Fluoride in Drinking Water: A Review of Fluoridation and Regulation Issues

Fluoride in Drinking Water: A Review of
Fluoridation and Regulation Issues
Updated November 26, 2008
Mary Tiemann
Specialist in Environmental Policy
Resources, Science, and Industry Division

Fluoride in Drinking Water:
A Review of Fluoridation and Regulation Issues
Summary
According to the Centers for Disease Control and Prevention (CDC), 67% of the
246 million people in the United States who receive their water from a public water
system received fluoridated water in 2000. One of the CDC’s national health goals
is to increase the proportion of the U.S. population served by community water
systems with “optimally” fluoridated drinking water to 75% by 2010. The decision
to add fluoride to a water supply is made by local or state governments. The U.S.
Public Health Service (PHS) has recommended an optimal fluoridation level in the
range of 0.7 to 1.2 milligrams per liter (mg/L) for the prevention of tooth decay.
The fluoridation of drinking water often generates both strong support and
opposition within communities. This practice is controversial because fluoride has
been found to have beneficial effects at low levels and is intentionally added to many
public water supplies; however, at higher concentrations, it is known to have toxic
effects. The Environmental Protection Agency (EPA) regulates the amount of
fluoride that may be present in public water supplies to protect against fluoride’s
adverse health effects. Fluoridation opponents have expressed concern regarding
potential adverse health effects of fluoride ingestion, and some view the practice as
an undemocratic infringement on individual freedom. The medical and public health
communities generally have recommended water fluoridation, citing it as a safe,
effective, and equitable way to provide dental health protection community-wide.
Because the use of fluoridated dental products and the consumption of food and
beverages made with fluoridated water have increased since the PHS recommended
optimal levels for fluoridation, many people now may be exposed to more fluoride
than had been anticipated. Consequently, questions have emerged as to whether
current water fluoridation practices and levels offer the most appropriate ways to
provide the expected beneficial effects of fluoride while avoiding adverse effects
(most commonly, tooth mottling or pitting — dental fluorosis) that may result from
ingestion of too much fluoride when teeth are developing. Also, scientific
uncertainty regarding the health effects of exposure to higher levels of fluoride add
controversy to decisions regarding water fluoridation.
Although fluoride is added to water to strengthen teeth, some communities must
treat their water to remove excess amounts of fluoride that is present either naturally
or from pollution. In 1986, EPA issued a drinking water regulation for fluoride that
includes an enforceable standard (maximum contaminant level [MCL]) and an MCL
goal (MCLG) of 4 mg/L to protect against adverse effects on bone structure. EPA
acknowledged that the standard did not protect infants and young children against
dental fluorosis, which EPA considered a cosmetic effect rather than a health effect.
To address this concern, EPA included in the regulation a secondary (advisory)
standard of 2 mg/L to protect children against dental fluorosis and adverse health
effects. As part of its review of the fluoride regulation, EPA asked the National
Research Council (NRC) to review the health risk data for fluoride and to assess the
adequacy of EPA’s standards. In March 2006, the NRC released its study and
concluded that EPA’s 4 mg/L MCLG should be lowered.

Contents
In troduction ..................................................1
Background ..................................................2
Questions About the Safety and Benefits of Fluoridation...............5
Dental Fluorosis...........................................5
Health Effects.............................................7
Effi cacy ................................................10
Other Considerations......................................11
Regulation of Fluoride in Drinking Water..........................12
Standard Setting..........................................12
Fluoride Standards........................................13
EPA Fluoride Standards Review.............................14

2006 NRC Review of EPA’s Fluoride Standards:

Findings and Recommendations.............................15
Dental Fluorosis..........................................16
Skeletal Fluorosis.........................................16
Bone Fractures...........................................16
Carcinogenicity ..........................................17
Other Potential Effects.....................................17
Research Needs..........................................18
NRC Recommendations...................................18
Conclusion ..................................................19

Fluoride in Drinking Water:
A Review of Fluoridation and
Regulation Issues
Introduction
The fluoridation of drinking water often generates both strong support and
opposition within communities. The practice is recommended by the U.S. Public
Health Service to prevent tooth decay. The decision to fluoridate a public water
supply is made by the state or local municipality and is not mandated by any federal
agency. Opponents have expressed concern regarding potential adverse health effects
of exposure to fluoride, and some view the practice as an undemocratic infringement
on individual freedom. The medical and public health communities generally have
supported water fluoridation, citing it as a safe, effective, and equitable way to
provide dental health protection community-wide.
With the increased use of products containing fluoride, such as toothpaste and
rinses, questions have emerged as to whether current fluoridation practices and levels
are necessary and offer the most appropriate way to provide the beneficial effects of
fluoride while avoiding adverse effects (such as tooth mottling or dental fluorosis)
that can result from exposure to too much fluoride. Moreover, research gaps
regarding the potential health effects of exposure to increased amounts of fluoride
and among different age groups continue to add controversy to decisions regarding
water fluoridation.
Although many communities add fluoride to drinking water to strengthen teeth,
some communities must treat their water to remove excess amounts of fluoride,
which often is present naturally in water. The Environmental Protection Agency
(EPA) regulates the maximum amount of fluoride that may be present in public
drinking water supplies to protect against certain adverse health effects.
In 1986, EPA issued a drinking water regulation for fluoride that includes an
enforceable standard (a maximum contaminant level [MCL]) and a non-enforceable
health-based maximum contaminant level goal (MCLG) of 4 milligrams per liter
(mg/L) to protect against adverse effects on bone structure. EPA acknowledged that
the standard did not protect infants and young children against dental fluorosis, which
EPA considered a cosmetic effect rather than a health effect. To address concerns,
EPA included in the regulation a secondary (advisory) standard of 2 mg/L to protect
children against dental fluorosis and adverse health effects. As part of its ongoing
review of the fluoride regulation, EPA asked the National Research Council (NRC)
of the National Academies of Science to review the health risk data for fluoride and
to assess the adequacy of EPA’s standards. On March 22, 2006, the NRC released its
study and concluded that EPA’s 4 mg/L MCLG should be lowered.

This report discusses the potential benefits and adverse effects associated with
the fluoridation of drinking water supplies. It also discusses the regulation of fluoride
in drinking water to protect against adverse health effects from exposure to higher
levels of fluoride, and it reviews the status of federal efforts to update the health risk
assessment for fluoride and the drinking water standard for fluoride. The following
review of issues related to fluoride in drinking water presents information from
research published in peer-reviewed scientific journals, reports and statements of
federal agencies (including the Centers for Disease Control and Prevention [CDC]
and the U.S. Public Health Service [PHS]) and the World Health Organization,
studies by the National Research Council, and other sources.
Background
Fluoride is a naturally occurring substance and is present in virtually all water,
usually at very low levels. Higher concentrations of naturally occurring fluoride often
are associated with well water, where fluoride has dissolved from the rock formations
into the groundwater.¹ Community water fluoridation began in 1945, after scientists
discovered that higher natural levels of fluoride in a community water supply were
associated with fewer dental caries (cavities) among the residents.²
In 2004, the Surgeon General reported that more than 170 million (67%) of the
people in the United States who received their water from a public water system
received fluoridated water.³ This represented a 5% increase from 1992, when 62%
of individuals served by public water systems were provided with fluoridated water.⁴
Many public health agencies and professional health organizations have
advocated the addition of a small amount of fluoride to drinking water to help
strengthen teeth and prevent dental caries. Although this practice has been
controversial in various communities, the CDC, the American Medical Association,
the American Dental Association (ADA), the American Academy of Pediatric
Dentistry, and others have recommended fluoridation of public water supplies as an
effective way to protect dental health. This approach has been advocated for its
ability to provide community-wide benefits, particularly in poorer communities
where children may be less likely to receive adequate dental care.⁵

