2007 was yet another important year in fluoride research, with studies not only questioning long-held views about fluoride’s benefits, but raising new concerns about its impact on human health. To give an indication of this recent research, the Fluoride Action Network (FAN) has selected the “Top 10” scientific developments of the year. They are as follows:
1) New Evidence on Fluoride & the Developing Brain
In 2007, the question of how fluoride affects the developing brain gained renewed attention from researchers around the world. Research teams from Brazil, China, India, Italy, Mexico, and the United States conducted important new analyses, including 3 new studies investigating fluoride’s impact on childhood IQ (1a,b,c), and several new animal studies investigating fluoride’s effects on learning, memory, and behavior (1d,e). The studies, which strengthen the concerns expressed by the US National Research Council in 2006, further highlight that it’s not just the teeth, but the brain, that may be impacted by too much fluoride during infancy and childhood. As noted in a review presented this fall by Harvard scientists Philippe Grandjean and Anna Choi:
“In humans, only five substances have so far been documented as developmental neurotoxicants: lead, methylmercury, polychlorinated biphenyls, arsenic, and toluene. From this evidence, including our own studies on some of these substances, parallels may be drawn that suggest that fluoride could well belong to the same class of toxicants, but uncertainties remain” (1f).
While uncertainties remain — as is common in science — several of the studies published this year made important advances in addressing some of the shortcomings of previous research. In particular, a study (1a) linking high-fluoride (5 ppm) water to reduced IQ among a group of Mexican children made important steps in the right direction by simultaneously controlling (via multiple regression analysis) for other key factors known to affect IQ, including parent’s education, income, and childhood lead exposure. In addition to controlling for these factors the Mexican researchers helped eliminate a source of bias by “blinding” the psychologist conducting the IQ tests so that the examiner did not know which children had, or did not have, high fluoride exposures.
According to the authors:
“We found that exposure to F (fluoride) in urine was associated with reduced Performance, Verbal, and Full IQ scores before and after adjusting for confounders. The same pattern was observed for models with F in water as the exposure variable…. The individual effect of F in urine indicated that for each mg increase of F in urine a decrease of 1.7 points in Full IQ might be expected.”
In addition to assessing the effect of fluoride on IQ, the Mexican team studied the effect of arsenic as well and found similar results. Based on their data, the authors conclude that
“fluoride and arsenic in drinking water have a potential neurotoxic effect in children. It is urgent that public health measures to reduce exposure levels be implemented. Millions of people around the world are exposed to these pollutants and are therefore potentially at risk for negative impact on intelligence. This risk may be increased where other factors affecting central nervous system development, such as malnutrition and poverty, are also present. The risk is particularly acute for children, whose brains are particularly sensitive to environmental toxins. Furthermore, it would be advisable to reexamine the benefits of fluoride given the documented health risks.”
While some pro-fluoride supporters may attempt to dismiss the results of this study — since the levels of fluoride in the water (5-9 ppm) are higher than the levels added to water in fluoridation programs (0.7-1.2 ppm) — it would be short-sighted to dismiss such important findings on this basis. After all, the study was able to detect a statistically significant effect within a rather small (n=132) group of children. Since individuals vary widely in their sensitivity to chemicals, it is plausible, and indeed likely, that — if fluoride can cause IQ loss at 5 ppm in a small group of children (e.g. hundreds) — it could also cause IQ loss at lower levels in a much larger group of children (e.g. many millions).
Moreover, as noted by Dr. Kathleen Thiessen, a panelist from the National Research Council’s review of fluoride, there is “almost certainly overlaps” in the daily doses ingested by some of the Mexican children in the study and the daily doses ingested by some American children – especially when considering the myriad other sources of fluoride exposure now available in the US.
2) Fluoride, Arthritis, and the Specter of Misdiagnosed Skeletal Fluorosis in the US
It has been known since the 1930s that ingesting too much fluoride can cause stiff and painful joints. According to scientists who have studied this condition (commonly referred to as skeletal fluorosis), the joint damage caused by fluoride may mimic other, more common, forms of “arthritis,” making it easy to misdiagnose — especially by doctors who are not trained in detecting fluorosis.
