Fluoride toxicity

A bit of a storm arose at Scienceblogs the other day when a blogger normally dealing with climate change allowed his father, James Beck, to do a guest post about a new anti-fluoridation book he had co-authored. Needless to say there were strong reactions on either side of the issue, including a response at Respectful Insolence. Since I’d been planning for a while to post something about fluoridation and just hadn’t got around to it, now seems like a good time.

Some of the arguments against fluoridation involve questions about how effective it is – I’m not going to get into that here (though in general the anti-fluoridation sites I’ve looked at use some pretty questionable analyses when downplaying its effectiveness). I’m also not going to get into the ethical side –  whether it is right for the government to administer fluoride in drinking water when some of the water users may not want it (though to me it’s not that much different than fortifying milk with vitamin D, enriching flour, etc.). I’m going to focus instead on my own area of expertise, specifically whether fluoride is toxic at the concentrations in drinking water.

First off, it’s important to remember that fluoride occurs naturally in water at a wide range of concentrations. In some places the fluoride is actually naturally higher than desirable and is treated to reduce the concentration.

The original post by James Beck made the following claims about fluoride:

  • Fluoride intake is a cause of impaired thyroid function. Indeed fluoride was once used medically to suppress thyroid function.
  • Deleterious effects on reproductive systems in humans have been found to be associated with fluoridation: in girls, early onset of menstruation; in men, low sperm counts.
  • We now have strong evidence of the association of osteosarcoma in boys and young adult males with fluoridation. Osteosarcoma is a bone cancer which is often fatal.
  • The possible incidence of bone fracture with fluoridation has been studied with mixed results. One of the strongest studies is presented in a paper by Li et al. published in 2001 which shows a rising prevalence of hip fracture correlated with a rising intake of fluoride starting with concentrations comparable with those used in fluoridation in North America. And this is just one example that suggests that hip fracture is caused by fluoridated water.
  • Fluoride adversely affects kidneys.
  • Two recent studies have shown adverse effects on the heart and the aorta.

There are some strong claims here – unfortunately not much linking it to actual concentrations or doses and no references. Dr. Beck later provided a link to the bibliography to his book in the comments, though it still isn’t easy to track down the references for the specific effects, and only a few of the references are to original studies in reputable scientific journals. I imagine the references are more traceable in the book, but I don’t have a copy of it (and probably don’t have enough readers to warrant getting a free copy from the publisher, even if I did have time to read it). However, the effects claimed are based on available scientific literature which is readily available, along with reviews by major health agencies.

Bone Toxicity

I’m going to start with bone toxicity, since fluoride in the body resides primarily in the bone, and it has been shown to affect bone density. Some studies have suggested a biphasic effect on bone strength and fractures, with low doses increasing bone strength and higher doses resulting in a decrease. The paper by Li et al. (2001) referenced by Dr. Beck, which looked at fracture rates in different villages in China, actually shows some indication of this effect, with the lowest rate of overall fractures appearing in communities with fluoride levels around 1 ppm. For hip fractures, the rate was pretty constant at concentrations around 1 ppm and lower, and showed an increase at higher concentrations. The relevant graphs from the paper are below:

Based on these data, concentrations higher than 1 ppm in drinking water appear to be associated with some increased risk of fractures (while the increase isn’t statistically significant until the highest dose, the overall dose-response trend can’t be ignored either). Several other similar studies have been conducted, and included in reviews by agencies such as NRC and Health Canada; results have been fairly mixed, and most of these studies have some fairly significant limitations and confounding factors. However, overall it appears that high fluoride concentrations in water are associated with increased rates of hip fractures in particular, but these effects generally occur above 1 ppm.

Bone Cancer

Several studies have looked at the relationship between fluoride and osteosarcoma (a cancer of the bone), again with mixed results. Perhaps most notably an exploratory epidemiological study by Bassin et al. (2006) found some indication of a relationship between fluoride exposure and osteosarcoma in males, but not females. However, exploratory studies are notorious for false positives, and require follow-up to confirm their conclusions; even the authors of this study cautioned against reading too much into the results. Analysis of an expanded data set, using the same hospitals, the same pathology departments and similar methods of fluoride exposure estimation did not find any association between fluoride and osteosarcoma. A recent expert panel convened by Health Canada to study the issue concluded the current weight of scientific evidence does not support an association between fluoride and cancer.

Other Effects

As Dr. Beck noted, high fluoride exposures have been associated with other effects such as thyroid effects and kidney stones, but these effects were generally observed at concentrations on the order of 4 ppm. Some studies have shown evidence of reproductive effects, but have had issues such as poor control of confounding factors, and again involved high fluoride concentrations. Available studies have been summarized in the recent reviews by NRC and Health Canada.


