due course”.
Professor Anne-Marie Glenny, co author of the paper, also from The University of Manchester, said the data could “inform policymakers” but added: “What we can say from our review, and particularly from the contemporary studies within the review, is that water fluoridation is only having a modest benefit on dental caries, and those benefits may take years to be realised,” she said.
Prof Glenny said water fluoridation should be part of a “comprehensive programme of public health interventions, including those that reduce sugar consumption or other preventative measures”.
She added: “When interpreting the evidence, it is important to think about the wider context and how society and health have changed over time.
“Most of the studies on water fluoridation are over 50 years old, before the availability of fluoride toothpaste. Contemporary studies give us a more relevant picture of what the benefits are now.”
Co-author Tanya Walsh, professor of healthcare evaluation at The University of Manchester, added: “Contemporary evidence using different research methodologies suggest that the benefits of fluoridating water have declined in recent decades.”
Data published by the NHS in September suggests that tooth decay remains the leading cause for hospital admissions among five to nine-year-olds in England – some 19,381 children in this age bracket were admitted to hospital in 2023/2024 because of tooth decay.
The British Dental Association said the new evidence has not changed its assessment that community water fluoridation is a safe and effective public health intervention and should form part of a package of measures to improve oral health.
Mick Armstrong, chairman of its health and science committee, said: “What this new evidence shows is that water fluoridation has a role to play, as one of many tools in the fight against decay.”
Researchers from the latest study said they could not comment on potential harms claimed to be linked to fluoridation, as the study did not examine this.
But experts did say that US reports about fluoride and children’s IQ examined concentrations of fluoride in the water at higher levels than would be seen in a community water fluoridation programme.
Meanwhile, the last version of the Cochrane Review concluded that adding fluoride to water supplies increases the number of people with dental fluorosis – the appearance of fine pearly white lines or flecking on the surface of the teeth.
