The dental health benefits of adding fluoride to drinking water may be smaller now than before fluoride toothpaste was widely available, a review suggests.
Researchers from the universities of Manchester, Dundee and Aberdeen assessed evidence from 157 studies comparing communities that had fluoride added to their water supplies with communities that had no additional fluoride in their water.
The review found that the benefit of fluoridation had declined since the 1970s, when fluoride toothpaste became more widely available.
Fluoride is known to reduce tooth decay. The addition of low levels of fluoride to drinking water has long been considered one of the greatest public health achievements of the last century.
“When interpreting the evidence, it is important to think about the wider context and how society and health have changed over time,” said Anne-Marie Glenny, a professor of health sciences research at the University of Manchester and a co-author of the review.
“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.”
Results from studies conducted after 1975 suggest that water fluoridation schemes may lead to slightly less tooth decay in children’s baby teeth.
Analysis of these studies, covering a total of 2,908 children in the UK and Australia, estimated that fluoridation may lead to an average of 0.24 fewer decayed baby teeth per child. However, the estimate comes with uncertainty, meaning it is possible that more recent schemes have no benefit, the researchers said.
By comparison, an analysis of studies with 5,708 children conducted in 1975 or earlier estimated that fluoridation reduced the number of decayed baby teeth on average by 2.1 per child.
The Cochrane review was only able to draw conclusions about the impact on children’s teeth, with similar findings across baby and permanent teeth. There were no studies with adults that met the review’s criteria.
“The evidence suggests that water fluoridation may slightly reduce tooth decay in children,” said another co-author, Dr Lucy O’Malley, a senior lecturer in health services research at the University of Manchester.
“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.”
Advocates have suggested that one of the key benefits of water fluoridation is that it reduces oral health inequalities. The review sought to examine this but did not find enough evidence to support the claim, although the researchers said that did not necessarily mean there was no effect.
“Whilst water fluoridation can lead to small improvements in oral health, it does not address the underlying issues such as high sugar consumption and inadequate oral health behaviours,” said Janet Clarkson, a co-author and professor of clinical effectiveness at the University of Dundee. “It is likely that any oral health preventive programme needs to take a multifaceted, multiagency approach.”
In August, a US government report concluded that fluoride in drinking water at twice the recommended limit was linked to lower IQ in children.
The 324-page report did not reach a conclusion about the risks of lower levels of fluoride, saying more research was needed. It also did not answer what high levels of fluoride may do to adults.
