Study uses mathematical models to examine link between water fluoridation and diabetes

Water fluoridation prevents dental cavities, which are a costly public health concern. But despite the benefits supplemental water fluoridation remains a controversial subject. Some indicate it may cause long term health problems, but studies reporting side effects have been minimal or inconclusive. The long-term effects of ingested fluoride remain unclear.

A recent study published in the Journal of Water and Health examined links between water fluoridation and diabetes. Type 2 diabetes is a growing epidemic in the United States. Incidence rates have nearly quadrupled in the past 32 years and show no signs of stopping. According to the study, fluoridation with sodium fluoride could be a contributing factor to diabetes rates in the United States, as the chemical is a known preservative of blood glucose.

The sole author of the paper, Kyle Fluegge, PhD, performed the study as a post-doctoral fellow in the Department of Epidemiology and Biostatistics at Case Western Reserve University School of Medicine. Fluegge now serves as health economist in the Division of Disease Control for the New York City Department of Health and Mental Hygiene and co-director of the Institute of Health and Environmental Research in Cleveland, Ohio.

In the study, Fluegge used mathematical models to analyze publicly available data on fluoride water levels and diabetes incidence and prevalence rates across 22 states. He also included adjustments for obesity and physical inactivity collected from national telephone surveys to help rule out confounding factors. Two sets of regression analyses suggested that supplemental water fluoridation was significantly associated with increases in diabetes between 2005 and 2010.

"The models look at the outcomes of [diabetes] incidence and prevalence being predicted by both natural and added fluoride," said Fluegge.

Fluegge reported that a one milligram increase in average county fluoride levels predicted a 0.17% increase in age-adjusted diabetes prevalence. Digging deeper revealed differences between the types of fluoride additives used by each region. The additives linked to diabetes in the analyses included sodium fluoride and sodium fluorosilicate. Fluorosilicic acid seemed to have an opposing effect and was associated with decreases in diabetes incidence and prevalence. Counties that relied on naturally occurring fluoride in their water and did not supplement with fluoride additives also had lower diabetes rates.

The positive association between fluoridation and diabetes was discovered when Fluegge adjusted fluoride exposure levels to account for estimated per capita tap water consumption.

"The models present an interesting conclusion that the association of water fluoridation to diabetes outcomes depends on the adjusted per capita consumption of tap water," explained Fluegge. "Only using the concentration [of added fluoride] does not produce a similarly robust, consistent association." For this reason, Fluegge adjusted his calculations to incorporate tap water consumption, instead of sticking to calculations that rely on "parts per million" measurements of fluoride in the water.

Fluegge used several estimations in his study, including calculations of county-level water fluoride levels; per capita county tap water consumption; and county measures of poverty, obesity and physical inactivity. Although he doesn't suggest the study should trigger policy changes, he does indicate it should serve as a call for additional research on the important association between fluoridation and diabetes.

"This is an ecological study. This means it is not appropriate to apply these findings directly to individuals," explained Fluegge. "These are population-level associations being made in the context of an exploratory inquiry. And water is not the only direct source of fluoride; there are many other food sources produced with fluoridated water."

In addition to being found in food like processed beverages or produce exposed to specific pesticides, fluoride is found naturally in water in the form of calcium fluoride. Supplemental fluoride was first added to community water supplies in the 1940s.

Said Fluegge, "The models indicate that natural environmental fluoride has a protective effect from diabetes. Unfortunately, natural fluoride is not universally present in the water supply."

Residents can learn more about fluoride levels in their communities through the Centers for Disease Control My Water's Fluoride database.

Source: Case Western Reserve University


  1. Janet Nagel Janet Nagel United States says:

    The introductory statement that fluoridation prevents dental caveties is gratuitous and scientifically false. Tooth decay rates in fluoridated and non-fluoridated localities are the same. The CDC admits that fluoride acts on tooth surfaces to prevent decay. Ingested fluoride has no beneficial effect.  Ingesting it is like swallowing suntan lotion to prevent sunburn. If you're going to claim to be medical news you really need to get up to speed.

    • Steven Slott Steven Slott United States says:

      Janet, as usual, there is not a grain of truth in your comment.  

      1.  Countless peer-reviewed scientific studies clearly demonstrate the effectiveness of fluoridation.

      2.  Attempting to assess one preventive measure, fluoridation,  based on snapshots of data from different countries, controlling for none of the numerous variables involved in dental decay is, obviously, ludicrous.

      3.  The CDC has not "admitted" anything.  It has duly reported the scientific evidence showing that the effect of fluoride is both topical and systemic....and made its recommendations accordingly.

      4.  If suntan lotion has been demonstrated by peer-reviewed science to prevent sunburn systemically, while causing no adverse effects, your analogy might make some semblance of sense.  Otherwise it is as ridiculous as the rest of your unsubstantiated nonsense.

      Steven D. Slott, DDS

  2. Steven Slott Steven Slott United States says:

    Aside from the obvious inadequacy of controls for the numerous confounders involved in diabetes, this study makes false claims  which render it completely void of  credibility.

