One of the overriding themes of the Science Based Medicine blog is to use rigorous science when evaluating any health claim – be it medical, dental, dietary, fitness, or any other assertion put forth with the intention of improving one’s health. Once the scientific evidence is evaluated as to efficacy, there are other criteria which must be taken into consideration, such as ease of administration, costs, possible adverse effects, and so on. Benefits have to be carefully weighed against risks to properly determine any appropriate course of action. For example, if a new pill is developed which is significantly better at , say, managing hypertension than existing medications, but it kills 10% of patients taking it, it obviously would not be the drug of choice. Conversely, if a proposed treatment, say homeopathy, is touted as being 100% safe with no side effects, but has absolutely zero benefits, it too would not be a recommended treatment. It’s a complicated and often ambiguous algorithm, and is imperfect due to the impossibility of attempting to quantify non-quantifiable values and qualities.
The perils and profits of fluoride
And so it is with the never-ending fluoride debate. Fluorosis is the major “risk” of fluoride ingestion, while decay prevention is the primary benefit (ignoring unsubstantiated claims by anti-fluoride groups of fluoride toxicity causing lowered IQ, chronic diseases, and other maladies). I’ve covered this topic before here and with Dr. Clay Jones here, but a new systematic review from the Cochrane Collaboration was recently released, its goal being:
…to assess the effects of water fluoridation (artificial or natural) for the prevention of tooth decay It also evaluates the effects of fluoride in water on the white or brown marks on the tooth enamel that can be caused by too much fluoride (dental fluorosis).
This marks the most comprehensive literature review to date on the subject, and instead of crystallizing our grasp on the effectiveness of community fluoridation programs, it has raised more questions than it answered. In this brief and admittedly superficial overview (cut me some slack; I had to work under a tight deadline while traveling!), I will attempt to unpack what the Cochrane Report says and means and, perhaps more importantly, what it doesn’t say and mean.
First things first: let’s look at the design of the systematic review. The consortium of Cochrane reviewers, possibly cloistered in a concrete bunker far beneath the Urals, searched through all of the major databases – The Cochrane Oral Health Group’s Trials Register, The Cochrane Central Register of Controlled Trials, MEDLINE via OVID, EMBASE via OVID, Proquest, Web of Science Conference Proceedings, and ZETOC Conference Proceedings . They searched the US National Institutes of Health Trials Registry (ClinicalTrials.gov) and the World Health Organization’s WHO International Clinical Trials Registry Platform for ongoing trials. From these sources, they found 4,677 references after eliminating duplicate search query results. For their inclusion criteria for tooth decay rates (also called dental caries), they included only prospective studies with a concurrent control that compared at least two populations – one receiving fluoridated water and the other non-fluoridated water – with outcome(s) evaluated at least twice, at separate times. For the assessment of fluorosis, they included any type of study design, with concurrent control, that compared populations exposed to different water fluoride concentrations. After applying these criteria to the large initial group of research literature, they winnowed it down to 155 papers that were suitable for evaluation. Twenty studies examined tooth decay, most of which (71%) were conducted prior to 1975. A further 135 studies examined dental fluorosis. Overall, it was a well-done, rigorous systematic review.
Let’s look at the results and conclusions, shall we? We’ll start with the fluorosis arm of the study, since it’s the easiest and most straight-forward. The researchers calculated that, in areas with a fluoride level of 0.7 ppm in the water (which is the current recommended concentration of community fluoride programs in the US), approximately 12% of the people evaluated had fluorosis that could cause concern about their appearance. And although the majority of the research articles (135 out of 155) were about fluorosis, the Cochrane Group still concluded that:
…(t)here 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.
So, for this part of the report, there is no real earth shattering news. At the recommended doses of fluoride, there is a small risk of fluorosis, harmless but potentially annoying cosmetically. We knew this already, and no new light was shed on the subject. However, what is of note here is that of the 135 studies – the best, most rigorous studies, mind you – the evidence was generally found to be not of high qualitative value. In fact, the authors stated “(o)ver 97% of the studies were at high risk of bias and there was substantial between-study variation.” Does that mean the research is wrong? No, it doesn’t, and the research probably isn’t wrong. The report merely speaks to the confidence one has in using said research for drawing any sort of definitive conclusions or making recommendations based upon it. It also speaks to what we Science Based Dentists have been screaming for years – that the quality and quantity of dental research at the population level is woefully thin and inadequate in many areas.
Which brings us to fluoride and dental caries. Here things get a little murkier, and the stakes are higher. After all, the entire raison d’être for the recommendation of fluoride by just about every dental, medical, governmental, and public health organization is to prevent cavities, the number one disease affecting the human species. If fluoride is shown to offer no protection against tooth decay, then its use cannot be justified, no matter how insignificant any side effect might be.