¹ Fluoride also occurs in many foods, including meat, potatoes, fish, sugar, milk, and
legumes. The amount in brewed tea ranges from 1 to 6 milligrams per liter (mg/L),
depending on brewing strength and time. Also, fluorides are used industrially and may be
present in the environment as a result of inadequate pollution control.
² National Cancer Institute, Cancer Facts: Fluoridated Water, National Institutes of Health.
³ Dr. Richard Carmona, U.S. Surgeon General, Surgeon General’s Statement on Community
Water Fluoridation, Department of Health and Human Services, 2004.
⁴ Centers for Disease Control and Prevention, “Populations Receiving Optimally Fluoridated
Public Drinking Water — United States, 2000,” Morbidity and Mortality Weekly Report,
vol. 51, no. 7, February 21, 2002, pp. 144-147.
⁵ Centers for Disease Control and Prevention, “Achievements in Pubic Health, 1900-1999:
Fluoridation of Drinking Water to Prevent Dental Caries,” Morbidity and Mortality Weekly
(continued...)

The CDC considers the reduction in tooth decay from fluoridation one of the top
public health achievements of the 20^th Century.⁶ In 2002, the CDC reported that
[d]uring the second half of the 20^th century, a major decline in the prevalence and
severity of dental caries resulted from the identification of fluoride as an
effective method of preventing caries. Fluoridation of the public water supply is
the most equitable, cost-effective, and cost-saving method of delivering fluoride⁷
to the community.
One of the CDC’s national health goals for 2010 is to increase the proportion
of the U.S. population served by community water systems with “optimally”
fluoridated drinking water to 75%.⁸ The optimal fluoridation level recommended by
the U.S. Public Health Service for decay prevention is in the range of 0.7 to 1.2
milligrams per liter (mg/L).
The World Health Organization (WHO) has identified dental caries (cavities)
as a worldwide epidemic and recommends adding fluoride to drinking water where
naturally occurring levels of fluoride are below optimal levels.⁹ The WHO states that
the goal of community-based public health programs “should be to implement the
most appropriate means of maintaining a constant low level of fluoride in as many
mouths as possible.”¹⁰ According to the WHO,
[w]ater fluoridation in low fluoride-containing water supplies helps to maintain
optimal dental tissue development and dental enamel resistance against caries
attack during the entire life span.... People of all ages, including the elderly,
benefit from community water fluoridation. For example, the prevalence of
caries on root surfaces of teeth is inversely related to fluoride levels in the
drinking water: in other words, within the non-toxic range for fluoride, the higher
the level of fluoride in water, the lower the level of dental decay. This finding
is important because with increasing tooth retention and an aging population, the

⁵ (...continued)
Report, vol. 48, no. 41, October 22, 1999, pp. 933-940. Available online at
[ h t t p : / / www.cdc.go v/ mmwr / pr evi e w/ mmwr h t ml / mm4841a1.ht m] .
⁶ Centers for Disease Control and Prevention, “Ten Great Public Health Achievements —
United States, 1900-1999,” Morbidity and Mortality Weekly Report, vol. 48, no. 12, April

2, 1999, pp. 241-243. See [http://www.cdc.gov/mmwr/preview/mmwrhtml/00056796.htm].

⁷ Centers for Disease Control and Prevention, Populations Receiving Optimally Fluoridated
Public Drinking Water, pp. 144.
⁸ U.S. Department of Health and Human Services, Healthy People 2010 — Understanding
and Improving Health, 2^nd ed., Washington, DC, U.S. Government Printing Office,
November 2000, pp. 21-28.
⁹ World Health Organization, Water Sanitation and Health, World Water Day 2001: Oral
Health: Dental Caries, a Worldwide Epidemic, Health and Sanitation Unit and Oral Health
Program.
¹⁰ World Health Organization, Risks to Oral Health and Intervention: Fluoride. See
[ ht t p: / / www.who.i nt / or a l _heal t h/ act i on/ r i sks/ en/ i ndex1.ht ml ] .

prevalence of dental root caries would be expected to be higher in the absence¹¹
of fluoridation.
The recommended beneficial amount of fluoride can be obtained from a variety
of sources other than water (e.g., fluoride toothpastes, rinses, and supplements).
However, health officials historically have recommended fluoridation of community
water supplies, citing socioeconomic reasons that may vary among countries and
communities. The WHO explains this preference as follows:
The consensus among dental experts is that fluoridation is the single most
important intervention to reduce dental caries, not least because water is an
essential part of the diet for everyone in the community, regardless of their
motivation to maintain oral hygiene or their willingness to attend or pay for
dental treatment. In some developed countries, the health and economic benefits
of fluoridation may be small, but particularly important in deprived areas, where¹²
water fluoridation may be a key factor in reducing inequalities in dental health.
Despite such recommendations, fluoridation remains far from universally
practiced. Worldwide, an estimated 350 million people receive artificially fluoridated
water, and another 50 million drink water that is naturally fluoridated at or near the¹³
optimal level. Overall, some 40 countries practice water fluoridation, and the
percentage of populations receiving artificially fluoridated water varies greatly.
Countries where fluoridation is practiced (and the percentage of their populations
receiving fluoridated water) include Argentina (21%), Australia (61%), Brazil (41%),
Canada (43%), Chile (40%), Colombia (80%), Israel (75%), Malaysia (70%), New
Zealand (61%), and Singapore (100%).¹⁴ Of the Western European countries, the
Republic of Ireland (73%), Spain (10%), and the United Kingdom (10%) fluoridate
drinking water. Most other Western European countries have ceased, or never
practiced, water fluoridation for various reasons, including the availability of other
sources of fluoride (especially toothpaste), the availability of free school-based dental
care programs in some countries, broader public skepticism about the safety and
efficacy of fluoridation, and greater political opposition. In several Latin American
countries, where centralized water supplies are often lacking, fluoridated salt is the
chosen method of providing dental protection across disparate communities.
Fluoridated salt also is available in some European countries, including Austria,
France, Germany, Hungary, and Switzerland.¹⁵

¹¹ Ibid.
¹² World Health Organization, Naturally Occurring Hazards. Available online at
[ ht t p: / / www.who.i nt / wat er _sani t a t i on_heal t h/ nat ur al haza r ds.ht ml #f l uor i de] .
¹³ British Fluoridation Society and the UK Public Health Association, One in a Million: The
Facts about Water Fluoridation, 2^nd ed., 2004, p. 71.
¹⁴ Mullen, J. History of Water Fluoridation, British Dental Journal, 2005. p. 1-4
¹⁵ Marthaler, T. M. Salt Fluoridation in Europe, Comparisons with Latin America,
Department of Preventive Dentistry, Periodontology and Cardiology, University of Zurich,
available at [http://www.sph.emory.edu/PAMM/SALT2000/marthaler.pdf].