According to the Centers for Disease Control, 1 in 3 adults in the US now suffer from some form of arthritis. Could fluoride be a contributing factor in some of these cases? It is probable, however, as detailed in the the NRC’s 2006 review, there has never been an adequate study to determine the prevalence of earlier stages of skeletal fluorosis in the US. The problem with this “research gap” was underscored this year by three studies, one from India and two from the US.
According to the Indian study by Gupta et al, a 35-year old woman who drank water with 1.9 ppm fluoride developed a subtle form of fluorosis that doctors initially suspected to be a form of “seronegative arthritis” (2a). Seronegative arthritis refers to a form of arthritis which mimics the symptoms of rheumatoid arthritis (RA), but lacks the autoantibodies diagnostic of RA. In this case study, the woman “presented with joint pain involving the lower back, both heels, and the knee for the past 3 years.” In addition to these joint pains, the patient suffered from “gastrointestinal disturbance” prompting the doctors to suspect “the possibility of enteropathic arthritis.” Enteropathic arthritis is a form of arthritis associated with inflammatory bowel diseases.
The doctors finally began to suspect the role of fluoride after x-rays revealed increased bone density in the pelvic area and calcification of some ligaments. After follow-up tests revealed elevated levels of fluoride in the patient’s drinking water (1.9 ppm), and slightly elevated levels of fluoride in the blood (0.05 ppm), the doctors diagnosed the patient as suffering from fluorosis.
Another study, published in the summer by doctors at the Mayo Clinic, reports that similar cases of fluorosis may be occurring in the US among habitual tea drinkers (tea often contains high levels of fluoride), especially those with weak kidney function (2b). In the study, the Mayo doctors detail the cases of 4 patients who developed bone pains, and in some cases gastrointestinal problems, from drinking too much tea. As with the Indian study, at least one of these patients had previously been misdiagnosed as having “arthritis.” The woman, who “developed chronic pain and stiffness in her lower back that progressed to include bilateral hip and knee pain”, had been treated for 7 years with various drugs “but with no improvement in symptoms.” It wasn’t until the Mayo Clinic doctors identified fluorosis as the cause of her pain, that the woman took steps to reduce her tea intake which led, at last, to an improvement in symptoms.
According to the Mayo doctors:
“Fluoride toxicity can present in an insidious manner, and clinicians may overlook its signs and symptoms. Unless recognized and the source of excessive fluoride identified and discontinued, fluoride toxicity can be both progressive and crippling.”
In yet another study, presented at the annual conference of the American Society for Bone and Mineral Research, doctors reported a similar scenario (2c). A 49-year old woman (without kidney disease) developed skeletal fluorosis by drinking too much instant tea made with fluoridated water. As with the above cases, the woman “developed widespread musculoskeletal pains” and was misdiagnosed for years as having fibromylagia and osteoarthritis. According to the authors:
“we surmise that habitual consumption of 3 quarts daily of some regular-strength preparations for more than 10 years, especially if made with fluoridated water, could cause clinically significant skeletal fluorosis…. This fluoride exposure seems possible for many individuals who like instant or bottled teas. In fact, when a 36-year old coworker learned of our index case, she confided drinking 3-4 qts daily of what she described as a triple strength preparation of Nestea dissolved in unfiltered, municipal tap water over the past year… With increasing use of DXA, additional instances of skeletal fluorosis from instant tea will likely be revealed…”
3) CDC Releases New National Data on Dental Fluorosis in American Children
When children ingest too much fluoride they are at risk of developing a condition known as dental fluorosis. In its milder forms, dental fluorosis produces cloudy spots and streaks on the teeth, while in its advanced forms fluorosis can weaken the enamel and cause it to crumble and break. Fluoride causes these conditions by accumulating within the tooth and interfering with the tooth’s normal mineralization process. By interfering with tooth mineralization, dental fluorosis represents a toxic effect of fluoride, and thereby raises the larger question of what other (less visible) tissues in the body may be similarly affected. As noted by the Environmental Working Group:
“Fluorosis is the result of fluoride rearranging the crystalline structure of a tooth’s enamel as it is still growing. It is evidence of fluoride’s potency and ability to cause physiologic changes within the body, and raises concerns about similar damage that may be occurring in the bones.”