Overall the data do not appear to show evidence of significant adverse effects (other than fluorosis) at the “target” concentration in drinking water of approximately 1 ppm. Higher concentrations, particularly in the range of 4 ppm and above, do appear to be associated with a variety of adverse effects and should be avoided – areas where fluoride naturally exceeds this concentration should use appropriate treatment to reduce the concentration. There are certainly limitations to the existing data; in particular, the epidemiological studies on which the conclusions are based would likely only detect population-level effects, and may not detect rare effects in very sensitive individuals. While based on the mechanisms of toxicity and pharmacokinetics of fluoride I wouldn’t necessarily expect huge differences in response between different individuals (at least compared to a lot of organic chemicals), further study is worthwhile. There is also some concern about exposure from sources other than drinking water, which can be significant at concentrations of 1 ppm; generally the better-designed studies have incorporated this, but many of the foreign studies may involve populations with different exposures to fluoride from sources other than water than typical North American populations.

18 Responses to Fluoride toxicity

  1. coby says:

    Hi Ash,

    Thanks for taking the time to have a serious look.

    Just to play devils advocate here, I would be interested in your assessment of the validity of an argument that proceeds as follows:

    – toxicity has been demonstrated at average dosage levels X delivered via fluoride concentrations of level Y
    – dosage levels of level X can and do in fact occur in some sub-groups of a population exposed to fluoride concentrations Z
    – therefore it is inadvisable to administer fluoride at a concentration of Z based on the study dealing with concentrations of Y

    Obviously the study is Li et al, X would be some number of mg/day of fluoride, Y is 3 or 4ppm and Z is 1ppm.

    I am speculating that this is how it is presented in the book.

    PS. Did you read the very unflattering things “Kieran” had to say about Li et al methodology? Criticisms that would cover most such studies.

  2. Everett Williams says:

    What is left out here is the amount of disease and death caused by caries prevented by fluoride as opposed to the largely anecdotal accounts of death or disease caused by “normal” levels of fluoride, which, according to standards, should range from 0.7 to 1.2 depending on average temperature and local occurrence of fluoride. Much like his screeds on CO2 and climate, Beck’s writings are acceptable where they stick to citations of the historical record, but completely baseless when taken to conclusions. Mr. Beck does no original research, and his statistical and analytical chops are more than a bit questionable. It’s always interesting to cite records of CO2 concentration taken in the 1830’s during the heyday of homeopathy as dependable. We did not even have reliable standard measures at that point in time, especially when we are talking about parts per million. To my knowledge, no one has attempted to replicate the methodology used by his various reporters through time, and it is doubtful that there is sufficient information to do so. Given that level of uncertainty, it is hard to give a lot of weight to his arguments.

    But let us go back to fluoride. With fairly good data on advantages and no reliable data on harm, there is little that should be argued here until solid data of harm is provided.

  3. nyscof says:

    I think you miss the point and get way too complicated on a simple problem. Show us that fluoridation of water supplies is safe and effective. Look at that science. Is it valid?

    If your government won’t fund studies looking at adverse health effects due to fluoridation, does that mean fluoride is harmful to no one? The average person can make a logical conclusion based on the existing data especially since ingesting fluoride does not reduce tooth decay.

  4. coby says:

    Oh dear. I must make something very clear. There are three different Becks here. Ernst Beck is the one with the CO2 measurements wildly at odds with ice cores and physical constraints of the carbon cycle. Coby Beck (me) is the proprieter of the blog A Few Things Ill Considered. James Beck wrote the guest post Ash is examining here and co-authored The Case Against Fluoride. James is my father, Ernst is no relation.

    One more! Glenn Beck is also no relation whatsoever!

  5. ashartus says:

    Hi Coby. Regarding concentrations vs. doses, there is some validity to that point. Many of the studies do actually attempt to estimated doses and use those in their analyses; I presented everything in terms of concentration to keep things relatively simple for a blog post aimed at a more general audience. There’s a lot of uncertainty in estimating doses from most of the available studies though; you generally don’t know exactly how much water each individual is drinking and what other exposures they might have (if fluoride concentrations in water are 4 ppm the other exposures don’t matter much, but if concentrations are 1 ppm or lower they start to become noticeable).

    The 2008 Health Canada evaluation actually did come up with a tolerable daily intake (basically an estimated safe dose) from the available data and used that along with normal water ingestion rates to include that a fluoride concentration of 1.5 ppm was not expected to pose a risk.

    I do agree there are limitations in that some individuals may consume higher amounts of water than normal and also have higher exposures from other sources, and so might have a higher exposure dose than is normal for a particular concentration in water. From what I’ve read I think it would be fairly unlikely for someone drinking water at 1 ppm to have the equivalent exposure to a normal person drinking water with 4 ppm though, unless they had some really unusual source of high fluoride exposure. If you consider 1.5 ppm (for example) to be the maximum safe concentration for a normal consumer though, it might be a different story.