    1.  Fluoride is the anion of the element fluorine.  An anion is a negatively charged atom.  One such atom of fluorine is identical to all other such atoms of fluorine.  There is no difference between "naturally occurring" atoms of fluorine and those added through fluoridation.

    2.  Calcium fluoride is not a "form of fluoride".  It is a compound that contains fluoride. An atom is not a compound.  Calcium fluoride is therefore not "natural fluoride", nor does it even exist in groundwater.  As this water flows over rocks it picks up fluoride ions leached from calcium fluoride and fluorosilicates in those rocks.  It is  these fluoride ions, not the compound calcium fluoride,  which are to what is commonly referred as being "naturally occurring" fluoride.

    3.  Fluorosilicates are immediately and completely hydrolyzed upon addition to drinking water.    After that point they no longer exist in that water.  They do not reach the tap.  They are therefore not ingested.  The product of this hydrolysis is fluoride ions, identical to those "natural" fluoride ions already existing in water.   As such, there is no difference between "natural" fluoride, and that added through fluoridation.  Additionally, as fluorosilicates are not ingested, it is not possible for them to have any effect on incidence or prevalence of diabetes.

    Given the false claims put forth in this "study" it can be clearly seen that the study has no credibility whatsoever.

    Steven D. Slott, DDS

  3. Dan Germouse Dan Germouse Australia says:

    I have asked many forced-fluoridation fanatics to tell me how much accumulated fluoride in the body they think is safe. So far not a single one of them has been able to answer the question.

    It is unlikely to just be a coincidence that the US, Australia, and Ireland, which have had high rates of forced-fluoridation for decades, also have high rates of joint problems, and poor health outcomes in general.

    • Steven Slott Steven Slott United States says:


      1.  Your "question" has been answered so many times that I've long since lost count.  The fact that you don't understand the answer is a problem with you, not with fluoridation.

      2.  What you deem to be "unlikely" is of no relevance.  If you have any valid, peer-reviewed scientific evidence that optimally fluoridated water is associated with "high rates of joint problems, and poor health outcomes in general", then present it, properly cited.  As no such evidence exists, this will be difficult for you to accomplish.

      Steven D. Slott, DDS

    • David Fierstien David Fierstien United States says:

      And I asked many anti-fluoride fanatics to name one single person who has ever been harmed by drinking optimally fluoridated water . . even for as much as a lifetime - with documentation of course.  So far, not a single one of them has been able to answer the question, including Dan gerMouse here.

  4. Dan Germouse Dan Germouse Australia says:

    There is no credible evidence that fluoridated water has ever prevented a single dental cavity. The forced-fluoridation fanatics often try to claim that the low rates of dental caries in western European countries which do not have artificially fluoridated public water supplies are due to naturally occurring fluoride in water, or some other kind of artificial fluoridation such as salt fluoridation. They are lying. They also rely on studies which do not measure individual fluoride exposure, are not randomised, are not blinded, do not properly account for confounding factors, are highly prone to systematic error, and are typically funded by corporations such as Colgate-Palmolive.

    • Steven Slott Steven Slott United States says:


      1.  There are countless peer-reviewed studies which clearly demonstrate the effectiveness of fluoridation in the prevention of dental decay in entire populations. Numerous such studies have been cited for you previously in an effort to properly educate you on this issue.  I will gladly do so again if you wish.

      2.  If you have proof that those who report accurate information on dental decay rates in Europe are "lying", then produce it.  Otherwise it is obvious whom is the one lying here.

      3.  Randomised controlled trials are not feasible for large population based public health initiatives, such as fluoridation, and will never be performed for this initiative.  The recent Cochrane Review understood this and noted it in it its report.  It is a mystery as to why you seem so confused with this.  The data from cross-sectional, observational studies on fluoridation are perfectly acceptable within respected science and healthcare as accurate assessments of this initiative.

      "However, there has been much debate around the appropriateness of GRADE
      when applied to public health interventions, particularly for research questions where evidence from randomised controlled trials is never going to be available due to the unfeasibility of conducting such trials. Community water fluoridation is one such area."

      ---Water fluoridation for the prevention of dental caries (Review) 28
      Copyright © 2015 The Cochrane Collaboration

      3. Your personal opinion on the quality or validity of peer-reviewed scientific literature is irrelevant.  You have no qualifications to render any credible assessment of such literature.

      Steven D. Slott, DDS

  5. Billy Budd Billy Budd United States says:

    This news coverage appears to completely miss the primary point of the study's findings.   Hexafluorosilicic acid, the overwhelmingly most common fluoride water additive was found to protect against diabetes.  

    Quoting:  "Among the three used in this data set, fluorosilicic acid was most significantly associated with reduced diabetes incidence (β ¼ –0.45, P< 0.001), inducing the greatest decline in incidence apart from the year variable."

    So the study's mathematical model found the most common additive affords protection from diabetes with a statistical uncertainty of under 1 in a 1,000.  

    From the perspective of an oral health advocate, I'm not upset if a water district chooses the more common, less expensive water additive rather than sodium fluoride. . just fine with me.

The opinions expressed here are the views of the writer and do not necessarily reflect the views and opinions of News Medical.
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