The extent to which dental fluorosis provides a visible indication of systemic harm remains a contested issue. What is not contested, however, is that millions of American children now have some form of it, with fluoridated water one of the main causes.
In 2007, the Centers for Disease Control released the latest national survey data on the rate of dental fluorosis among US teenagers (3). The survey, conducted between 1999 and 2004 by CDC’s National Health and Nutrition Examination Survey (NHANES), found that 41% of 12-15 year olds, and 36% of 16-19 year olds, have dental fluorosis. In other words, over 1 in 3 American teenagers now display a visible sign of fluoride overexposure. This is the highest national rate of fluorosis ever recorded in the US, far higher than the 1-10% range found in the 1940s, and considerably higher than the 23% found to be affected in the 1980s.
Not only has the prevalence of fluorosis increased, but its severity has increased as well. Whereas 1.4% of children had moderate or severe fluorosis in the 1980s, about 3.5% of children have it today, almost a three-fold increase. Both moderate, and severe, fluorosis are very disfiguring conditions that may embarass and cause psychological stress to a child, particularly if present on the front two teeth. According to the National Research Council, severe fluorosis may also cause adverse effects on a child’s health by weakening the protective function of the tooth’s enamel.
4) Silicofluorides Linked (Again) to Lead Exposure Risk
Can water fluoridation increase the levels of lead circulating in a child’s blood? This is the question that has been asked ever since Dartmouth professor Roger Masters, and chemical engineer, Myron Coplan, published studies in 1999 and 2000 reporting that exposure to “silicofluoridated” water was associated with increased blood lead levels in children surveyed in Massachusetts and New York State. In 2007, two new studies have added yet further evidence to this issue.
One of the studies, a tightly controlled laboratory experiment conducted by scientists at the University of North Carolina, submerged lead-containing brass pipes in water with various water treatment chemicals, including silicofluorides (4a). The study found that silicofluorides increased the erosion of lead from the piping, particularly when added in conjunction with chloramines (a disinfectant commonly used as an alternative to chlorine). According to the authors:
“Prior to the present study, no one had looked at brass corrosion by combinations of either chlorine or chloramine with water fluoridating agents. Several factors applicable to such combinations can produce more corrosion than either of the disinfectants or fluoridating agents alone.”
One caveat to this laboratory study is that the researchers added silicofluorides at a concentration of 2 ppm, which is slightly higher than the levels commonly added to drinking water (0.7-1.2 ppm). A new analysis of national data from NHANES (Macek 2006), however, suggests that silicofluorides at 1 ppm may also enhance lead levels (4b).
The analysis — conducted by Coplan and one of the lead authors of the North Carolina laboratory study — found that children drinking water with silicofluorides have an elevated, statistically-significant, risk of exceeding the hazard threshold for lead in blood (5 ug/dL) -– although the risk was not as great as previously estimated. According to this new data, the use of silicofluorides appeared to increase the lead risk in about 2 of every 100 children exposed — a notable difference considering that over 100 million Americans consume “silicofluoridated” water.
5) NRC Panelists Release Risk-Assessment on Fluoride
In its 2006 review, the National Research Council (NRC) concluded that the current allowable limits of fluoride in water in the US (4 ppm) are too high and should be lowered. The NRC didn’t specify what the new level should be, but recommended that the Environmental Protection Agency (EPA) conduct a new risk assessment which takes into account the new data identified in the report.
Since EPA has yet to conduct this risk assessment, 3 of the panelists from the NRC review –- along with a scientist representing EPA’s Headquarters Union — presented the results of their own risk assessment (5). According to the scientists:
“The purpose of this study was to conduct a risk analysis comparison between fluoride and other non-essential elements (e.g. Antimony, Arsenic, Beryllium, Cadmium, Mercury, and Thallium). Using recently published literature on fluoride toxicology, we calculated new reference doses (RfD) for fluoride based on several endpoint outcomes and used these to recommend a range of new MCLGs (Maximum Contaminant Level Goals) to help guide the EPA in adjusting the MCLG for fluoride in drinking water.”