    Another limitation which I briefly mentioned is that most of the studies conducted could only detect population-level effects, so if there are rare individuals with high exposure and/or high sensitivity the effects on these individuals might not be detected.

    Overall I don’t think it’s a completely black and white issue. If the margin of safety were a bit higher it would be pretty clear-cut, but when the margin of safety is a factor of 3 or 4 that’s a bit lower than ideal. In those cases you have to look at the overall benefit to the population vs. the risk. With that sort of margin of safety I also think continued research and regular re-evaluation is important. While I don’t agree with Dr. Beck and his co-authors on some of their points, I can accept that there are valid concerns. I probably at this time fall into a mildly pro-fluoride position, but not without some reservations.

    As far as the criticism of the Li et al. study goes, those are probably valid points. The commenter seems to have a much stronger stats background than me, but the criticisms seem to make sense. Some of the flaws may not affect the overall conclusions though. My biggest concerns would be how similar the villages are to each other, and how relevant the population in villages in China is for North American populations. Generally the regulatory agency reviews found all of the studies to be fairly flawed though.

  6. ashartus says:

    Everett – I agree you have to consider the beneficial effects too. I deliberately limited my discussion to one side of the benefit vs. risk equation, since my experience is more with the bad things chemicals do to you than the good things. But when determining whether or not fluoride should be added to drinking water, you need to look at both sides. Agencies like Health Canada and CDC have done this, and concluded that the benefits outweigh the risks. Having been involved in some Health Canada chemical evaluations, I’m fairly comfortable that the process they use is reasonable, and when my own (relatively brief) review doesn’t find any critical flaws in their evaluation I’m inclined to believe them.

  7. ashartus says:

    Nyscof – the whole point of the evaluations undertaken by agencies like Health Canada, CDC, etc. is to determine whether fluoridation is safe and effective. They have concluded that it is, based on the existing data (and that the data do show it is effective in reducing tooth decay). There is ongoing research, and given the reservations I have discussed above I fully support further research to make sure the position is valid.

  8. nyscof says:

    Ashartus – My point is that it’s good to evaluate science; but look at the science from both sides if one truly wants to find the truth. The Centers for Disease Control does not do any original research according to testimony by the chief fluoridationist and dentist who works in the oral health section of the U.S. Centers for Disease Control. He listed, to the Fairbanks Alaska City Council, the studies and reports which proved fluoridation is safe and effective. The trouble is that most of the studies and reports he mentioned do not prove fluoridation safety or efficacy – some even prove the opposite. See: http://forum.starnewsonline.com/viewtopic.php?f=5&t=1949

    My opinion is that the CDC’s oral health section is hired to promote fluoridation – not study it.

    So if you blindly trust government agencies, then there’s really no reason to make believe you are actually critically and objectively reviewing research showing fluoride’s harmful effects.

    Further, future studies are hampered by lack of funding to carry out such research. One would have thought such research was carried out before fluoridation began in the 1940’s but it wasn’t.

    So here we all sit as guinea pigs in this ongoing fluoridation experiment.

    It’s simple: Early researchers thought ingesting fluoride reduced tooth decay. Modern science shows it doesn’t. Time to stop fluoridation.

  9. nyscof says:

    An interesting story emerged in the Washington Post highlighting how CDC and EPA can’t be trusted (It’s about lead – not fluoridation.

    Debacle over drinking water deals a blow to CDC and EPA

    By Robert McCartney
    Washington Post Staff Writer
    Sunday, December 5, 2010

  10. Everett Williams says:

    Unless this is to become a general paranoia about government column, we need to stick to specifics. The cited Chinese study completely ignores the insularity of Chinese village life, where interrelatedness can strongly influence such factors as intelligence, and locality and customs and diet can provide other influences on intelligence, all very difficult to isolate, and all needing a much more representative and distributed population to be more than anecdotal. Considering the number of populations with and without fluoried, including ones with no fluoride and others with more than recommended amounts, that are available in the U.S., the only thing holding them back is will and funding.

    I would say that the reason that such funding isn’t generally forthcoming is that the scientific community sees it as a very low priority, considering the number of them that have been raised with tons of fluoride from a variety of sources, not to mention the amount of reasonably useful research that has already been done.

    Since the Chinese study shows general and clear effects at a dosage well below the generally tested and accepted level of 4.0, I would be taking a very close look at something that seems so definitive.

    By the way, sorry about the confusion of Becks. Now, if the paranoid conversation persists, we may want to reexamine the relationship to Glenn.

