Since the 2024 election, removal of fluoride from public drinking water has been proposed because of concerns that fluoride causes cancer. In this post, I will review the actual data about fluoride and cancer and will argue that fluoride should not be removed from public water supplies. The campaign for fluoridation was led by dentists and not physicians. Oral health is something that most physicians know very little about. Since dentists are generally not a presence in American hospitals, most physicians are unfamiliar with the reasons for or risks of fluoridation. But because physicians, and not dentists, are the experts in non-oral cancers, we need to be familiar with the fluoridation literature in order to knowledgeably participate in public health debates.
Fluoride is the anionic version of the element fluorine that is found in natural water sources. It is a common component of rocks and is the 13th most abundant element on the surface of the Earth. The amount of fluoride in natural water sources varies, depending on geographic location and the amount of mineral fluoride in local rocks and soils. For example, seawater averages 1.1 mg/L of fluoride and freshwater fluoride levels can range from 0.05 to 8 mg/L.
In the early 1900’s, dentists noticed that children in communities with high levels of naturally-occurring fluoride in the city water system had fewer dental caries than children in communities with low city water fluoride levels. Based on these observations, in 1945, the City Commission of Grand Rapids in Michigan voted to add fluoride to the city’s public water system. The rate of cavities in children born after fluoridation dropped by 60%. Shortly after, other U.S. cities as well as foreign countries added fluoride to drinking water and found similar reductions in the rate of childhood cavities. Overall, fluoridation reduces dental caries by about 25%. In 1951, fluoridation became an official policy of the U.S. Public Health Service. In 1962, the Federal government updated its drinking water standards to state that the optimal level of fluoride should be 0.7 to 1.2 mg/L. Fluoridation became a recommendation but not a requirement, allowing individual communities to decide for themselves whether or not to add fluoride to city water supplies. In some cities, the fluoride levels were naturally above 0.7 mg/L in water sources and it was unnecessary to add additional fluoride. However, the natural water sources for most U.S. cities have levels of fluoride below 0.7 mg/L and the majority of these cities add additional fluoride to achieve levels above 0.7 mg/L. The fluoride level in domestic water wells depends on geographic location, the depth of the well, and the geology of the rocks containing groundwater. About 15% of U.S. wells have fluoride levels above 0.7 mg/L. Currently, 77% of Americans have tap water that has the recommended 0.7 mg/L or more of fluoride, either because their water naturally contains enough fluoride or because fluoride is added to the municipal water supply.
Here in Ohio, a state law was passed in 1969 requiring fluoridation of city water supplies. However, individual cities could vote to opt out of fluoridation by a referendum. Lancaster, Ohio was one of the cities that voted to not add fluoride to the city water supplies. Lancaster is only about 30 miles from Columbus, so I had a lot of patients from Lancaster. For my patients younger than 60-years-old, I could tell if they grew up in Lancaster because when I would do physical exams, those from Lancaster always had teeth full of fillings or had lots of teeth removed. Those from other Central Ohio communities generally had pretty good teeth.
So, it is pretty clear that fluoridation reduces dental caries. And getting cavities in your teeth is not an entirely benign thing. Dental caries can affect quality of life by resulting in mouth pain, bad breath, difficulty chewing, and loss of teeth. They can also affect a person’s health by causing dental abscesses and chronic inflammation that in turn can affect children’s growth. They are financially costly, too – a dental filling to repair a cavity costs around $200 for silver amalgam and about $1,200 for a porcelain filling. If the cavity results in infection of the pulp of the tooth, the cost of a root canal is about $1,000. Since adults have 32 teeth, dental expenses can really ramp up in communities like Lancaster.
The reason the residents of Lancaster, Ohio voted to not put fluoride in the water supply was concern that fluoride causes cancer. This concern is also the reason why public figures such as Robert F. Kennedy, Jr. have advocated to ban fluoridation of water supplies. Most people would rather have a few cavities than have cancer, so what is the real story about fluoride and cancer.