This risk-assessment, which was presented at a Society of Toxicology conference in March, contradicts claims made by fluoridation proponents that the NRC report is not relevant to the policy of water fluoridation. According to the NRC scientists, if the same protocols used to evaluate other non-essential elements are used in the fluoride risk-assessment, than the safe water level for fluoride should be no higher than 0.4 ppm, which is lower than the levels (0.7-1.2 ppm) added to water for fluoridation.
According to the scientists:
“Our results indicated that in all calculations the new MCLG for fluoride in drinking water should be at most one tenth (0.4 mg/L) of the current MCLG of 4 mg/L, suggesting that the practice of fluoridation should be re-evaluated.”
6) Low-Level Fluoride Linked to Sperm Damage in Animals
When given at high doses, fluoride has been found to damage virtually any tissue in the body, whether it be the thyroid, the brain, or the reproductive system. On this, there is now little debate. What is still disputed, however, is whether low levels of fluoride can also cause harm. Towards this end, it will be important for researchers conducting animal studies in the future to put greater focus on low-level effects than has heretofore been the case. In 2007, two research teams did this, in separate investigations of how fluoride ingestion may affect sperm function.
The two studies examined the effect of water fluoride concentrations ranging from 1 to 10 ppm. Since rats and mice are significantly more tolerant to fluoride than humans, 1 to 10 ppm represents a notably low level of fluoride for these animals. It has been estimated, for example, that rats are 5 times less sensitive to fluoride than humans (Turner 1996), and thus a 4.5 ppm concentration would be roughly equivalent to 1 ppm for humans, while 10 ppm fluoride would be roughly equivalent to 2 ppm. It is striking, therefore, that these 2 studies found damaging effects of fluoride on sperm at these levels.
In the study by Reddy et al, 4.5 ppm (the lowest level tested) was associated with a reduction in sperm count and viability, as well as a reduction in testicular enzyme activity.
In the study by Dvorakova-Hortova et al, 10 ppm was associated with an impairment in “sperm capacitation” – the complex series of events which enable sperm “to obtain full fertilizing capacity.” The authors did not find the same effect from fluoride at 1 ppm. However, when 1 ppm fluoride was combined with aluminum, a similar effect was observed. (It is unclear whether this latter result was an effect of the aluminum itself, or an interactive effect of the aluminum and fluoride.)
As noted by Reddy, “extrapolation of rat data to human beings is always difficult” and, indeed, it is doubtful that the effects observed in these studies would be seen at the same relative levels in humans. Nevertheless, the two studies taken together, do raise added concern about fluoride’s effects on the reproductive system — especially when considering an earlier study conducted by the then-FDA scientist, Stan Freni, who found a correlation between water fluoride levels exceeding 3 ppm and decreased birth rates in the US. As noted by the NRC (2006) review, “the relationship between fertility and fluoride requires additional study.” These 2 studies add further weight to NRC’s conclusion.
7) U.S. Dentists “Unaware” of Recent Fluoride Research
When water fluoridation was first introduced en masse in the 1950s, dentists argued that fluoride needed to be ingested by children — while their teeth are developing — in order to be effective. This argument, which also underpinned the introduction of fluoride drops and pills, was based on the belief that ingested fluoride would accumulate in developing teeth and make the “fluoride-enriched” teeth stronger for life. Over the past 30 years, however, this theory has been put to the test and almost unanimously rejected by dental researchers (Featherstone 2000; Fejerskov 2004). A new theory has taken its place: Fluoride’s primary benefits do not come from being swallowed, but come instead from being applied topically to the outside of the tooth while in the mouth.
While the Centers for Disease Control (CDC) was late in coming to terms with this new paradigm on fluoride, it finally came on board in 1999. According to a 1999 report issued by the CDC, fluoride’s actions “primarily are topical for both adults and children.” CDC repeated this position again in 2001, stating: “fluoride’s predominant effect is posteruptive and topical.”
The implications of this new consensus are as obvious as they are important: If fluoride has little benefit when swallowed, there is no need for a fluoride chemical to ever make it past the mouth and into the bloodstream. As noted by the recent Nobel Laureate in Medicine, Dr. Arvid Carlsson, “in pharmacology, if the effect is local, it’s awkward to use it in any other way than as a local treatment. I mean this is obvious. You have the teeth there, they’re available for you, why drink the stuff?”