  11. […] been claimed for fluoridation of drinking water that I didn’t really examine in my previous examination of fluoride toxicity is reduced IQ. The major regulatory reviews have previously concluded there is no evidence for any […]

    • Paul says:

      Hi Coby,
      having studied the fluoridation issue for years now, I have 197 studies that show the mechanisms, as to how the human body is damaged by fluoride. The studies that show benefit, I cannot access, I have even challenged my dentist to supply one ! The issues of whose studies are more reliable, pro or con, become irrelevant for many reasons.
      One- The manufacturers themselves on the MSDS sheets provide the real data. It is clearly stated the Hydrofluosilicic acid, which is what they put in our water, has never been tested for human consumption.
      Secondly, since 95 to 98% of the fluoridated water is used to wash things and flush, all that fluoride compound is ending up in our rivers. Which is exactly what the Ministry of the Environment said the Aluminum plants and Organophosphate Plants are not allowed to do. The found a way to dilute the poison in our water systems and our kidneys.
      The rest of the evidence is right before our own eyes…. the toothpaste tubes all say do not swallow ! So what do we really need more before we exercise caution . Stop it for our children’s sake. Paul

  12. ashartus says:

    Paul, there are several flaws in your reasoning:
    – There are plenty of studies showing benefits of fluoride<
    – Hydrofluorosilic acid does not stay in that form after being added to water.
    – No one disputes that high doses of fluoride can cause harm (just like high doses of anything else). What is disputed is that the concentrations in drinking water systems, which are equivalent to the control or low exposure groups in the studies that anti-fluoridation groups quote, are harmful. Many places naturally have higher fluoride concentrations than that – water fluoridation is more about controlling concentrations at an optimum amount than anything else.

    The argument that most of the fluoridated water is not used for drinking is a more reasonable argument (and not really the subject of this post). To use it to justify stopping fluoridation, you'd still need to demonstrate that the economics of delivering fluoride this way vs. other approaches don't make sense, or that these concentrations (which are well within the range of naturally occurring concentrations) are harmful to the environment.

  13. I’m aware this is ancient at this point, but I came across this debate tonight as part of a search and one thing really struck me as being missed in all the skeptical commentary both on the two scienceblogs involved and here on the exposure/effect blog:

    If James Beck and Paul Connett are, in fact, scientists who have extensively studied the issue of fluoridation for the past 14 years, why did they make their case against the scientific consensus in a book marketed to the general public rather than as a scientific research paper in an appropriate peer-reviewed publication? Is that not itself a strong sign of crankdom?

  14. coby says:

    Hi Jarandhel,

    I will suggest an answer to your question, if I may put possible words into J. Beck’s and P. Connett’s mouths: they are advocating for policy based on existing science. Presumably, they feel that the research already exists to support their position, it is time to change public policy not study it some more.

    Putting aside the correctness of that position, it does seem reasonable.


    (BTW. I will clear your identical comment through moderation on A Few Things Illconsidered and provide the same reply in the near future after it would have fallen off the recent comments list. I have no desire for that issue to flare up on my blog again!)

    • Colby, would you accept that answer from any scientist who is not your own father? If you were told that climate-change skeptics were making their case in the court of public opinion rather than scientific journals because they believed the science was already settled on their side — despite the scientific consensus being the exact opposite of their conclusion — what would your response be?

      • coby says:

        My response would be to assert that they are very wrong and I think it would be pretty straightforward to refute each and every point they might claim with existing and well established research.

        The correct place for policy advocacy is the court of public opinion. It is appropriate for Richard Lindzen or James Hansen to write op-eds in newspapers trying to convince the public of their preferred policy direction. What is inappropriate is dishonesty and misrepresentation of the facts of the matter at hand, what we see in Lindzen’s writings.

        If Richard Lindzen wants to establish a specific scientific point such as climate sensitivity is much lower than the current climate models all exhibit, this definitely should be done in a scientific journal and is not appropriate for writings targeted at a lay-audience.

        I think those principals are reasonable, and I hope we could agree on them. I will readily concede that grey areas and subjective circumstance make applying them controversial and we would need to be more specific if you want to establish a violation of them.

        Do you see anything specific that might fail the above standards?

      • ashartus says:

        Wow, actual discussion on this blog despite it being inactive for around 2.5 years (due to my extreme lack of time). In general I think you both have good points. To some extent I think there is a place for policy advocacy in the court of public opinion, though the downside of that is that sometimes the public can be swayed by faulty science and misrepresentation of facts such as we see in climate change debates. In the case of fluoridation, I think there are valid arguments for both sides. Unfortunately a lot of the debate gets influenced by the faulty science. The issue I have with Beck et al. is that at least some of the arguments are based on things like misinterpretation of studies (e.g. studies that showed an effect of high fluoride exposures, but the low-dose control group had higher fluoride concentrations than North American fluoridated water supplies). If instead the argument was framed not on adverse effects but instead the debate on effectiveness or whether it makes economic sense I’d have no problem with their position whether I agree with it or not (I realize they do include these arguments as well – it’s just that they also include arguments based on what I consider to be faulty science).

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