Questions About the Safety and Benefits of Fluoridation
Water fluoridation has generated less opposition in the United States than in
Europe. However, notwithstanding recommendations from many governmental and
professional health organizations, this practice continues to generate controversy in
some U.S. communities. Research gaps regarding the effects of long-term exposure
to increased levels of fluoride fuel this debate, and decades into this practice, the
safety and efficacy of water fluoridation continues to be questioned, debated, and
studied.
Dental Fluorosis. Some oppose water fluoridation because of a concern that
even recommended “optimal” levels of fluoridation may cause some dental fluorosis
in children. Dental fluorosis is caused by excessive fluoride intake while teeth are
developing, and it is during this period before teeth erupt that dental tissues are very
sensitive to fluoride (typically during a child’s first eight years).¹⁶ Mild dental
fluorosis is characterized by opaque white or stained patches in the dental enamel.
More severe fluorosis is characterized by pitting of tooth enamel. Since the 1960s,
the U.S. Public Health Service has recommended an “optimal” fluoride concentration
in water of 0.7 to 1.2 mg/L. This level was designed to “maximize prevention of
caries while limiting the prevalence of dental fluorosis to about 10% of the
population, virtually all of it mild to very mild.”¹⁷
Because of the increased use of fluoridated dental products and the tendency for
young children to swallow these products, concern over dental fluorosis and other
potential effects of fluoride ingestion has increased. Questions have arisen as to
whether current fluoridation practices and levels offer the most appropriate ways to
provide the expected beneficial effects of fluoride while avoiding adverse effects that
can result from ingesting too much fluoride. As noted by the National Research
Council (NRC) of the National Academy of Sciences in 1997,
In addition to fluoride in drinking water, people also can ingest fluoride in
toothpaste, mouth rinse, and dietary fluoride supplements or in beverages and
foods prepared with fluoridated water. As a result, many Americans might ingest
more “incidental” fluoride than was anticipated by the PHS [Public Health¹⁸

Service] and by EPA in recommending standards for drinking water.
¹⁶ Institute of Medicine. Dietary Reference Intakes for Calcium, Phosphorus, Magnesium,
Vitamin D, and Fluoride, Standing Committee on the Scientific Evaluation of Dietary
Reference Intakes, Food and Nutrition Board, National Academy Press, 1997, p. 298.
¹⁷ National Research Council, Health Effects of Ingested Fluoride, Subcommittee on Health
Effects of Ingested Fluoride, Committee on Toxicology, Board on Environmental Studies
and Toxicology, Commission on Life Sciences, National Academy Press, 1993, p. 5.
Researchers determined that dental fluorosis had a clear dose-response relationship —
increasing in severity and prevalence at higher concentrations. In 1993, the NRC estimated
that the effects generally ranged from mild or very mild, occurring at roughly 0.7 to 1.0
mg/L, to pronounced discoloration and pitting of teeth, occurring at 5 to 7 mg/L and higher.
¹⁸ Ibid.

According to a 2002 study, fluorosis prevalence among schoolchildren in the
1980s ranged from 18% to 26%, depending on the analytical index used. The authors
further estimated that approximately 2% of U.S. schoolchildren may experience
“perceived esthetic problems” that could be attributable to currently recommended
levels of fluoride in drinking water combined with fluoride toothpaste consumption.¹⁹
However, the authors noted that data were not available for other potential fluoride
exposures resulting from the ingestion of fluoridated toothpaste and diluted infant
formula consumption, and that, consequently, the risk of fluorosis attributable to
fluoridation of public water supplies may be overestimated if fluoride consumption
was higher in fluoridated areas.²⁰ The researchers concluded that in determining the
optimal fluoridation policy, the prevalence of dental fluorosis
should be weighed against fluoridation’s lifetime benefits and the feasibility and
associated costs of alternative solutions such as educating parents of preschoolers
about appropriate toothpaste use and lowering the current fluoride content of
children’s toothpaste. Given that fluorosis results from fluoride exposure during
a narrow age range and that the benefits accrue over the entire life span,
educating parents as to the appropriate use of fluoride toothpaste or reducing the
fluoride content of children’s toothpaste as some have suggested may be more²¹
efficient than altering current fluoridation policy.
In its 1993 fluoride health effects report, the NRC agreed with this conclusion
in principle, but determined that this approach may not be feasible in practice:
The most effective approach to stabilizing the prevalence and severity of dental
fluorosis, without jeopardizing the benefits to oral health, is likely to come from
more judicious control of fluoride in foods, processed beverages, and dental
products, rather than a reduction in the recommended concentrations of fluoride
in drinking water. But applying such a policy would be formidable; reduction of
fluoride concentrations in drinking water would be easier to administer, monitor,²²
and evaluate.
Although mild to moderate dental fluorosis had been considered by agencies to
be a cosmetic effect, not a health effect, it may be objectionable to many and, if
severe enough, may adversely affect tooth health. Therefore, this issue has factored
in the fluoridation debate.²³

¹⁹ Griffin, Susan O., Eugenio D. Beltran, Stuart A. Lockwood, and Laurie K. Barker,
Esthetically Objectionable Fluorosis Attributable to Water Fluoridation, Community Dental
Oral Epidemiology, 2002, vol. 30, pp. 199-209. The prevalence of “perceived esthetic
problems” was assessed by evaluating fluorosis in the teeth at the front of the mouth.
²⁰ Ibid. pp. 199, 208-209.
²¹ Ibid. p. 209.
²² National Research Council, Health Effects of Ingested Fluoride, 1993, pp. 47-48.
²³ In setting a standard for fluoride in drinking water, EPA considered dental fluorosis to be
a cosmetic effect, not an adverse health effect, and set the standard at a level that was not
intended to protect against mild dental fluorosis. This issue is discussed below in the section
on the federal regulation of fluoride in drinking water.

In response to the widespread use of bottled waters and availability of a variety
of fluoride-containing products, the CDC issued new recommendations for fluoride
use in 2001. The recommendations are intended to guide health-care providers and
the public on the appropriate use of fluoride from various sources (such as tooth paste
and baby formula made with fluoridated water). The recommendations specifically
address fluoride intake among children aged younger than six years to decrease the
risk for enamel fluorosis.²⁴ The CDC also suggested areas for further research.
Similarly, in 2006, the American Dental Association issued interim guidance
on infant formula and fluoride. While affirming its support for fluoridation, the ADA
recommended that infant formulas be mixed with water that is fluoride free or has
very low levels of fluoride to decrease the risk of dental fluorosis.²⁵
Health Effects. Researchers continue to study the potential health effects
associated with exposure to fluoride in drinking water. Many of the studies have
focused on ingestion of higher, naturally occurring levels of fluoride rather than on
artificial fluoridation levels. The studies generally have shown that fluoride ingestion
at elevated levels primarily produces effects on skeletal tissues (skeletal fluorosis)
and that these effects are more severe as exposure to fluoride increases above a
threshold. Very mild, skeletal fluorosis is characterized by slight increases in bone
mass. The most severe form of this condition, “crippling skeletal fluorosis,” involves
bone deformities, calcification of ligaments, pain, and immobility. In 1993, the NRC
reported that few cases of this condition had been reported in the United States and
that it was not considered a public health concern.²⁶
Bone Fracture Incidence. A related question that has been the subject of
scientific research concerns whether artificial water fluoridation increases the risk of
bone fracture in older women. A number of community-level studies conducted in
the 1980s and 1990s compared rates of fracture, specific for age and gender, between
fluoridated and nonfluoridated communities. Several of these studies indicated that
exposure to fluoridated water increased the risk of fracture, a few studies indicated