Does fluoride cause cancer?
Fluoride is mainly taken up in the teeth and bones. Consequently, the cancers that have been suspected to be related to fluoride are bone cancers, particularly osteosarcoma. This is a relatively rare cancer, with a total of only about 1,000 cases per year in the U.S. The incidence of osteosarcoma has two peaks – one peak between the ages of 10-14 and a second peak in adults older than 65-years-old. Boys and men are affected with osteosarcoma more frequently than girls or women. Because of its rarity, studies about whether osteosarcoma is related to fluoride levels in water inevitably only involve very small numbers of subjects, making statistical significance difficult to achieve. Moreover, it is exceedingly difficult to be sure of the actual fluoride consumption by subjects in these studies since there can be significant variations in the amount of tap water a person consumes (as opposed to bottled water or other liquids), whether a subject’s tap water had a home filtering system, whether subjects had lived in multiple communities over the course of their lives with different levels of fluoride in the different communities, and the level of naturally-occurring fluoride in water systems that do not have fluoride chemically added.
Carcinogenicity studies generally start with animal studies and there have been several studies examining the effect of fluoride in drinking water in rats and mice. In one study, rats were given drinking water containing 175 mg/L of fluoride (250 times greater than the concentration that the Federal government has recommended for municipal water supplies). Four of the male rats in the fluoride groups developed osteosarcomas but none of the control rats developed osteosarcomas; female rats did not have an increase in osteosarcoma. With only 4 rats developing cancer, it is not really possible to establish a link between fluoride and osteosarcoma in rodents. A second study in rats two years later compared rats consuming drinking water with 250 mg/L fluoride (350 times greater than the recommended levels in municipal water supplies) and found no increase in osteosarcoma compared to control rats. Two additional studies in 1990 and 1993 fed rats and mice 25 mg/kg body weight and found no increase in the rate of cancer. Another study of mice fed high doses of fluoride found no increase in cancers. The bottom line is that there is no good evidence that even very high doses of fluoride causes cancer in rats.
Last month, a review of all of the scientific literature regarding fluoride and cancer in humans was published in the journal Bone. There have been 14 studies published – 12 of these found that fluoridation was not associated with bone cancer and 2 showed an increased risk of osteosarcoma in boys. Both of these latter two studies had significant flaws.
One human study had very small numbers of subjects – 12 boys under age 19-years-old developed osteosarcoma from communities with fluoridated tap water versus 8 boys developing osteosarcoma from communities without tap water fluoridation. These numbers are too low to make any confident conclusions about fluoride and cancer.
The other human study looked at 9 communities (3 states and 6 large cities) in the United States and determined the percentage of the population in each of those communities who had fluoridated water; for example, in Iowa (one of the states in the study), 70% of the population had access to fluoridated tap water whereas in Utah (also one of the nine areas in the study), only 2% of the population had access to fluoridated tap water. The study authors then looked at the incidence of various cancers in each of those 9 communities and did linear regression comparing the incidence of cancer to the percentage of the population with fluoridated tap water. They found a statistically significant relationship with osteosarcoma in boys – there was a higher incidence of osteosarcoma in communities with a higher percentage of the population having access to fluoridated public drinking water. This study has been cited by those opposed to fluoridation but what is usually not mentioned is that this same study found that prostate cancer, melanoma, lip cancer, and thyroid cancer were all less common in communities with a high percentage of population having access to fluoridated drinking water. So, if you use this study to conclude that fluoridation causes osteosarcoma, then you also have to conclude that fluoridation prevents prostate cancer. Furthermore, there are a lot of other differences between people who live in Utah versus those in Iowa – smoking prevalence, alcohol consumption, racial demographics, obesity, etc. and any of these other variables could just have easily been responsible. Another major flaw of this study is that it was based on the 1985 Fluoridation Census that reported the percentage of municipalities that added fluoride to public water supplies. Many public water supplies (particularly in the western U.S.) naturally contain high levels of fluoride and therefore do not add additional fluoride. So, in Utah, for example, 2% of the population were in communities where fluoride was added to the public water supply but we have no way of knowing how many of the other 98% of the population were in communities that naturally had enough fluoride in the water so that fluoridation was unnecessary. In other words, there is absolutely no way to know how much fluoride people in the different communities actually ingested.
