Comparing the Cochrane and NZ Fluoridation Reviews

Sci Rev

New Zealand policy makers and health professionals should be wary about much of the current media comments on the Cochrane Fluoridation Review (Iheozor-Ejiofor 2015). Anti-fluoridation campaigners are misrepresenting it and distorting its findings. They are using cherry-picked quotes to make claims about the review which are just not true.

Some are even claiming (wrongly) that the Cochrane review findings conflict with this in the NZ Fluoridation Review (Eason et al., 2014). Or that, simply because it was published a few months after the NZ Review it somehow makes the NZ Review obsolete.

Review findings agree

Nothing could be further from the truth. The findings in the Cochrane Review do not conflict with those in the NZ  Review. And, because the Cochrane Review is much more limited than the NZ Review, policy makers and health professionals should not consider that as the only document required for their reading.

In particular, the Cochrane Review considered only questions of community water fluoridation (CWF) efficacy. It did not consider aspects related to health concerns which, of course, are always in the front of the minds of policy makers and health professionals.

I have done a side-by-side comparison of the two reviews and summarise their findings below

CWF efficacy

The Cochrane reviewers produced a quantitative estimate for the effect of CWF on dental decay, but only for children and used only studies satisfying their strict selection criteria (see Cochrane fluoridation review. I: Most research ignored). This unfortunately excluded more recent high-quality cross-sectional studies.

The NZ Reviewers did not produce an overall quantitative estimate but made more general conclusions.

Cochrane Review

NZ Fluoridation Review

Efficacy of CWF
“Data suggest that the introduction of water fluoridation resulted in a 35% reduction in decayed, missing or filled baby teeth and a 26% reduction in decayed, missing or filled permanent teeth. It also increased the percentage of children with no decay by 15%. These results indicate that water fluoridation is effective at reducing levels of tooth decay in both children’s baby and permanent teeth”. “Analysis of evidence from a large number of epidemiological studies and thorough systematic reviews has confirmed a beneficial effect of CWF on oral health throughout the lifespan. This includes relatively recent studies in the context of the overall reduced burden of caries that has resulted from the widespread use of topical fluoride products (e.g. toothpastes,  mouth rinses, and fluoride varnishes).”
Adult caries
No conclusions because of study selection limitations. “Although most studies of the effects of CWF have focused on benefits in children, caries
experience continues to accumulate with age, and CWF has also been found to help reduce the extent and severity of dental decay in adults, particularly with prolonged exposure. The long history of CWF around the world now means that many adults in late life have experienced a lifetime of fluoridation. The benefits for adult dental health include lower levels of root caries, and better tooth retention into old age.”
Socio-economic effects
No conclusions because of study selection limitations. “The burden of tooth decay is highest among the most deprived socioeconomic groups, and this is the segment of the population for which the benefits of CWF appear to be greatest. CWF appears to be most cost-effective in those communities that are most in need of improved oral health. In New Zealand, these include communities of low socioeconomic status, and those with a high proportion of children or Māori. A number of studies have suggested that the benefits of CWF are greatest among the most deprived socioeconomic groups, although the magnitude of the difference is uncertain.”
Effect of stopping fluoridation
No conclusions because of study selection limitations. “Stopping CWF leads to ~17% increase in caries experience”  cited from US Task Force on Community Preventive Services
Influence of fluoridated toothpaste, etc.
No conclusions because of study selection limitations. The beneficial effect of CWF on oral health is still shown in relatively recent studies illustrating the overall reduced burden of caries that has resulted from the widespread use of topical fluoride products (e.g. toothpastes,  mouth rinses, and fluoride varnishes). “In New Zealand, significant differences in decay rates between fluoridated and non-fluoridated communities continue to exist, despite the fact that the majority of people use fluoride toothpastes.”

Health issues related to CWF

Dental fluorosis is generally considered the only negative health results of CWF. Both Reviews did consider dental fluorosis, although the Cochrane review did not specifically compare fluoridated and unfluoridated areas – which is necessary to determine the effect of fluoridation on dental fluorosis prevalence. See Cochrane fluoridation review. III: Misleading section on dental fluorosis for a discussion of this and an estimate fo the effect of CWF on dental fluorosis calculated using the Cochrane data.

The Cochrane review did not consider any other health effects.