²⁴ Centers for Disease Control and Prevention, “Recommendations for Using Fluoride to
Prevent and Control Dental Caries in the United States,” Morbidity and Mortality Weekly
Report, vol. 50, no. 14, August 17, 2001, pp. 1-42. Available online at [http://www.cdc.gov/
fluoridation/guidelines/tooth_decay.htm]. The CDC recommendations included 1) using
alternate water sources for children eight years and younger if the primary drinking water
source has naturally occurring fluoride above 2 mg/L; 2) seeking professional advice on the
use of fluoride toothpaste for children younger than two years; 3) supervising tooth brushing
for children younger than age 6; 4) prescribing fluoride supplements judiciously; and 5)
using fluoride mouth rinses appropriately.
²⁵ American Dental Association, Fluoride and Fluoridation: Infants, Fluoride, and Bottled
Water. November 2006, [http://www.ada.org/public/topics/fluoride/index.asp#emerging].
²⁶ National Research Council, Health Effects of Ingested Fluoride, 1993, p. 59. The severity
of fluorosis varies among individuals and is complicated by factors such as malnutrition,
calcium deficiency, and impaired kidney function (the kidneys clear much of the fluoride
that is ingested). India has a high incidence of fluorosis because water supplies in large
areas of the country contain high levels of naturally occurring fluoride. Fluorosis is also
widely prevalent in China, the Middle East, North Africa, and other parts of Africa.

that water fluoridation reduced the risk of fracture, and several studies found no
effect.²⁷ However, a weakness of these studies was that they were based on
community-level data and lacked data on individuals.
To improve understanding of this issue, a 2000 study looked at the consumption
of fluoridated water and fractures in individual women. The results of this study
suggested that water fluoridation may reduce the risk of fractures of the hip and
vertebrae in older white women (the subjects of the study).²⁸
Cancer studies. A possible link asserted in the 1970s between water
fluoridation and increased cancer mortality raised health concerns and heightened
controversy over the practice of fluoridation. Some researchers had reported that
cancer mortality was higher in areas with fluoridated drinking water than in
nonfluoridated areas.²⁹ These findings were refuted subsequently by other³⁰
investigators who identified problems with the study’s research methodology.
However, because of the importance of this question, researchers have continued to
examine the possibility of an association between artificially fluoridated water and
cancer in humans.
Independent expert panels conducted reviews of the available scientific studies
in 1982 and 1985. The panels concluded that the studies provided “no credible
evidence for an association between fluoride in drinking water and risk of cancer.”³¹
However, according to the 1993 NRC fluoride review, all but one of these studies
were ecological studies; that is, they were either geographic correlation or time-line
studies that looked at exposures at the community level rather than individual
exposures.³² Consequently, the interpretation of the data was limited by an inability
to measure individual fluoride exposures over long periods of time, or to measure
exposure to other known risk factors such as smoking or other cancer-causing³³

substances.
²⁷ National Research Council, Health Effects of Ingested Fluoride, pp. 60-61.
²⁸ Phipps, Kathy R., Eric S. Orwoll, Jill D. Mason, Jane A. Cauley, “Community Water
Fluoridation, Bone Mineral Density, and Fractures: Prospective Study of Effects in Older
Women,” British Medical Journal, October 7, 2000, vol. 321, pp. 860-864.
²⁹ Yiamouyannis, J. and D. Burk, “Fluoridation and Cancer: Age Dependence of Cancer
Mortality Related to Artificial Fluoridation,” Fluoride, no. 10, 1977, pp. 102-123.
³⁰ National Research Council, Health Effects of Ingested Fluoride, 1993, p. 16.
³¹ Ibid. p. 110.
³² Epidemiological studies look for associations between the occurrence of disease and
exposure to known or suspected causes. In ecological studies, the unit of observation is the
population or community; the specific exposures of individuals are not assessed.
³³ U.S. Department of Health and Human Services, Public Health Service, Ad-hoc
Subcommittee on Fluoride, Committee to Coordinate Environmental Health and Related
Programs, Review of Fluoride: Benefits and Risks, Executive Summary, February 1991, p.

In another examination of this issue, scientists at the National Cancer Institute
(NCI) evaluated the relationship between drinking water fluoridation and the number
of cancer deaths in the United States by county. After examining more than 2.2
million cancer death records, NCI researchers concluded that “there was no
indication of increased cancer risk associated with fluoridated drinking water.”³⁴ The
NRC concluded in 1993 that “[t]he large number of epidemiological studies [more
than 50] combined with their lack of positive finding implies that if any link exists,
it must be very weak.”³⁵
In 1990, the National Toxicology Program (NTP) published the results of
studies on the potential carcinogenicity of fluoride in rats and mice.³⁶ The studies
found no evidence of carcinogenic activity in female rats or mice at very high
concentrations (100-175 mg/L) but found “equivocal evidence” of carcinogenicity
in male rats. Osteosarcomas (bone cancers) were observed in 1 of 50 male rats
receiving 100 mg/L sodium fluoride and 3 of 50 rats receiving 175 mg/L.³⁷ From this
study, NTP researchers concluded that levels of sodium fluoride below 175 mg/L in
drinking water over a two-year period would not be expected to cause any bone
cancers in rats or mice. The result of the NTP study (i.e., equivocal evidence of
carcinogenicity) was not confirmed in a 1992 study of rats using higher fluoride
doses; however, rare, nonmalignant tumors were found in this study.³⁸ According to
the Agency for Toxic Substances and Disease Registry, both studies had problems
that limited their usefulness in showing whether fluoride can cause cancer in
humans.³⁹
In response to the concerns raised by the NTP 1990 study, EPA requested that
the National Research Council (NRC) review the available toxicological and
exposure data on fluoride to determine whether the current drinking water standard
of 4 mg/L was sufficient to protect public health. In 1993, the NRC completed an
extensive literature review concerning the association between fluoridated drinking
water and increased cancer risk. Although the NRC concluded that the data did not
demonstrate an association between fluoridated drinking water and cancer, it did

³⁴ National Cancer Institute, Cancer Facts: Fluoridated Water, 2000. Details discussed in
National Research Council, Health Effects of Ingested Fluoride, Carcinogenicity of
Fluoride. 1993, pp. 109-112.
³⁵ Ibid. p. 121.
³⁶ National Toxicology Program, Toxicology and Carcinogenesis Studies of Sodium Fluoride
in 344/N Rats and B6C3F1 Mice, Department of Health and Human Services, National
Institutes of Health, Technical Report 393, NIH Publ. No. 91-2848, 1990, p. 447.
³⁷ By NTP definition, equivocal evidence of carcinogenic activity is a category for uncertain
findings by studies that are interpreted as showing a marginal increase in cancers that may
be related to the administration of a chemical.
³⁸ National Toxicology Program, NTP Supplemental 2-Year Study of Sodium Fluoride in
Male F344 Rats, CAS No. 7681-49-4, Study No. C55221D, National Institute of
Environmental Health Sciences, Research Triangle Park, NC, 1992.
³⁹ Agency for Toxic Substances and Disease Registry, Toxicological Profile for Fluorides,
Hydrogen Fluoride, and Fluorine, U.S. Public Health Service, April 1993, p. 7.

