Long in the tooth: is water fluoridation out of date?

One ongoing intervention to tackle tooth decay in parts of the UK is the provision of fluoride in drinking water. But such moves aren’t always popular with the communities involved.  There is also a lack of evidence based on contemporary populations. Here, Dr Michaela Goodwin and Professor Michael Kelly from The University of Manchester outline the findings of a new study into water fluoridation, its effectiveness in improving dental health, and whether it is good value for money.

• Fewer than 10% of people in the UK receive fluoridated water – with no new schemes since the 1980’s.
• New research suggests fluoridation schemes are a cost-effective method of reducing tooth decay in children.
• However, policymakers may want to focus on targeted interventions for deprived communities, rather than new fluoridation schemes.

Water fluoridation (WF) is intended to reduce the incidence of dental caries, including among children and young people. It involves the addition of fluoride, a naturally occurring mineral, to drinking water. Fluoride works by strengthening tooth enamel and creates an environment in the mouth which helps to make teeth more resistant to decay.

The Health and Care Act 2022 gave the Secretary of State for Health the power to implement – or terminate – water fluoridation schemes in England. Previously, this power had rested with local authorities. About six million people in England live in areas with WF, predominantly in the Midlands and the North East.

WF has historically been considered a low-risk, low-cost method of improving dental health. The side effect most commonly associated with such schemes is dental fluorosis; a mottling of the teeth which can lead to a spotty or stripy appearance. Research in the US and UK in the 20th century showed that WF can significantly reduce the levels of tooth decay. However, the introduction of fluoride toothpastes has also been linked to large improvements in dental health. The question for policymakers and public health officials is, in the 21st century, does WF still represent the best intervention to prevent tooth decay?

Cumbria – a case study

To investigate the effectiveness and cost-effectiveness of WF, researchers from The University of Manchester undertook a study in Cumbria (CATFISH), where WF was reintroduced in some areas in 2013. Following two groups of children – one born in 2014/15, and one born in 2008/9 – for five years, the study compared the occurrence of dental caries in children living in areas with WF against those in non-WF regions.

For the younger group of children, there was an absolute difference of 4% in the incidence of caries between the groups, with a lower incidence in the group receiving water fluoridation (17.4% vs 21.4%). For the older cohort, there was about a 3% point difference in the incidence of caries between the groups (19.1% vs 21.9%), though there was not enough evidence to determine if this was due to chance. For both groups, water fluoridation had the same effect regardless of whether the children were from a wealthy or disadvantaged background. In both groups, it was determined that WF likely represented value for money, using the NICE threshold of £20,000 per Quality Adjusted Life Year (QALY).

However, these findings must be seen in the wider context of diminishing levels of dental caries over the last 30 years. In the relatively deprived population involved in this study, approximately 20% of children experienced tooth decay; in earlier decades it had been as high as 72%. The prevalence of dental decay varies across the country, from 34% of five year olds in the more deprived areas to 14% in the less deprived areas – a national average of 23%. Much of the evidence base for WF was established before the introduction of fluoride toothpastes, making it difficult to gage the impact of WF on a modern population.

The context and developments which occurred during the study must also be considered. During December 2015, severe flooding in Cumbria resulted in one treatment plant ceasing water fluoridation for a number of months, meaning some individuals taking part may not have received optimal levels of fluoridation consistently. However, previous research has shown that water fluoridation plants are not always consistently fluoridating at the optimum level, and therefore this reflects the current nature of this type of public health intervention.

The CATFISH study only provides evidence for the impact of water fluoridation on those up to the age of 11 years old. The LOTUS study – which will be released in 2023 – has evaluated the impact of fluoridation in adults, and will be a complimentary piece to CATFISH to inform policy and regulation.

The figure of 23% represents an important disease burden – and demonstrates that further intervention is necessary to continue to reduce the number of children experiencing dental decay.

Recommendations

Prevalence levels of dental carries are an important factor to take account of when exploring new WF schemes. Based on this research, policymakers and public health officials might consider targeted approaches in areas where prevalence is lower. When considering population level approaches, the modification of known risk factors, such as sugar consumption, rather than relying on the biopharmaceutical effect of fluoride alone, is important.

Although the attractiveness of what appears to be a simple universal intervention to prevent disease is clear, it is also apparent that the changing epidemiological nature of dental decay will require further consideration in the future. The inability of the public health authorities to introduce a new scheme in the UK in the last 30 years has demonstrated the logistical and political problems of delivering this type of program.

The evidence this study presents suggests that water fluoridation is cost effective, even when used alongside fluoride toothpastes. However, we know that deprived communities are at higher risk of dental caries, and so policymakers and public health officials must consider whether targeted interventions – and focusing on high sugar consumption as opposed to the broad approach of new water fluoridation schemes – would represent better value for money.

This project was funded by the National Institute for Health Research Public Health Research Programme (project number 12/3000/40). The views and opinions expressed therein are those of the authors and do not necessarily reflect those of the NIHR PHR Programme or the Department of Health and Social Care.

The CATFISH study was a collaborative piece of research between The University of Manchester, the University of Cambridge, and King’s College London.

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