Water fluoridation 'a safe way of stopping tooth dec...

"Adding fluoride to tap water could save the NHS millions and dramatically improve children's dental health," the Mail Online reports. A new UK study concluded that water fluoridation is a "safe and effective" way of preventing tooth decay in children.

The study used national data to compare the rates of tooth decay and other health outcomes in areas of England where fluoride either has or has not been added to the water.

Primarily, the study seems to confirm what is already well established – fluoride protects against tooth decay. Rates of tooth decay among five and 12-year-olds and hospital admissions for tooth decay in under-fives were significantly lower in water-fluoridated areas.

Whether fluoride could have detrimental effects on other areas of health has been a concern. This study didn't find an adverse effect for any of the outcomes examined. In fact, water fluoridation was linked to small decreases in the rates of bladder cancer and kidney stones, and a tiny reduction in all-cause death. There was also no evidence water fluoridation increased the rates of children born with Down's syndrome.

But we should not automatically assume water fluoridation is protective against bladder cancer, kidney stones and death, as the differences in rates are quite small and could be accounted for by many unmeasured factors.

Overall, the study lends support to the positive effects of water fluoridation on dental health among young children. However, firmer conclusions on possible wider health effects cannot be made.

Where did the story come from?

The study was carried out by researchers from Public Health England (PHE) and was published in the peer-reviewed journal of Community Dentistry and Oral Epidemiology. No sources of financial support are reported.

In the interests of transparency, it should be made clear that Bazian Ltd carried out an independent analysis of key research submitted to South Central Strategic Health Authority as part of the public consultation on the proposal to fluoridate water in Southampton.

The Mail's coverage is generally accurate, though their article focuses on the effects of child tooth decay. It doesn't cover the aim of this research – to look into other health effects – or cover the limitations of the evidence. Saying that "putting fluoride in the water everywhere would save the NHS millions" is only an assumption. The article also doesn't recognise that in some parts of the UK, fluoride naturally occurs at the recommended levels.

What kind of research was this?

This was a cross-sectional study that aimed to look at the association between water fluoridation schemes in England and selected health outcomes.

Six million people in England are said to live in areas where the level of fluoride in water has been adjusted, the main reason being to reduce the public health burden of dental caries. Dental caries, or tooth decay, are reported to affect more than one-quarter of young children, with higher rates in areas of greater deprivation.

Fluoride has long been recognised to reduce the risk of dental caries. Water fluoridation schemes in England (mostly introduced from the late-60s to mid-80s) aim to achieve a level of one part fluoride per million (1ppm) in water, with a maximum permitted level of 1.5ppm.

However, while the dental effects of fluoride are well established, what is less known is whether fluoride could have other detrimental health effects or, conversely, possible health benefits. This study aimed to compare rates of dental and other health outcomes in areas of England with and without water fluoridation.

What did the research involve?

This study used geographical information systems (computer systems used to track and assess data for defined geographical regions) and known patterns of water supply to estimate the level of exposure to fluoridated water in small areas and administrative districts in England.

Fluoride exposure was estimated for small areas (lower super output areas, LSOAs) with a population range of 1,000-3,000, and for administrative districts known as upper tier local authorities (UTLAs) and lower tier local authorities (LTLAs). Areas where the level of fluoride in water naturally reached around 1ppm without added fluoride were excluded.

Health outcomes examined for the regions (and their data source) were as follows:

dental caries at five and 12 years old – National Dental Epidemiology Programme for England
hospital admissions for dental caries in young children aged one to four years – 2012 Annual Report of the Chief Medical Officers
hip fractures – Hospital Episode Statistics (HES) data
kidney stones – HES data
Down's syndrome – National Down syndrome Register
bladder cancer – English Cancer Registration
bone cancer – English Cancer Registration
overall cancer – English Cancer Registration
all-cause death – Office for National Statistics

The time period in which these outcomes were assessed varied for the individual outcome, but was mostly in the 2000s, up to 2010-13.

The associations between water fluoridation and these outcomes were adjusted for potential confounding factors of deprivation and ethnicity. With the exception of child dental caries, other outcomes were also adjusted for age and gender. Down's syndrome was only adjusted for mother's age.

What were the basic results?

Around 1 in 10 of the LSOAs, LTLAs and UTLAs in England have water fluoridation schemes.

Looking at the dental outcomes, water fluoridation was associated with a significant reduction in the odds of child dental caries (28% reduction for five-year-olds and 21% for 12-year-olds). The rate of hospital admission for dental caries was 42 per 100,000 young children in fluoridated areas, compared with 370 in non-fluoridated areas. This was calculated as a 55% risk reduction.

Looking at other health outcomes, three statistically significant associations were found. Water fluoridation was associated with a reduction in the number of cases of bladder cancer and kidney stones (both 8% reduced incidence) and a small reduction in all-cause death (1.3% reduction).

There were no other associations found for any other health outcomes.

How did the researchers interpret the results?

The researchers concluded that: "This study uses the comprehensive data sets available in England to provide reassurance that fluoridation is a safe and highly effective public health measure to reduce dental decay.

"Although lower rates of certain non-dental outcomes were found in fluoridated areas, the ecological, observational design prohibits any conclusions being drawn regarding a protective role of fluoridation."

Conclusion

This cross-sectional study used reliable national data on water fluoridation areas and linked this to registries and databases to see how this influenced the rate of different health outcomes.

Primarily, the study seems to confirm what is already quite well established – fluoride protects against tooth decay. The rate of tooth decay among young children is a particular concern and is a widespread problem across the UK. The study found rates of tooth decay among five and 12-year-olds and hospital admissions for tooth decay in under-fives were significantly lower in fluoridated areas.

The study also aimed to look at whether water fluoridation has any detrimental health effects. It didn't find an adverse effect for any of the outcomes examined. In fact, water fluoridation was associated with decreased rates of bladder cancer and kidney stones. A reduction in all-cause mortality was also found, though this was tiny.

There are, however, important points to keep in mind:

This type of study cannot prove cause and effect. Given the known effect of fluoride on dental health, the reduction in rates of child tooth decay in fluoridated areas could be directly attributed to water fluoridation. But this link is not certain. For other health outcomes – as the researchers rightly acknowledge – you can be less sure. You cannot say from this study that fluoridating water definitely protects against bladder cancer or kidney stones, even less so from mortality risk. The risk decreases are relatively small, and there may be many other factors that account for the differences the study has not been able to examine.
For rates of child tooth decay, data is limited to the National Dental Epidemiology Programme for England, which gives information only for five and 12-year-olds. Though these may be representative, this still does not cover all children. For under-fives, dental health has been assessed through hospital admissions for tooth decay. This would not cover children who may have tooth decay, but are not admitted to hospital for extractions.
The study did not examine an exhaustive list of other health effects. Fluoride may have effects on other areas of health that this study has not examined.
The study examined by water fluoridation area. But there is no certainty that the people living in these areas have always lived here. You don't know about their water exposure in other areas of the UK, or elsewhere.
Even if individuals had always resided in the area assessed, individual exposure could still vary widely. For example, some people could be drinking regular glasses of tap water throughout the day, while others may not.
Also, as the researchers say, they were not able to account for how long the water fluoridation scheme has been in place, which will vary between areas.

Overall, this study lends support to the positive effect of water fluoridation on dental health among young children. However, firmer conclusions on possible wider health effects cannot be made.