suggest that more research should be undertaken (especially research that examined
individual, rather than population, exposures).⁴⁰
Toward this end, a 1995 case-control analysis of bone cancer in Wisconsin
controlled for several factors, including age at diagnosis. The researchers did not
observe an association between fluoridation at the time of diagnosis and bone cancer.
Although the study specifically examined young age groups (which some studies
suggest may be more sensitive to fluoride exposure), exposure assignments were
made without taking individual residence histories of the participants.⁴¹ Therefore,
the researchers did not account for duration or timing of exposure.
In 2002, EPA noted that new studies regarding the effects of fluoride on bone
had been published since the fluoride standard was promulgated in 1986, and that a
new analysis of the data was warranted. EPA again requested the NRC to review the
toxicological and epidemiological data on fluoride, to update the fluoride risk
assessment, and to evaluate the scientific basis and adequacy of EPA’s drinking
water standards for fluoride.⁴²
In March 2006, the NRC released Fluoride in Drinking Water: A Scientific
Review of EPA’s Standards.⁴³ Because the NRC committee’s charge was to evaluate
the adequacy of EPA drinking water standards, the NRC did not address questions
regarding the benefits or risks of artificial fluoridation. However, after reviewing the
available studies, the NRC committee concluded that “the evidence on the potential
of fluoride to initiate or promote cancers, particularly of the bone, is tentative and
mixed and that, overall, the literature does not clearly indicate that fluoride either is
or is not carcinogenic in humans.” The committee noted that the Harvard School of
Public Health was expected to publish a large hospital-based, case-control study of
osteosarcoma and fluoride exposure, and that the results of that study might help to
identify research needs. (The findings and recommendations of the NRC review are
discussed further in the “Regulation of Fluoride in Drinking Water” section below.)
Efficacy. The extent of the benefits of water fluoridation to oral health also has
received some scrutiny. An overall reduction in caries has been observed in both
fluoridated and nonfluoridated communities in the United States, and some more
recent studies have suggested that water fluoridation has become less important and
effective in preventing caries when compared with the findings of earlier studies.
Some of this research has attributed the smaller differences in caries prevalence

⁴⁰ National Research Council, Health Effects of Ingested Fluoride, pp. 121-123.
⁴¹ National Research Council, Fluoride in Drinking Water: A Scientific Review of EPA’s
Standards, Committee on Fluoride in Drinking Water, Board on Environmental Studies and
Toxicology, Division on Earth and Life Sciences, National Academies, March 2006.
⁴² U.S. Environmental Protection Agency, “National Primary Drinking Water Regulations:
EPA’s Review of Existing Drinking Water Standards and Request for Public Comment,” 67
Federal Register 19069, April 17, 2002.
⁴³ National Research Council, Fluoride in Drinking Water: A Scientific Review of EPA’s
Standards, Committee on Fluoride in Drinking Water, Board on Environmental Studies and
Toxicology, Division on Earth and Life Sciences, National Academies, March 2006, p. 8.

between fluoridated and nonfluoridated communities to the widespread use of
fluoride toothpaste and other preventive dental care, and to better nutrition.⁴⁴
Several studies, however, have suggested that the traditional measure of the
benefits of water fluoridation may understate its effectiveness. The authors of a 2001
study determined that the benefit of caries reduction from fluoridation is diffused to
adjacent nonfluoridated communities through the export of bottled beverages and
processed foods to those communities.⁴⁵ When this effect was accounted for, the
authors found a beneficial effect from water fluoridation that was closer to the
findings of studies conducted in the 1970s and earlier.⁴⁶ The results of a 1979-1980
survey found a 33% difference in the prevalence of dental caries among children in
fluoridated and nonfluoridated regions in the United States, whereas a 1986-1987
national survey identified an 18% difference in caries prevalence. The National
Institutes of Health (NIH) analyzed the 1986-1987 results and determined that when
the effect of topical fluoride was controlled, the difference between fluoridated and
nonfluoridated areas increased to 25%. According to the NIH researchers, the results
suggested that fluoridation continued to play a major role in the decline in caries.⁴⁷
In 2000, British researchers published the results of their systematic review of
214 studies on the safety and efficacy of water fluoridation. The researchers found
that water fluoridation was associated with an increased proportion of children
without caries and a reduction in the number of teeth with caries, but the overall
reductions were smaller than had been reported in earlier studies.⁴⁸ The review also
concluded that at a fluoride level of 1 mg/L, an estimated 12.5% of exposed
individuals would have fluorosis that could be considered aesthetically concerning.⁴⁹
In reviewing the 214 studies, the authors found no other adverse effects associated
with the fluoridation of drinking water. However, they noted that, overall, the studies
were of low to moderate quality and recommended better research.⁵⁰
Other Considerations. Aside from questions of safety and efficacy, social
and political concerns may influence decisions about water fluoridation. A central
issue for some who oppose fluoridation of the public water supply is lack of choice.

⁴⁴ See, for example, Seppa, L., et al. “Caries Occurrence in a Fluoridated and a
Nonfluoridated Town in Finland: A Retrospective Study Using Longitudinal Data from
Public Dental Records,” Caries Research, 2002, vol. 36, no. 5, pp. 308-314.
⁴⁵ Griffin, Susan O., Barbara F. Gooch, Stuart A. Lockwood, and Scott Tomar. “Quantifying
the Diffused Benefit from Water Fluoridation in the United States,” Community Dentistry
and Oral Epidemiology, 2001, vol. 29, pp. 120-129.
⁴⁶ Ibid. p. 128.
⁴⁷ Brunelle, J.A. and J.P. Carlos, “Recent Trends in Dental Caries in U.S. Children and the
Effect of Water Fluoridation,” National Institute of Dental Research National Institutes of
Health, Journal of Dental Research, February 1990, vol. 69, pp. 723-727.
⁴⁸ McDonagh, Marian S., Penny F. Whiting, et al., “Systematic Review of Water
Fluoridation,” British Medical Journal, October 7, 2000, vol. 321, pp. 855-864.
⁴⁹ Ibid. p. 855.
⁵⁰ Ibid. p. 859.

Consumers who prefer not to drink fluoridated water generally are unable to exercise
that choice without treating their tap water or buying bottled water. Some view a
state or community fluoridation requirement as intrusive and object to receiving
water that is not free of additives, other than those needed to make water safe. (In
contrast, disinfectants, such as chlorine, generally have been accepted as necessary
to protect public health by eliminating pathogens). In this view, decisions regarding
dental health-care practices should be made by individuals and families and not
imposed by the government.
To the extent that research gaps exist regarding potential adverse effects of
increased exposures to fluoride because of its presence in multiple sources (e.g.,
water, beverages, toothpaste and rinses), the conflict between individual choice and
public policy is likely to continue.
Regulation of Fluoride in Drinking Water
This section discusses the federal regulation of fluoride in drinking water to
protect against the potential adverse health effects associated with exposure to higher,
typically naturally occurring fluoride levels (compared with levels recommended for
artificial fluoridation to protect dental health). It reviews the current federal
standards for fluoride in drinking water, EPA’s steps to review and potentially revise
the standards, and the NRC’s updated assessment of the scientific basis of EPA’s
standards and the adequacy of those standards to protect public health.
Fluoride poses challenges to regulators because many communities intentionally
add it to their water supplies for a beneficial effect at low levels, whereas it has toxic
effects and is regulated as a drinking water contaminant when it occurs in public
water supplies at higher concentrations. Moreover, the range between the amounts
that are considered beneficial and excessive is narrower for fluoride than for many
trace minerals.⁵¹
Standard Setting. The Safe Drinking Water Act (SDWA) requires EPA to
promulgate national primary drinking water regulations for contaminants that may
pose health risks and that are likely to be present in public water supplies. For each
contaminant that EPA determines requires regulation, EPA sets a non-enforceable
maximum contaminant level goal (MCLG) at a level at which no known or
anticipated adverse health effects occur and that allows an adequate margin of safety.
Amendments in 1996 (P.L. 104-182) added a requirement that EPA also must
consider the exposure risks to sensitive subpopulations (e.g., children). Because
MCLGs are based only on health effects and not on the availability or cost of