Taken together, there is no convincing evidence that fluoride causes bone cancer in either rodents or humans. Since osteosarcoma is such a rare cancer, it remains possible that there is an effect on the incidence of fluoridation on osteosarcoma that is too small to detect in epidemiological studies. But given that existing negative studies have involved thousands of people, if there is a link between fluoride and cancer, it is incredibly minimal.
On the other hand, a recent meta-analysis found that tooth loss due to periodontal disease and inflammation doubles the risk of oral cancer. So, poor dental health may actually be a greater risk of getting cancer than fluoridation, especially since oral cancer is far more common than osteosarcoma.
Other sources of fluoride
The recommended daily consumption of fluoride to prevent tooth decay is 1 mg for young children and 3 mg for teenagers and adults. Foods naturally contain fluoride but only in very small amounts. For example, shrimp is one of the most fluoride-rich foods but only contains 0.17 mg of fluoride per 3 ounces. In order to get enough fluoride to prevent cavities, an adult would need to eat 3.3 pounds of shrimp every day.
Most toothpaste contains fluoride but since most people spit toothpaste out of their mouth after brushing, adults only get about 0.1 mg of fluoride per brushing. In order to get enough fluoride to prevent cavities from toothpaste, an adult would need to brush their teeth 30 times a day.
In the 1960’s, before our Columbus, Ohio municipal water supply was fluoridated, our dentist would administer fluoride gels directly to my teeth twice a year as a form of fluoride supplementation. However, the amount of fluoride absorbed is between 1 and 30 mg, meaning that a person would need to have fluoride gel treatments somewhere between three times a day and very 10 days, depending on absorption.
Fluoride is not usually included in most multivitamin and mineral supplements. However, fluoride supplements are commercially available and are an option for people living in communities that lack municipal fluoridation and for people dependent on well water when their water supply does not naturally have sufficient fluoride. Over-the-counter supplements containing 3 mg/tablet of fluoride are commercially available as are supplements available by prescription.
Arguments against fluoridation
Those opposed to drinking water fluoridation have posed a number of reasons why they believe that fluoride should be removed from municipal water supplies. The main argument has been the risk of osteosarcoma and as described above, this argument has largely been debunked. Fluoride opponents have also claimed that fluoride causes a plethora of other diseases including cognitive decline, arthritis, thyroid disease, brain damage, pineal gland damage, kidney disease, fluorosis, and impotence. These claims are dubious at best. For example, the studies suggesting fluoride reduces IQ all come from non-U.S. countries, such as India, where water supplies contain much higher levels of fluoride than in the U.S. (averaging 2.37 mg/L). No studies in the U.S. have shown that fluoride affects IQ.
The one argument made by fluoride opponents that does have merit is that fluoride ingestion can cause fluorosis. This is a condition where the enamel of the teeth can develop lacy white opacities (photo below) and in severe cases, the teeth can develop pits on their surface. Less than 1% of children ingesting fluoride develop severe fluorosis; however, a high percentage of children can develop mild or vert mild fluorosis. In the vast majority of cases, fluorosis is only a mild cosmetic concern but in very severe cases, it can require dental fillings when pits develop. However, the risk of getting a cavity requiring a dental filling by drinking non-fluoridated water is much greater than the risk of developing fluorosis severe enough to require a dental filling by drinking fluoridated water.
