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

Mary Tiemann
Specialist in Environmental Policy
January 3, 2011
Congressional Research Service
7-5700
www.crs.gov
RL33280
CRS Report for Congress
P
repared for Members and Committees of Congress
c11173008

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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 adds 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—a
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.
EPA currently is developing a dose-response assessment and updating the relative contribution
assessment for fluoride. Once these assessments have been completed and peer reviewed, EPA
will be able to determine whether revisions to the drinking water standards would be appropriate.

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

Contents
Introduction ................................................................................................................................ 1
Background ................................................................................................................................ 2
Questions About the Safety and Benefits of Fluoridation ............................................................. 4
Dental Fluorosis.................................................................................................................... 4
Health Effects ....................................................................................................................... 6
Bone Fracture Incidence.................................................................................................. 7
Cancer Studies ................................................................................................................ 7
Efficacy ................................................................................................................................ 9
Other Considerations........................................................................................................... 10
Regulation of Fluoride in Drinking Water.................................................................................. 11
Standard Setting.................................................................................................................. 11
Fluoride Standards .............................................................................................................. 12
EPA Fluoride Standards Review: 2002 ................................................................................ 13
EPA Fluoride Standards Review: 2010 ................................................................................ 14
2006 NRC Review of EPA’s Fluoride Standards: Findings and Recommendations ..................... 14
Dental Fluorosis.................................................................................................................. 14
Skeletal Fluorosis................................................................................................................ 15
Bone Fractures.................................................................................................................... 15
Carcinogenicity................................................................................................................... 16
Other Potential Effects ........................................................................................................ 16
Research Needs................................................................................................................... 16
NRC Recommendations ...................................................................................................... 17
Conclusion................................................................................................................................ 17

Tables
Table 1. EPA Standards for Fluoride in Drinking Water ............................................................. 12

Contacts
Author Contact Information ...................................................................................................... 19

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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, or 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
Academy of Sciences 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.
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Fluoride in Drinking Water: A Review of Fluoridation and Regulation Issues

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
The CDC considers the reduction in tooth decay from fluoridation one of the top public health
achievements of the 20th Century.6 In 2002, the CDC reported that
[d]uring the second half of the 20th 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 fluoride to the community.7
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

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 Public Health, 1900-1999: Fluoridation of Drinking
Water to Prevent Dental Caries,” Morbidity and Mortality Weekly Report, vol. 48, no. 41, October 22, 1999, pp. 933-
940. Available at http://www.cdc.gov/mmwr/preview/mmwrhtml/mm4841a1.htm.
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.
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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
prevalence of dental root caries would be expected to be higher in the absence of
fluoridation.11
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,
where water fluoridation may be a key factor in reducing inequalities in dental health.12
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 the optimal level.13 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

8 U.S. Department of Health and Human Services, Healthy People 2010—Understanding and Improving Health, 2nd
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 http://www.who.int/oral_health/
action/risks/en/index1.html.
11 Ibid.
12 World Health Organization, Naturally Occurring Hazards. Available at http://www.who.int/water_sanitation_health/
naturalhazards.html#fluoride.
13 British Fluoridation Society and the UK Public Health Association, One in a Million: The Facts about Water
Fluoridation
, 2nd ed., 2004, p. 71.
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(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
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

14 Mullen, J. History of Water Fluoridation, British Dental Journal, 2005. p. 1-4
15 Marthaler TM - “Salt fluoridation in Europe, comparisons with Latin America” 8th World Salt Symposium (2000);
Volume 2: 1021-1026 (2000).
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.
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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 NRC 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 Health Service] and by EPA in recommending standards for
drinking water.18
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 more efficient than altering current fluoridation policy.21
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, and evaluate.22

18 Ibid.
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.
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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
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

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.
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 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, Interim Guidance on Fluoride Intake for Infants and Young Children, November
2006, http://www.ada.org/1767.aspx.
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.
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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 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 other investigators
who identified problems with the study’s research methodology.30 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-causing substances.33

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. 9.
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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 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 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),

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.
40 National Research Council, Health Effects of Ingested Fluoride, pp. 121-123.
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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 additional 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 and
continues to do so. An overall reduction in caries has been observed in both fluoridated and
nonfluoridated communities in the United States and Canada, 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 between fluoridated and nonfluoridated communities to
the widespread use of fluoride toothpaste and other preventive dental care, and to better nutrition,
including higher intake of vitamin D.44
Several other studies 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

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.
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.
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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. 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.