⁵¹ Many trace minerals share the property of having a health benefit at low levels but toxicity
at higher levels (e.g., copper, chromium, manganese, selenium, and zinc). Although certain
amounts of fluoride help make tooth enamel resistant to caries, fluoride has not been
classified as an essential nutrient. In 1997, the National Academy of Science established
Dietary Reference Intakes (DRI) for fluoride as a nutrient. The DRI included age- and
gender-specific tolerable upper intake levels (UL) to indicate the highest average daily
intake level likely to pose no risk of adverse effect to most individuals. The NAS also
established Adequate Intake (AI) values for fluoride. AI values are set when the data do
not permit determination of a Recommended Dietary Allowance (RDA).

monitoring and treatment technologies, they may be set at levels that are not feasible
for water systems to meet. For example, EPA typically sets MCLGs for carcinogens
at zero. EPA also considers the relative contribution that drinking water is expected
to make to total human exposure to a contaminant. Under current policy, EPA
assumes that 80% of exposure comes from other sources, such as the diet, and EPA
sets a stricter MCLG to account for other sources of exposure.⁵²
Using the MCLG as a starting point, EPA then sets an enforceable standard, the
maximum contaminant level (MCL). The MCL generally must be set as close to the
MCLG as is “feasible” using the best technology or other means available, taking
costs into consideration. The MCL is the legal limit of the amount of a substance
that may be present in water provided by public water systems.
EPA also may issue secondary MCLs (SMCLs) that establish nonmandatory
water quality standards for substances. These secondary standards are established as
guidelines to help public water systems manage drinking water for aesthetic (e.g.,
taste and odor), cosmetic (e.g., tooth discoloration), and technical (e.g., corrosivity)
effects.
Fluoride Standards. EPA issued the current national primary drinking water
regulation for fluoride in 1986. This regulation included an MCLG and an
enforceable drinking water standard MCL of 4 mg/L, which is intended to protect⁵³
against fluoride’s effects on the bone (specifically, crippling skeletal fluorosis).
The promulgation of the 4 mg/L standard was controversial, as it replaced a stricter,
interim standard of 1.4 to 2.4 mg/L that was established in 1975 to protect against
objectionable (moderate) dental fluorosis, which EPA previously had considered an⁵⁴
adverse health effect. (By comparison, the World Health Organization guideline
for fluoride in drinking water is 1.5 mg/L.) When promulgating the new regulation,
EPA estimated that, nationwide, 282 public water systems serving roughly 184,000
people had fluoride levels that exceeded the new standard of 4 mg/L. More recently,
EPA has estimated that 220,000 people receive water from public water systems with
fluoride levels that equal or exceed 4 mg/L.

⁵² For a discussion of EPA’s standards revision approach, see U.S. EPA, Six-Year Review
Chemical Contaminants Health Effects Technical Support Document, EPA 822-R-03-008,
June 2003.
⁵³ 51 Federal Register 11396, April 2, 1986. Note: In 1986, MCLGs were known as
recommended MCLs (RMCLs) and EPA was required to issue RMCLs before setting
MCLs. EPA promulgated the fluoride RMCL November 14, 1985 (50 Fed. Reg. 47142).
⁵⁴ Ibid, p. 11410. The Office of Management and Budget had opposed EPA’s initial plan
to reaffirm the stricter standard. Also, in 1981, the state of South Carolina had brought suit
against EPA, arguing that the cost of complying with the stricter standard was prohibitive
and not justified by the benefits. In 1987, the Natural Resources Defense Council sued EPA
for relaxing the standard, but the Court of Appeals for the D.C. Circuit concluded that
substantial evidence in the record supported EPA’s determination that the MCLG provided
an adequate margin of safety. (Source: Letter to Ralph Nader from Rebecca Hanmer, EPA’s
Office of Water, November 2, 1987.)

When setting the fluoride MCL, EPA acknowledged that it would not protect
infants and young children against moderate dental fluorosis, which EPA considered
a cosmetic effect rather than an adverse health effect. Consequently, EPA established
a secondary standard for fluoride at a level of 2 mg/L to protect children against
dental fluorosis, as well as adverse health effects. (EPA standards for fluoride in
drinking water are outlined in Table 1.) The CDC estimates that 850,000 people are⁵⁵
served by water systems that contain more than 2 mg/L fluoride.
Table 1. EPA Standards for Fluoride in Drinking Water
St andard Def i ni t i on/ P urpose
Maximum Contaminant LevelThe level of a contaminant in drinking water below
Goal (MCLG): which there is no known or expected risk to health.

4 mg/LMCLGs allow for a margin of safety and are non-

enforceable public health goals.
National Primary DrinkingThe highest level of a contaminant that is allowed in
Water Standard (Maximumdrinking water. MCLs are legally enforceable
Contaminant Level [MCL]): standards that apply to public water systems. They are
4 mg/Lset as close to MCLGs as feasible using the best
treatment technology available (taking cost into
consideration).
National Secondary DrinkingSMCLs are non-enforceable guidelines for
Water Standard (SMCL):contaminants in drinking water that may cause
2 mg/Lcosmetic effects (e.g., tooth discoloration, as in the
case of fluoride) or aesthetic effects (e.g., taste and
odor). EPA recommends SMCLs to public water
systems but does not require systems to comply. States
may choose to adopt them as enforceable standards.
Because of concerns regarding dental fluorosis, EPA does not recommend that
infants consume water containing 4 mg/L fluoride. The fluoride regulation requires
public water systems with water containing more than 2 mg/L fluoride to notify their
customers and inform them that alternate sources of water should be used for infants
and children (40 CFR 143.5). However, EPA allows water systems one year to notify
customers when the secondary standard is exceeded. This notification lag has been
criticized because infants and children can have sustained exposure to elevated
fluoride levels during a critical period of tooth development.
The Safe Drinking Water Act requires EPA to review and revise, as appropriate,
each drinking water regulation at least every six years. Any revision must maintain
or provide for greater protection of human health (SDWA §1412(b)(9)). EPA has
initiated a review of the fluoride MCLG, MCL and SMCL to determine whether they
are adequately protective of public health, based on the currently available scientific
research.
EPA Fluoride Standards Review. Following increased concern regarding
the potential carcinogenicity of fluoride related to the results of the 1990 NTP animal

⁵⁵ Unpublished data as reported in National Research Council, Fluoride in Drinking Water:
A Scientific Review of EPA’s Standards, 2006, p. 21.

study, EPA asked the NRC to review the available toxicological and exposure data
on fluoride, and to assess the sufficiency of the current drinking water standard. The
NRC had concluded in 1993 that the national primary drinking water standard for
fluoride (4 mg/L) was “appropriate as an interim standard” to protect public health.
However, the NRC noted that since EPA had promulgated the drinking water
regulation for fluoride in 1986, the use of fluoride in dental products had increased
and, as a result, many Americans might ingest more “incidental” fluoride than was
anticipated by the Public Health Service and by EPA when recommending standards
for drinking water.⁵⁶ Moreover, the NRC found inconsistencies in the fluoride
toxicity data base and gaps in knowledge, and it recommended further research in the
areas of fluoride intake, dental fluorosis, bone strength, and carcinogenicity. The
NRC further recommended that EPA’s fluoride standard should be reviewed and, if
necessary, revised when results of new research become available.⁵⁷
Toward that end, in 1998, EPA commissioned an evaluation of the exposure
data for fluoride, including data on amounts in water, foods, and dental products.
Moreover, in 2002, EPA published the results of its statutorily required review of
existing drinking water standards and noted that new studies on fluoride’s effects on
bone had been published since the fluoride standard was established in 1986. EPA’s
literature search had identified various reports on the clinical, toxicological, and
epidemiological data on fluoride and the skeletal system, and EPA concluded that a
review of the new data was justified as part of the regulatory review process.
Consequently, EPA asked the NRC to conduct a review of the data, to update the
fluoride health risk assessment, and to review EPA’s relative source contribution
assumptions for fluoride.⁵⁸ The NRC agreed to evaluate the scientific basis for EPA’s
MCLG and secondary fluoride standard, and to advise EPA on the adequacy of its
secondary standard to protect children and others from adverse effects.