Opponents also argue that fluoridation is unethical because individuals cannot opt-out of fluoridation – in other words, individuals do not have the freedom to choose whether or not to fluoridate their drinking water. Although communities (such as Lancaster, Ohio) are legally able to vote to not fluoridate water, the argument is that if a referendum fails at the voting booth, the minority who opposed fluoridation are being discriminated against by being forced to drink fluoridated water. Opponents also argue that fluoridation discriminates against low-income families because high income families who do not want their children to ingest fluoride can afford to buy fluoride-free bottled water whereas low income families are too poor to buy fluoride-free bottled water. Another option is to buy charcoal filters for drinking water. Household charcoal filters remove about 50% of fluoride from tap water. I have 3 charcoal water filters that range in price from about $1 for the charcoal filter in my coffee maker to $10 for the in-line charcoal filter in my refrigerator’s water dispenser to $15 for a charcoal-filtered water pitcher that I bought last year.
What would happen if fluoride was banned from municipal water supplies?
If fluoridation goes away, many Americans who are concerned about dental health, and in particular the dental health of their children, will likely purchase fluoride supplements. This will open up a whole new market for supplement makers and we will likely see multivitamins with fluoride on the store shelves.
But the majority of Americans will likely not purchase fluoride supplements. Because it is not possible to get sufficient fluoride from food sources or from toothpaste, these people will have about a 25% increase in cavities. Those cavities will either need to get costly dental fillings or the teeth will ultimately need to be removed. Because 88% of Americans have dental insurance, this will result in a considerable rise in dental insurance premiums. Because Medicaid covers dental care, the Centers for Medicare and Medicaid Services (CMS) expenses will rise, resulting in greater costs to taxpayers. Currently, 38% of American children get dental care through taxpayer-funded Medicaid or CHIP. Taxpayers would have to pay for a lot of fillings in these kids. Most of the 12% of Americans without dental insurance will need to have decayed teeth removed in the future unless they pay out of pocket to get dental fillings. The increase in dental caries in the U.S. will result in an increased demand for dentist services; the law of supply and demand dictates that this will result in increased costs for dental care until the supply of dentists can be increased.
The drinking water in many communities naturally contains more than 0.7 mg/L of fluoride. This is particularly common in the western United States. For example, there are hundreds of communities in Texas where drinking water naturally contains more than 1.0 mg/L of fluoride and several communities with natural fluoride levels exceeding 5.0 mg/L – these communities do not add additional fluoride to their municipal water supply. As noted above, about 15% of U.S. domestic wells have well water naturally containing > 0.7 mg/L of fluoride. Americans living in these communities would not be affected by a ban on supplementing fluoride in municipal water supplies. Similarly, anyone who gets their drinking water from well water would be unaffected.
So, should doctors care about fluoridation?
The American Dental Association and the American Academy of Pediatrics both recommend fluoridation of public water supplies in communities where the naturally occurring fluoride levels are < 0.7 mg/L. The pediatricians make this recommendation because dental caries disproportionately affect the health of children. The dentists make this recommendation in part because there are not enough dentists to fill the tens of millions of new cavities and perform the increased numbers of root canals resulting from fluoride removal.
There are several reasons why (non-pediatric) physicians should be concerned about banning fluoride from public water supplies. First, it will increase Medicaid costs as well as dental insurance costs to all Americans. Second, we’re supposed to be the nation’s experts in cancer and the medical literature has shown that there is no convincing evidence that fluoridation causes cancer or any medical conditions other than dental fluorosis (and having fluorosis is not nearly as bad as having cavities). Third, just because oral health is not taught in medical schools does not mean that oral health is any less important than the health of other parts of the body.
Back in the 1960’s, before public water fluoridation, Crest toothpaste ran TV ads featuring kids that proudly told their fathers after their dental check-ups: “Daddy, Daddy, I only had 1 cavity!” Today, most children’s dentist visits result in no cavities. The CDC reports that the average American child develops only 2 cavities in their permanent teeth during their entire childhood. Personally, I don’t want to go back to a time where having only one cavity at each dental visit was a reason to rejoice.
December 20, 2024