However, despite the fact that CDC is now on record stating fluoride’s benefits are primarily topical, a study published in the Journal of Public Health Dentistry reports that most practicing dentists and dental hygienists are not yet aware of this development. According to the study — which surveyed dentists and dental hygienists from Indiana and Illinois — only a small minority of dental professionals are aware of the new research. In Indiana, for example, only 25% of surveyed dentists correctly identified the topical effect of fluoride, while in Illinois, the respective figure was just 14%. According to the authors:
“Our main findings are a) that in 2005, 4 years following the release of the CDC’s sentinel recommendations, a considerable proportion of dental professionals in Indiana still did not understand fluoride’s predominant mode of action.”
Not only were the dentists behind in their knowledge of fluoride research, but the survey also found they didn’t even know basic information about fluoride, such as how much fluoride is in toothpaste or high-fluoride gels. As noted by the authors: “Another important finding was the inability of respondents to correctly identify the concentration of commonly used fluoride products.”
This raises the question: If, after 60 years of water fluoridation, most dentists still don’t know how fluoride actually works, or how much fluoride is in the products they prescribe, what else do they not know? Do they know how fluoride affects other tissues in the body besides the teeth?
8) No Link Found Between (Low-Fluoride) Bottled Water and Tooth Decay
Over the past decade, there has been a steady drumbeat of press warning of the risks from drinking bottled water. The idea — kept alive by press releases from dental associations — is that because most bottled waters have low levels of fluoride, people switching from tap water (which is usually fluoridated) to bottled water will not receive a sufficient intake of fluoride to ward off tooth decay.
One of the things that has been absent in the discussion about bottled water’s “threat” to teeth, is the lack of empirical evidence to justify the claim. It was a significant development this year, therefore, when researchers from the NIH-funded “Iowa Fluoride Study” published a study which provides some actual hard data on the issue (8).
For the past decade, these researchers have been carefully monitoring the fluoride intake of hundreds of Iowan children, from birth through adolescence. From this group of children, the researchers separated out those children who regularly used bottled water. They then compared the tooth decay history of these bottled water drinkers with children who regularly drank tap water (most of which was fluoridated). Even when controlling for important variables, such as socioeconomic status and toothbrushing frequency, the authors found no relationship between bottled water use and tooth decay (in baby or permanent teeth), even though the fluoride intake of the bottled water users was significantly lower than the tap-water users.
According to the authors:
“Presumably, such reduced exposure to fluoride would result in increased caries occurrence. However, the present study did not find any significant differences in caries prevalence or incidence between bottled water users and those who did not use much bottled water.”
Due to the limited number of bottled-water users identified in this group of Iowan children, however, the authors recommend that larger studies be conducted in order to reach more definitive conclusions.
9) Fluoridated Water for Adults: Very Little, If Any, Benefit
Historically, most of the research on whether water fluoridation has a benefit, has been focused on children. By way of contrast, only a small handful of studies have ever examined the effectiveness of fluoridated water for adults. According to a 2001 review by the Ontario Ministry of Health and Long Term Care (Locker 2001), “The absence of adults from water fluoridation studies is difficult to explain… Whatever the reason, it must be regarded as a major limitation in the research effort to date.”
In 2007, an important study was published which sheds light on whether fluoridated water is effective at preventing tooth decay in adult populations (9a). Despite a recent press release to the contrary, the study indicates very little, if any, benefit.
To assess fluoridation’s effectiveness, the study examined the dental treatment costs accrued over 5 years by 51,683 members from an HMO. The HMO members, including both adults and children, lived in fluoridated and non-fluoridated communities of 3 separate regions in the Northwest. The authors, a team of pro-fluoridation researchers, state that the study shows a “small” benefit from fluoridated water which “may” have led to some cost-savings. A close inspection of their data, however, shows that this “small benefit” — if it even exists — was very small indeed.
For example, in the largest region examined in the study, representing over 75% of the HMO members surveyed (the Portland metro area of Oregon), fewer children and adults in the non-fluoridated areas required treatment than children and adults in the fluoridated areas. Moreover, the children and adults in the non-fluoridated area who sought treatment accrued lower total costs over the 5-year period than those in the fluoridated area. As noted by the authors, the “Portland metro had lower treatment costs for the NF (Non-Fluoridated) area…”
These findings from the Portland region are remarkable: after all, one of the most-frequently cited claims by fluoridation proponents is that every $1 spent on fluoridated water saves $80 in dental bills. In this study, the dental care costs in the largest region surveyed were lower in the areas without water fluoridation.