2006 NRC Review of EPA’s Fluoride Standards:

Findings and Recommendations
In response to EPA’s request for a new data review, the National Research
Council convened the Committee on Fluoride in Drinking Water to evaluate
toxicologic, epidemiologic, and clinical data on fluoride, with emphasis on data that
had become available since the NRC’s 1993 report. EPA also asked the committee
to evaluate the scientific basis and adequacy of EPA’s maximum contaminant level
goal (MCLG) and secondary standard for fluoride. ⁵⁹

⁵⁶ National Research Council, Health Effects of Ingested Fluoride, 1993, p. 2.
⁵⁷ Ibid., p. 11.
⁵⁸ EPA based the current standard on the assumption that drinking water was the only source
of fluoride exposure; thus, water’s relative source contribution was considered to be 100%.
⁵⁹ Because primary drinking water standards, MCLs, are based on several factors, including
health effects and toxicological data, monitoring and treatment technology capabilities,
costs, and policy judgments, the NRC focused its evaluation on the science-based MCLG
rather than on the MCL. In the case of fluoride, the MCLG and MCL are identical.

In March 2006, the NRC committee issued Fluoride in Drinking Water: A
Scientific Review of EPA’s Standards. The study concluded that EPA’s MCLG of
4 mg/L should be lowered, and that information gaps regarding fluoride “prevented
the committee from making some judgments about the safety or the risks of fluoride
at concentrations of 2 to 4 mg/L.”⁶⁰ (Because the NRC’s charge was to evaluate the
scientific basis and adequacy of EPA’s drinking water standards for fluoride, the
committee did not address questions concerning the risks or benefits of artificial
fluoridation.) The NRC committee’s major findings are reviewed below.
Dental Fluorosis. When EPA promulgated the fluoride regulation in 1986,
it did not differentiate between mild and severe dental fluorosis, and broadly
considered fluorosis of the dental enamel to be a cosmetic effect. In contrast, 10 of
the 12 NRC committee members concluded that severe enamel fluorosis is an
adverse health effect, not simply a cosmetic effect. The committee members
explained that severe enamel fluorosis involves enamel loss, and that loss
compromises the function of tooth enamel, the purpose of which is to protect the
tooth against decay and infection. Because severe enamel fluorosis occurs in roughly
10% of children in communities with water fluoride concentrations at or near the
current standard of 4 mg/L, the committee unanimously agreed that the MCLG
should be set to protect against this condition, and that EPA’s standard of 4 mg/L is⁶¹
not adequately protective.
Skeletal Fluorosis. As noted, EPA set the fluoride MCLG and MCL to
protect against the adverse health effect of crippling skeletal fluorosis (stage III
skeletal fluorosis). In this latest review, the NRC committee concluded that stage II
skeletal fluorosis, the symptoms of which include sporadic pain, joint stiffness, and
abnormal thickening (osteosclerosis) of the pelvis and spine, also constitutes an
adverse health effect. Based on comparison of bone ash concentrations of fluoride
and related evidence of skeletal fluorosis, the committee further found the data to
suggest that
[F]luoride at 2 or 4 mg/L might not protect all individuals from the adverse
stages of the condition. However, this comparison alone is not sufficient
evidence to conclude that individuals exposed to fluoride at those concentrations
are at risk of stage II skeletal fluorosis. There is little information in the
epidemiologic literature on the occurrence of stage II skeletal fluorosis in U.S.
residents, and stage III skeletal fluorosis appears to be a rare condition in the
United States. Therefore, more research is needed to clarify the relationship
between fluoride ingestion, fluoride concentrations in bone, and stage of skeletal⁶²
fluorosis before any firm conclusions can be drawn.
Bone Fractures. The committee also reviewed the few studies available for
evaluating bone fracture risks from exposure to fluoride at 2 to 4 mg/L or more. The

⁶⁰ National Research Council, Fluoride in Drinking Water, 2006, pp. 8-9.
⁶¹ Ibid, pp. 104-105. The NRC fluoride committee concluded that “... damage to teeth
caused by severe dental fluorosis is a toxic effect that is consistent with prevailing risk
assessment definitions of adverse health effects.” (Summary, p. 3.)
⁶² National Research Council, Fluoride in Drinking Water, 2006, p. 146.

NRC reported that clinical studies indicated an increased risk of nonvertebral bone
fracture and a slightly decreased risk of vertebral fractures in populations exposed to
fluoride at 4 mg/L. The consensus of the committee was that, under certain
conditions, fluoride can weaken bone and increase the risk of fractures. Moreover,
The majority of the committee concluded that lifetime exposure to fluoride at
drinking water concentrations of 4 mg/L or higher is likely to increase fracture
rates in the population, compared with exposure at 1 mg/L, particularly in some
susceptible demographic groups that are more prone to accumulate fluoride in
their bones. However, three of the 12 members judged that the evidence only
supported a conclusion that the MCLG might not be protective against bone
fracture.... [T]he committee finds that the available epidemiologic data for
assessing bone fracture risk in relation to fluoride exposure around 2 mg/L are
inadequate for drawing firm conclusions about the risk or safety of exposures at⁶³
that concentration.
Carcinogenicity. The NRC noted that the question of whether fluoride might
be associated with bone cancer continues to be debated and analyzed, and that further
research should be conducted. Most committee members held the view that the 1992
cancer bioassay that found no increase in osteosarcoma (a rare bone cancer) in male
rats lacked sufficient power to counter the overall evidence of a positive dose-
response trend found in the 1990 rat study.⁶⁴ After reviewing the studies available
to date, the NRC committee concluded that “the evidence on the potential of fluoride
to initiate or promote cancers, particularly of the bone, is tentative and mixed,” and
that, overall, the literature does not clearly indicate that fluoride either is or is not
carcinogenic in humans.⁶⁵ The NRC noted that the Harvard School of Public Health
was expected to publish a large, hospital-based case-control study of osteosarcoma
and fluoride exposure in 2006, and that the results of that study might help to identify
research needs. The NRC review did include an assessment of pre-publication data
from an exploratory analysis of a subset of the Harvard data that found an association
between exposure to fluoride in drinking water and the incidence of osteosarcoma in
young males. The authors of this research noted several limitations with the study and⁶⁶
concluded that further research was needed to confirm or refute the results.
Other Potential Effects. The NRC committee evaluated available scientific
studies that assessed a range of other possible health effects related to fluoride
exposure. This evaluation included a review of studies on fluoride’s potential
neurotoxicity and neurobehavioral effects, endocrine effects, and effects on the

