EPA Standard for Fluoride in Drinking Water
Is Not
Protective Tooth Enamel Loss, Bone Fractures of Concern at High Levels
Courtesy of www.epa.gov
WASHINGTON -- The U.S. Environmental Protection Agency's standard for
the maximum amount of fluoride allowed in drinking water -- 4 milligrams
of fluoride per liter of water -- does not protect against adverse health
effects, says a new report from the National Academies' National Research
Council. According to the most recent data, just over 200,000 Americans
have drinking water sources containing fluoride levels at 4 mg/L or higher.
The committee that wrote the report concluded that children exposed to
the current maximum allowable concentration risk developing severe tooth
enamel fluorosis, a condition characterized by discoloration, enamel
loss, and pitting of the teeth. A majority of the committee also concluded
that people who consume water containing that much fluoride over a lifetime
are likely at increased risk for bone fractures.
The report does not examine the health risks or benefits of the artificially
fluoridated water that millions of Americans drink, which contains 0.7
to 1.2 mg/L of fluoride. Although many municipalities add fluoride to
drinking water for dental health purposes, certain communities' water
supplies or individual wells contain higher amounts of naturally occurring
fluoride; industrial pollution can also contribute to fluoride levels
in water. Because high amounts of fluoride can be toxic, EPA places a
cap, or maximum contaminant level, on fluoride concentrations in drinking
water in order to prevent adverse health effects.
Although the agency's current maximum contaminant level for fluoride
in drinking water is 4 mg/L, a so-called secondary level of 2 mg/L was
set by EPA to protect against cosmetic dental effects linked to excess
fluoride consumption. According to the most recent data, about 1.4 million
people have water with 2 mg/L of fluoride.
In 1993 the Research Council reviewed EPA's maximum contaminant level
for fluoride and found it to be an appropriate interim standard until
further research was completed. Now that several more studies have been
done and because the Safe Drinking Water Act requires periodic reassessment
of regulations, EPA asked for a new review.
Most exposure to fluoride in the United States results from consumption
of water and water-based beverages, but dental products, food, and other
sources contribute as well. Highly exposed subpopulations include individuals
who have high concentrations of fluoride in their drinking water or who
drink more water than the average person because of exercise, outdoor
work, or a medical condition. Relative to their body weight, infants
and young children are exposed to three to four times as much fluoride
as adults. Children also may use more toothpaste than is advised or swallow
it, and many receive fluoride treatments from their dentists. Fluoride
accumulates in bone over time, so groups likely to have increased bone
fluoride concentrations include the elderly and people with severe renal
deficiency who have trouble excreting fluoride in their urine.
When assessing the risk for adverse health effects in populations with
water fluoride concentrations near the level of the EPA standards, the
committee assumed these populations had the same exposure to other sources
of fluoride as populations with smaller amounts of fluoride in their
water.
On average, approximately 10 percent of children in communities with
water fluoride concentrations at or near 4 mg/L develop severe tooth
enamel fluorosis, the new report says. Previous assessments have considered
all cases of enamel fluorosis, including serious ones, to be aesthetically
displeasing because of the yellow and brown staining of teeth that occurs,
but not adverse to health. However, the committee said that severe cases
of enamel loss constitute an adverse health effect because one function
of enamel is to protect the teeth and underlying dental tissue from decay
and infection. "The damage to teeth caused by severe enamel fluorosis
is a toxic effect that is consistent with prevailing risk assessment
definitions of adverse health effects," the committee reported.
Two of the 12 committee members did not agree that enamel defects alone
are sufficient to consider severe enamel fluorosis an adverse health
effect as opposed to a cosmetic one, but they did agree that EPA's maximum
contaminant level goal should be lowered to prevent the occurrence of
this unwanted condition.
Earlier studies indicate that up to 15 percent of children in communities
with 2 mg of fluoride per liter of water have moderate tooth enamel fluorosis.
Although this condition can also lead to tooth discoloration that may
be aesthetically objectionable, there is inadequate data to categorize
it as an adverse health effect.
Several studies indicate an increased risk of bone fracture in populations
exposed to fluoride concentrations in water of 4 mg/L or higher, the
committee added. Although fluoride increases bone density as it accumulates
in bone, there is evidence that under certain conditions it can weaken
bone and increase the risk of fractures. Most of the committee concluded
that a population with lifetime exposure to fluoride in water at concentrations
of 4 mg/L or higher is likely to experience more fractures than a group
exposed to 1 mg/L. Three of the 12 committee members, however, only supported
a conclusion that EPA's 4 mg/L limit might not be protective against
bone fractures; they said more evidence was needed before drawing a conclusion
that increased risk of fracture is likely. There was insufficient data
for the committee to reach any conclusions about fracture risk at the
2 mg/L level.
The report also looks at the risk of skeletal fluorosis, a bone and
joint condition associated with prolonged exposure to high concentrations
of fluoride. The most severe stage of skeletal fluorosis appears to be
rare in the United States, the committee noted. It also said that it
could not determine if earlier stages of the disease are occurring in
U.S. residents who drink water with fluoride at the 4 mg/L level, and
that more research is needed in this area.
The evidence to date regarding fluoride's potential to cause cancer,
particularly of the bone, is tentative and mixed, the committee added.
A study under way at the Harvard School of Dental Medicine, expected
to be published this summer, may help identify future research that would
be useful for studying fluoride's carcinogenic potential.
The committee's study was sponsored by the U.S. Environmental Protection
Agency. The National Research Council is the principal operating arm
of the National Academy of Sciences and the National Academy of Engineering.
It is a private, nonprofit institution that provides science and technology
advice under a congressional charter. A committee roster follows.
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