Cochrane Review

NZ Fluoridation Review

Dental Fluorosis
Only calculated effect of fluoride intake in dental fluorosis. The effect of CWF itself was not considered. However, this can be estimated by subtracting prevalence for unfluoridated region. These estimates indicate that dental fluorosis levels of aesthetic concern are similar in fluoridated and unfluoridated areas (see Cochrane fluoridation review. III: Misleading section on dental fluorosis).
“The prevalence of fluorosis of aesthetic concern is minimal in New Zealand, and is
not different between fluoridated and non-fluoridated communities, confirming that a substantial proportion of the risk is attributable to the intake of fluoride from sources other
than water (most notably, the swallowing of high-fluoride toothpaste by young children).
The current fluoridation levels therefore appear to be appropriate. It is important, however, that the chosen limit continues to protect the majority of high-exposure individuals.”
IQ effects
Not considered “We conclude that on the available evidence there is no appreciable effect on cognition arising from CWF.”
Not considered “We conclude that on the available evidence there is no appreciable risk of cancer arising from CWF.”
Not considered “Studies and systematic reviews have found no evidence that consumption of optimally fluoridated drinking water increases the risk of developing kidney disease. However, individuals with impaired kidney function experience higher/more prolonged fluoride exposure after
ingestion because of reduced urinary fluoride excretion, and those with end stage kidney
disease may be at greater risk of fluorosis.”


The Cochrane review is far more limited in its coverage than the NZ Fluoridation Review. It did not consider possible health effects (apart from dental fluorosis) which is an important aspect of the fluoridation controversy for health professionals and policy makers.

The two Reviews agree that CWF is effective for children, but the NZ Review also considered effectiveness for adults, the reduction of socioeconomic differences in oral health and effects of stopping fluoridation on tooth decay. It also considered more recent research than the Cochrane review, so was able to discuss possible reduction in the efficacy of CWF due to the use of fluoridated toothpaste in recent years.

The Cochrane review does not make the NZ Fluoridation  Review obsolete at all. Nor do its conclusions conflict with those of the New Zealand Review.

Policy makers and health professionals should pay attention to both reviews in making judgements of CWF efficacy, but will need to use the NZ Review for their judgements on possible health effects.


New Zealand Fluoridation Review:
Eason, C., & Elwood, JM. Seymour, Thomson, WM. Wilson, N. Prendergast, K. (2014). Health effects of water fluoridation : A review of the scientific evidence

Cochrane Fluoridation Review:
Iheozor-Ejiofor, Z., Worthington, HV., Walsh, T., O’Malley, L., Clarkson, JE., Macey, R., Alam, R., Tugwell, P., Welch, V., Glenny, A. (2015). Water fluoridation for the prevention of dental caries (Review). The Cochrane Library, (6).

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3 responses to “Comparing the Cochrane and NZ Fluoridation Reviews

  1. What a load of codswallop Ken . . . all ‘policy makers and health professionals’ need to do is remember the Nuremburg Trials and what happened to those other Nazis that trampled over the rights of other to decide what happens to their bodies . . . :}


  2. You’ve missed the point, hopefully not deliberately. In summary, the Cochrane review found that there were essentially no recent AND independent studies supporting water fluoridation as a community benefit.

    Given the Cochrane Foundation’s purposes, we can safely draw the conclusion that if NZ has presented recent supporting studies, they were too biased for the Cochrane review to include them. 100 biased studies are not scientific proof – nor are 1000 biased studies.

    Cochrane Review’s Conclusion…

    “There is very little contemporary evidence, meeting the review’s inclusion criteria, that has evaluated the effectiveness of water fluoridation for the prevention of caries.

    The available data come predominantly from studies conducted prior to 1975, and indicate that water fluoridation is effective at reducing caries levels in both deciduous and permanent dentition in children. Our confidence in the size of the effect estimates is limited by the observational nature of the study designs, the high risk of bias within the studies and, importantly, the applicability of the evidence to current lifestyles. The decision to implement a water fluoridation programme relies upon an understanding of the population’s oral health behaviour (e.g. use of fluoride toothpaste), the availability and uptake of other caries prevention strategies, their diet and consumption of tap water and the movement/migration of the population. There is insufficient evidence to determine whether water fluoridation results in a change in disparities in caries levels across SES. We did not identify any evidence, meeting the review’s inclusion criteria, to determine the effectiveness of water fluoridation for preventing caries in adults.

    There is insufficient information to determine the effect on caries levels of stopping water fluoridation programmes.

    There is a significant association between dental fluorosis (of aesthetic concern or all levels of dental fluorosis) and fluoride level. The evidence is limited due to high risk of bias within the studies and substantial between-study variation”

    Liked by 1 person

  3. Minimal – actually I think it is you that has missed the point. The point being the very restrictive selection criteria used by Cochrane.

    While this enabled them to provide a quantitative estimate of the efficacy of CWF for children they just did not have the studies “meeting the review’s inclusion criteria” to say much else. Although in the discussion the reviewers did refer to other recent studies they had excluded – and made the comment that much of the recent work they excluded was of high quality and allowed for excluding confounder effects because of computer use and modern statistical analysis.

    It would be extremely biased for you conclude what you do. I suggest you read the full text of the Cochrane Review – the Abstract and Plain Language Summary do not include the qualifications and explanations made in the full text and discussion.

    You could also look at my articles discussing the Cochrane review in detail.

    You should also read the NZ Fluoridation review before slagging it off in this manner.


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