⁶³ Ibid.
⁶⁴ Lack of statistical power generally is due to an insufficient number of observations (i.e.,
in this case, the number of rats).
⁶⁵ National Research Council, Fluoride in Drinking Water, 2006, p. 8, and pp. 274-284.
⁶⁶ Bassin, E.B., Wypij, D. Davis, R.B., Mittleman, M.A. Age-specific Fluoride Exposure
in Drinking Water and Osteosarcoma (United States), Cancer Causes and Control, 2006, v.
17, pp. 421-428. In a letter to the editor in this same issue, the principal investigator of the
larger 15-year Harvard research project, Dr. C. W. Douglass, cautioned readers not to over-
interpret the results of the Bassin study, and to wait for the results of the full study. The
results of the larger study have not yet been published.

gastrointestinal system, kidneys, liver, and immune system. Although various studies
in these areas suggested an association between fluoride exposure and adverse
effects, the committee generally concluded that the research on these topics was
insufficient to assess their significance. Overall, the committee noted that more
research was needed to determine what risks fluoride exposure at 4 mg/L might pose
in these areas.⁶⁷
Research Needs. Noting that research gaps prevented the NRC committee
from making certain judgments regarding the safety or risk of fluoride, the committee
made specific recommendations for further studies that the committee felt would help
fill data gaps and facilitate EPA’s revision of the fluoride standards. The
recommendations covered a wide range of topics, including exposure assessment,
pharmacokinetic studies, studies of enamel fluorosis, studies of stage II and stage III
skeletal fluorosis, bone fracture studies, and studies on other health effects (e.g.,⁶⁸
endocrine effects and brain function).
NRC Recommendations. Regarding the maximum contaminant level goal,
the NRC concluded that the MCLG of 4 mg/L should be lowered. The review
committee specifically recommended that
To develop an MCLG that is protective of severe enamel fluorosis, clinical stage
II skeletal fluorosis, and bone fractures, EPA should update the risk assessment
of fluoride to include new data on health risks and better estimates of total
exposure (relative source contribution) in individuals and to use current
approaches to quantifying risk, considering susceptible subpopulations, and⁶⁹
characterizing uncertainties and variability.
For the cosmetic effects-based secondary maximum contaminant level, the
committee noted that the current SMCL does not completely prevent the occurrence
of moderate enamel fluorosis. In 1986, EPA set the standard to keep the occurrence
of moderate enamel fluorosis to 15% or less of the exposed population. The
committee noted that, although this goal is being met, the degree to which moderate
enamel fluorosis might create an adverse psychological effect or an adverse effect on
social functioning is not known. The committee recommended additional research
on the prevalence and severity of enamel fluorosis in U.S. communities with fluoride
concentrations greater than 1 mg/L. Specifically,
The studies should focus on moderate and severe enamel fluorosis in relation to
caries and in relation to psychological, behavioral, and social effects among
affected children, among their parents, and among affected children after they⁷⁰

become adults.
⁶⁷ National Research Council, Fluoride in Drinking Water, 2006, p. 7.
⁶⁸ Ibid, p. 9-10.
⁶⁹ Ibid, p. 299.
⁷⁰ National Research Council, Fluoride in Drinking Water, 2006, p. 299.

Conclusion
Although the NRC’s new review of fluoride in drinking water did not address
questions of artificial fluoridation, the NRC did determine that EPA’s maximum
contaminant level goal for fluoride should be lowered. Assuming that a lower
MCLG would lead to a lower enforceable MCL, the NRC concluded that this would
prevent children from developing severe enamel fluorosis and reduce the lifetime
accumulation of fluoride in bone, which most committee members agreed “is likely
to put individuals at greater risk of bone fracture and possibly skeletal fluorosis.”⁷¹
Even if the NRC had confirmed EPA’s previous assessment of fluoride’s health
effects, the Agency still might revise the health-based primary standard and the
esthetics-based secondary standard. One reason for potential revisions is that when
EPA developed the current standards, the Agency considered drinking water to be the
only source of exposure for fluoride. Since then, sources of potential fluoride
exposure have increased, and now, when reviewing its standards, EPA would
consider fluoride intake from sources other than drinking water. This consideration
alone may lead to a lowering of the primary and secondary standards for fluoride. A
second reason that EPA might revise the standard is that the 1996 SDWA
amendments (P.L. 104-182) directed EPA to evaluate the effects of contaminants on
groups within the general population, such as children, that might be at greater risk
than the general population of adverse health effects due to exposure to contaminants
in drinking water.⁷²
Another possible revision to the fluoride regulation involves the public
notification requirements for the secondary standard. Dental fluorosis occurs while
tooth enamel is developing, and EPA has acknowledged that “waiting 12 months to
provide public notification may result in young children being exposed to high levels
of fluoride during the time at which they are most vulnerable.”⁷³ EPA has considered
revising the public notification requirements, but has not yet done so.
The NRC committee conducted an extensive review of the available science,
and EPA now has a significant foundation to support an update of its risk assessment
for fluoride. A revised risk assessment potentially could become the basis for a new,
more protective fluoride standard. However, in addition to health effects, EPA
considers compliance cost, risk reduction benefits, contaminant occurrence, technical
feasibility, and other factors when setting standards. Consequently, it remains to be
seen exactly how these factors, when taken together, might influence a new standard.
Although the purpose of the NRC study was to advise EPA on the adequacy of
its drinking water standards for fluoride, the evaluation of the available science is
likely to be of interest to those who are interested in evaluating the currently
recommended levels for water fluoridation, and to states and communities that are
assessing whether or not to fluoridate their public water supplies.

⁷¹ Ibid.
⁷² 42 U.S.C. 300g-1, SDWA Section 1412(b)(3).
⁷³ 67 Federal Register 19069, April 17, 2002.

Opposition to water fluoridation often has been driven by concerns about the
potential health risks of exposure to fluoride in drinking water; however, social and
political concerns also influence decisions about water fluoridation. A central issue
for some fluoridation opponents is lack of choice, and they oppose the addition of
any chemicals to the water supply other than those needed to make water safe. In
contrast, many public health professionals and government officials have held the
view that water fluoridation offers the most equitable and cost-effective way to
protect dental health across socially and economically diverse communities. The
conflict between individual liberty and social policy is one that is unlikely to be fully
resolved by more research. Additional scientific evidence can help inform the
decision to fluoridate a community’s water, but such choices often are not made
purely on the basis of science.
Because artificial fluoridation decisions have been made at the state and local
levels, Congress has not been at the forefront of the water fluoridation debate.
Nonetheless, Congress has expressed interest in water fluoridation issues in the past,
particularly as questions have arisen regarding the benefits and risks of this practice.
Since first enacted in 1974, the Safe Drinking Water Act (P.L. 93-523) has stated that
“[n]o national primary drinking water regulation may require the addition of any
substance for preventive health care purposes unrelated to contamination of drinking
water.”⁷⁴
The NRC’s recent finding that EPA’s drinking water standards for fluoride
should be lowered to protect against adverse health effects may generate new
congressional oversight and legislative attention, as might any forthcoming research
results. Issues that might attract particular interest might include the health effects
research gaps identified by the NRC, and the status of EPA’s review and potential
revision of the fluoride standards under the Safe Drinking Water Act.

⁷⁴ Safe Drinking Water Act, §1412(b)(11); 42 U.S.C. 300g-1.