Water fluoridation benefits and risks – a systematic review

Water fluoridation has become a fairly common public health practice, as communities across the world accepted the evidence that fluoridated water is relatively safe and reduces cavities (known properly as dental caries). Several decades ago, it became a part of the public health strategy in many communities.

However, as fluoride became more available, especially in the forms in toothpaste and various mouthwashes, it has become time to review water fluoridation benefits and risks – especially as it becomes one of those “things” that cause concerns with the public.

As I’ve mentioned literally a few hundred times in this blog, the very highest level of research is a meta (or systematic) review, which tries to identify, appraise, select and synthesize all high quality research evidence relevant to a particular question or hypothesis in medicine. Systematic reviews of high-quality randomized controlled trials are critical pieces of evidence that forms the basis of science-based healthcare.

Systematic reviews are best when they select hundreds or even thousands of research studies over decades of clinical studies, eliminating studies with bias (or pointing out the bias), and combining data from the best of the best. Now it’s time to look at one of the newer meta-reviews regarding water fluoridation benefits and risks from the Cochrane Collaboration, probably the premiere group that produce systematic reviews.

Using data from a wide variety of resources (from clinical trials to peer-reviewed studies to recommendations from public health organizations), the Cochrane Collaboration attempts to find the best and least biased data to answer a question. In case you’re wondering who is this “Cochrane,” they are either a group of brilliant scientists trying to provide better data for medicine or dentistry. Or they’re a cabal of evil wizards, hiding from the world in a dungeon in one of Big Pharma’s creepy castles in New Jersey. My guess it’s the former.

Why is fluoride so important for teeth?

 

Fluoride is the naturally occurring  inorganic anion of fluorine. It has one negative charge, and is found in fairly large quantities in the form of calcium fluorite (CaF2), the most common form of fluoride.

Fluoride has a very simple mechanistic effect on teeth (and dental caries). Fluoride operates on tooth surfaces by reducing the rate at which tooth enamel demineralizes and increases the rate at which it remineralizes in the early stages of dental caries. In other words, it reduces the damage to teeth from cavities, but it also can repair it, as long as it is done early enough.

Water fluoridation works by increasing, very slightly, the concentration of fluoride in the saliva, which constantly bathes the teeth in very low levels of fluoride. And by doing so, it reduces the risk of cavities, while also inducing some repair of the teeth. Please note that if a tooth has significant damage from a cavity, fluoride is probably not going to repair it. Fluoride is not something where a little helps, so a lot must help a lot.

The systematic review of fluoride.

 

In a June 2015 systematic review from Cochrane, the authors asked this question:

[infobox icon=”quote-left”]This review was conducted 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).[/infobox]

So, it’s actually more than one question, it’s several:

  1. Effect of artificial fluoridation (what we know as water fluoridation) for the prevention of dental caries.
  2. Effect of natural fluoridation (many water supplies have natural levels of fluoride, it’s a fairly common salt on earth).
  3. Effects of water fluoridation on dental fluorosis, a brownish stain on teeth–a common side-effect of fluoridation. It is not considered a health risk, being mostly a cosmetic issue.

Researchers from the Cochrane Oral Health Group, probably not hiding in the dungeons of Big Pharma, reviewed published evidence, through February 2015, for the effect of water fluoridation on those questions above. The researchers identified 155 studies (out of 4677 related papers) in which children receiving fluoridated water (either naturally occurring or artificially added to the water supply) were compared to those who received water with very low or near zero levels of fluoride.

Of those 155 studies, twenty examined tooth decay–most of which (71%) were conducted prior to 1975. The other 135 studies examined the effects of water fluoridation on dental fluorosis.

natures-way-cause-tooth-decay

What did the researchers find?

 

Fluoridation and cavities–It’s kind of telling that of the 4,677 papers originally analyzed, only 20 were good enough (or actually addressed the question presented) to be included in the systematic review. Furthermore, 14 of those papers were published prior to 1975. We don’t necessarily dismiss the quality of papers published 40 years ago, but there have been substantial changes in dental healthcare over that time.