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.
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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 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

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 Sciences
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).
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.
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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 protect against fluoride’s effects on the bone (specifically, crippling skeletal
fluorosis).53 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 an adverse health effect.54 (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.
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 are served by water systems that contain more than 2 mg/L fluoride.55
Table 1. EPA Standards for Fluoride in Drinking Water
Standard Definition/Purpose
Maximum Contaminant Level
The level of a contaminant in drinking water below which there is no known or expected
Goal (MCLG):
risk to health. MCLGs al ow for a margin of safety and are non-enforceable public health
4 mg/L
goals.
National Primary Drinking
The highest level of a contaminant that is allowed in drinking water. MCLs are legally
Water Standard (Maximum
enforceable standards that apply to public water systems. They are set as close to MCLGs
Contaminant Level (MCL)):
as feasible using the best treatment technology available (taking cost into consideration).
4 mg/L
National Secondary Drinking
SMCLs are non-enforceable guidelines for contaminants in drinking water that may cause
Water Standard (SMCL):
cosmetic effects (e.g., tooth discoloration, as in the case of fluoride) or aesthetic effects
2 mg/L
(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.

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.)
55 Unpublished data as reported in National Research Council, Fluoride in Drinking Water: A Scientific Review of
EPA’s Standards
, 2006, p. 21.
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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: 2002
Following increased concern regarding the potential carcinogenicity of fluoride related to the
results of the 1990 NTP animal 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 As
discussed below, 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.

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%.
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EPA Fluoride Standards Review: 2010
In March 2010, EPA announced the results of its review of drinking water regulations for 71
contaminants, including fluoride.59 Because of ongoing assessments, the agency concluded that a
revision to the fluoride regulation is not appropriate at this time. Specifically, the agency’s Office
of Water is developing a dose-response assessment of the noncancer impacts of fluoride on severe
dental fluorosis and skeletal systems. Additionally, the Office of Water is updating its evaluation
of the relative contribution of drinking water to total fluoride exposure, considering contributions
from dental products, foods, pesticide residues, and other potential sources.60 EPA intends to
complete and publish peer-reviewed versions of these assessments, and then determine whether
revisions to the MCLG, MCL, and/or SMCL would be appropriate.
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. 61
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.”62 (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

59 U.S. Environmental Protection Agency, “National Primary Drinking Water Regulations; Announcement of the
Results of EPA’s Review of Existing Drinking Water Standards and Request for Public Comment and/or Information
on Related Issues,” 75 Federal Register 1550, March 29, 2010.
60 Ibid., p. 15544.
61 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.
62 National Research Council, Fluoride in Drinking Water, 2006, pp. 8-9.
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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 is
not adequately protective.63
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 skeletal fluorosis
before any firm conclusions can be drawn.64
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 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 at that concentration.65

63 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.)
64 National Research Council, Fluoride in Drinking Water, 2006, p. 146.
65 Ibid.
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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.66 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.67 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 and concluded that further research was needed to confirm or refute the results.68
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 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.69
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

66 Lack of statistical power generally is due to an insufficient number of observations (i.e., in this case, the number of
rats).
67 National Research Council, Fluoride in Drinking Water, 2006, p. 8, and pp. 274-284.
68 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.
69 National Research Council, Fluoride in Drinking Water, 2006, p. 7.
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skeletal fluorosis, bone fracture studies, and studies on other health effects (e.g., endocrine effects
and brain function).70
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, and characterizing uncertainties and variability.71
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 they become adults.72
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.”73
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

70 Ibid., p. 9-10.
71 Ibid., p. 299.
72 National Research Council, Fluoride in Drinking Water, 2006, p. 299.
73 National Research Council, Fluoride in Drinking Water, 2006, p. 299.
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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.74
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.”75 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.
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.”76

74 42 U.S.C. 300g-1, SDWA Section 1412(b)(3).
75 67 Federal Register 19069, April 17, 2002.
76 Safe Drinking Water Act, §1412(b)(11); 42 U.S.C. 300g-1.
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The NRC’s 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.

Author Contact Information

Mary Tiemann

Specialist in Environmental Policy
mtiemann@crs.loc.gov, 7-5937


Congressional Research Service
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