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Home » Scientific review of fluoride in water — benefits and risks

Scientific review of fluoride in water — benefits and risks

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 to add fluoride to water.

However, as fluoride became more available, especially in the forms of 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.

This article isn’t going to cherry-pick data to support one side or the other of the whole fluoridation debate, I’m going to use published peer-reviewed articles that are at the top of the hierarchy of medical research. So here we go!

close up photo of woman with pink lipstick smiling with her eyes closed water fluoride
Photo by Shiny Diamond on

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 (commonly known as cavities). Fluoride operates on tooth surfaces by reducing the rate at which tooth enamel demineralizes and increasing 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 with 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 water

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

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).

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 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.


What did the researchers find about fluoride in water?

Fluoridation and cavities — Since 1975, fluoride has become a “standard” ingredient in toothpaste, 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 toothpaste.

Even the authors discussed the issues with these studies:

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.

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

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

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 medical procedures have benefits that need to be compared to the risks. 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 in preventing dental caries. But we don’t know if water fluoridation is only a small part of the effect, or if 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 (inexpensive and effective) method to deliver fluoride to a population. There might be areas within communities with cultural differences regarding dental health.


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 clearly represents a scientific consensus on fluoride in water.

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 is, 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 questions to get better data to improve health care.

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Michael Simpson

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