For this arm of the review, only twenty studies out of the original 4,677 search hits fit the criteria for evaluating the role of fluoridation and caries prevention. These studies too showed a high risk of bias, and even more problematic was that most of the studies included in the systematic review were done prior to 1975, before fluoride was used routinely in toothpastes, mouthwashes, and even topically in dental offices. At that time the city water supply was the primary source of fluoride. But since the pre-1975 studies and the post-1975 studies were merged into one meta-analysis, the confounding factor of fluoride sources other than municipal water obfuscate the significance of the results. Overall, community water fluoridation has resulted over time in a 35% reduction in tooth decay in primary teeth and a 26% reduction in permanent teeth. Moreover, fluoridation increased the percentage of children with no decay by 15%. These are very impressive numbers and attest to the vast reduction in pain, suffering, and dental health care expenses over every demographic group in society. That is why the Centers for Disease Control (CDC) has called fluoridation one of the Top Ten public health victories of the twentieth century.
But here’s the rub. Historically, it was thought that the benefits of fluoride occurred primarily via systemic ingestion, where it would be incorporated into the tooth enamel as it formed. Unfortunately, that is also the route by which fluorosis forms – a spanner in the works during tooth development. More recent research, however, has demonstrated that much (if not most) of the strengthening of the enamel is due to the topical effects of fluoride. Fluoride from toothpastes, fluoride varnishes, mouthwashes, and yes, even drinking water, “soaks” into the outer layers of enamel to make it more acid resistant and therefore less susceptible to dental caries. I hope that by now you can see why this systematic review is problematic in ascertaining if community water fluoridation programs are justified. Are the benefits we enjoy from fluoride primarily from toothpastes, professional dental applications, processed foods made with fluoridated water, or fluoride from community water supplies?
Despite the new report, fluoridation is still unanimously supported and endorsed by all of the major health organizations – the American Dental Association, American Academy of Pediatrics, American Association of Public Health Dentistry, the World Health Organization, the CDC, and so on. And while the pure benefits of water fluoridation aren’t as obvious due to widespread fluoride consumption by various other means, they are still important. For example, people living below the poverty line may not have access to good-quality fluoride toothpaste or professional dental fluoride varnish applications. Fluoridated water is a cheap and effective means to administer fluoride, and is non-discriminatory. Unfortunately, this too could not be substantiated in their report.
Ambiguity and qualifications
When you read the conclusions of the systematic review, the wording is much more ambiguous and non-committal in their endorsement of water fluoridation. To wit:
Although these results indicate that water fluoridation is effective at reducing levels of tooth decay in children’s baby and permanent teeth, the applicability of the results to current lifestyles is unclear because the majority of the studies were conducted before fluoride toothpastes and the other preventative measures were widely used in many communities around the world.
There was insufficient information available to find out whether the introduction of a water fluoridation programme changed existing differences in tooth decay across socioeconomic groups.
There was insufficient information available to understand the effect of stopping water fluoridation programmes on tooth decay.
No studies met the review’s inclusion criteria that investigated the effectiveness of water fluoridation for preventing tooth decay in adults, rather than children.
They sure said “insufficient information” a lot, didn’t they? If you weren’t a regular reader of Science-Based Medicine, you might read the report and conclude that the fluoride ship has sailed, that there is no longer a justification for putting fluoride in municipal water supplies. But since you are a regular reader, I’m certain the phrase “absence of evidence is NOT evidence of absence” immediately popped into your head. And that, dear reader, is (in my opinion) the crux of the review. Although it can be (and already has been) spun by the anti-fluoride crowd as evidence that fluoride isn’t effective, that’s not what the report says at all. Fluoride has a proven track record in the reduction of tooth decay. The main unanswered question (which the Cochrane Group hoped would be answered in this meta-analysis) is: to what degree of protection against dental caries does community water fluoridation currently confer? I think it can be assumed that if pre-1975 research papers were eliminated from the systematic review, and more recent high quality studies were available, the overall reduction in decay would be less than the pre-1975 levels. The authors state:
Our confidence in the size of effect shown for the prevention of tooth decay is limited due to the high risk of bias in the included studies and the fact that most of the studies were conducted before the use of fluoride toothpaste became widespread.
It’s this statement of limited confidence that has not only allowed the anti-fluoriders to seize upon it for their own aims, it has even led mainstream new sources to report on the report in such a way to mislead their readers. Newsweek’s headline, for example, reads “Fluoridation May Not Prevent Cavities, Scientific Review Shows“. Of course, this is irresponsible journalism, as that’s not what the review showed at all. But it does peddle false scientific information to its huge readership, which is regrettable for a news outlet of Newsweek’s caliber.
So until further research is in, you don’t have to attend anti-fluoride rallies or write a letter to your local newspaper calling for the cessation of community water fluoridation. It is still safe and effective, one of the best prevention values in health care. Each dollar that is spent on fluoridation reduces dental costs many fold, not to mention untold pain, suffering, loss of teeth, and loss of productivity.