Since 1975, fluoride has become a “standard” ingredient in toothpastes, mouthwashes, and other over-the-counter dental care products. In addition, regular dental check-ups routinely include fluoride in topical applications, such as teeth cleaning. Prior to 1975, the water supply was the primary source of fluoride, and since then, it might be in any of your Crest or Colgate toothpastes.

I do consider Cochrane to be one of the best systematic review groups in the world, but I do not believe they are perfect. In this case, the study should not have combined data from pre- and post-1975. There could be some confounding of the data before and after 1975. Furthermore, the researchers admit that there could be a high risk of bias in those 20 studies.

 
 
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Even the authors discussed the issues with these studies:

[infobox icon=”quote-left”]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.[/infobox]

That being said, the data is still fairly impressive, and constitutes fairly robust evidence that water fluoridation does reduce tooth decay in communities. The researchers found that:

  1. There has been a 35% reduction in dental caries in primary teeth (the first set of teeth in children).
  2. There as been a similar 26% reduction in cavities in permanent teeth (the final and second set of teeth).
  3. There has been an increase, by 15%, in the number of children who have had no dental caries.

Despite the issues with these 20 studies, those are dramatic improvements in the dental health of our children. This data confirms what the Centers for Disease Control and Prevention  (CDC) have long stated–water fluoridation is one of the greatest public health achievements, much like vaccinations.

Dental fluorosis–However, all medicine has some benefits and some risks. Those that claim that there’s not some sort of benefit to risk analysis are generally not speaking factually. For fluoridation, where the benefits require oral consumption of the fluoride also happens to lead to dental fluorosis. But fluorosis is not dangerous, and really is mostly a cosmetic issue.

According to the study, it was calculated that, “in areas with a fluoride level of 0.7 ppm in the water, approximately 12% of the people evaluated had fluorosis that could cause concern about their appearance.”

Setting aside the one small “risk” (which really isn’t a health risk), what do we know? The evidence does show us that fluoridation is highly beneficial to preventing dental caries. But we don’t know if water fluoridation is only a small part of the effect, or it has a substantial synergistic effect with other fluoride sources (toothpastes, mouthwashes, and other topical applications). Or something in between.

For example, we have no clue how community water fluoridation has differential effects in different economic groups. Those who are poor may not have access to dentists or better dental care, and water fluoridation may be the best (cheap and effective) method to deliver fluoride to a population. There might be areas within communities with cultural differences regarding dental health.

Summary, the TL;DR version

 

In case you think this study is damning by faint praise, remember water fluoridation is endorsed by nearly every public health organization in the world – American Dental AssociationAmerican Academy of PediatricsWorld Health Organization, and CDC. This is about as close to unanimous as you can get (and pretty close to a scientific consensus, to be honest). Yes, we need more information, but at this point, we do not lack evidence that fluoridation prevents dental caries–we need better evidence to fine tune our public health strategies for dental care.

However, even the authors of the study said that they needed more information:

[infobox icon=”quote-left”]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.[/infobox]

They did not conclude that water fluoridation was useless. In fact, they found quite the contrary. What the authors, and many of us interested in public health, want is better information to “fine tune” what we are doing.

However, as long as the health risks are minimal (or cosmetic), and the benefits have been shown over and over, this study provides no reason to stop water fluoridation. But what it does ask, how can we do it better? How can we make sure those who have little access to quality dental care be protected? Those are important questions. That’s how science based medicine works, continually asking question to get better data to improve health care.

Key citations:

 

The Original Skeptical Raptor
Chief Executive Officer at SkepticalRaptor

Lifetime lover of science, especially biomedical research. Spent years in academics, business development, research, and traveling the world shilling for Big Pharma. I love sports, mostly college basketball and football, hockey, and baseball. I enjoy great food and intelligent conversation. And a delicious morning coffee!