Even among the the smaller regions in the study (Marion County, Oregon and Clark County, Washington), which produced more favorable results for the fluoridated areas, the results were still inconsistent and the benefits marginal. As the authors admit, “the effect we observed was generally small.”
One of the reasons given by the authors for why the benefit was small and inconsistent was that the population being studied was insured and had ready access to dental care and preventive procedures. However, a separate study by a University of Michigan research team suggests that water fluoridation is equally ineffective in low-income areas as well (9b). The study examined a group of 800 low-income African American adults living in Detroit. Despite the fact that Detroit has been fluoridated since 1967, the authors found that tooth decay was “severe” and “extensive”, with tooth decay rates reaching as high as 99.8% for individuals aged 14 to 35 years.
What makes this Detroit study particularly interesting, is that — unlike the vast majority of studies investigating fluoridation’s effectiveness — the authors actually assessed the quantity of fluoridated tap water consumed by each individual. When they then compared the quantity of fluoridated water consumed with the rate of tooth decay, they found no relationship. In other words, ingestion of fluoridated tap water for up to 4 decades did nothing to produce better teeth in this disadvantaged population.
10) Second Thoughts About Water Fluoridation
Several authors of the studies noted above have advised that the use of fluoride for the prevention of tooth decay be re-evaluated in light of red flags surrounding its health effects. In 2007, two reviews attempted to re-evaluate water fluoridation’s purported benefits. The reviews, one published in the British Medical Journal (BMJ) and the other in the dental journal Clinical Oral Investigations, have helped to advance the fluoridation debate by elucidating some (not all) key points which critics have been raising in recent years (10a,b).
According to the BMJ review, the evidence underpinning water fluoridation is of “poor quality.” Indeed, if fluoridated water were defined as a medical treatment — which the authors suggest is a reasonable characterization — there would be insufficient evidence to justify its continuation. As noted by the authors:
“If fluoride is a medicine, evidence on its effects should be subject to the standards of proof expected of drugs, including evidence from randomized trials… There have been no randomized trials of water fluoridation.”
Highlighting the uncertainties surrounding water fluoridation, the authors point out that international tooth decay rates appear entirely unrelated to the water fluoridation status of each country. The authors state:
“Although the prevalence of caries varies between countries, levels everywhere have fallen greatly in the past three decades, and national rates of caries are now universally low. This trend has occurred regardless of the concentration of fluoride in water or the use of fluoridated salt, and it probably reflects use of fluoridated toothpastes and other factors, including perhaps aspects of nutrition.”
In addition to questioning the magnitude of fluoridation’s benefits, the authors point out that — after 60 years — its safety has yet to be established. The published studies purporting to prove fluoridation’s safety are, according to the review, “insufficient to rule out all but the biggest effects.” As a result, the authors suggest that:
“In the case of fluoridation, people should be aware of the limitations of evidence about its potential harms and that it would be almost impossible to detect small but important risks (especially for chronic conditions) after introducing fluoridation.”
Consistent with the BMJ review, a review in the journal Clinical Oral Investigations examined the research on fluoridation’s effectiveness between the years 2001 and 2006 and found that water fluoridation “may be unnecessary.” According to the authors:
“For the past 50 years, CWF (Community Water Fluoridation) has been considered the most cost-effective measure for the control of caries at the community level. However, it is now accepted that systemic fluoride plays a limited role in caries prevention. Several epidemiologic studies conducted in fluoridated and nonfluoridated communities clearly indicated that CWF may be unnecessary for caries prevention, particularly in the industrialized countries where the caries level has [become] low.”
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6a) Reddy PS, et al. (2007). Suppression of male reproduction in rats after exposure to sodium fluoride during early stages of development. Naturwissenschaften 94(7):607-11.
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10b) Pizzo G, et al. (2007). Community water fluoridation and caries prevention: a critical review. Clinical Oral Investigations 11(3):189-93.
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