The New York Times
March 13, 1990
Rat Study Reignites Dispute On Fluoride
by Malcolm W. Brown
A long-smoldering dispute over the safety of fluoridating public
water supplies has flared anew, forcing the nation's top health
officials to reevaluate the risks and benefits of using fluorides
to reduce tooth decay.
The latest review was triggered by a Congressionally mandated study
that recently reported evidence that high
doses of fluoride may cause cancer in rats. The study was carried
out by the National Toxicology Program,
the Federal Government's top agency for evaluating chemical risks.
The findings, though preliminary, dismayed
many health experts who have long felt, and still do, that the benefits
of fluoridation were substantial and that the risks of ingesting
the small amount of fluoride in water were slight.
The Department of Health and Human Services has scheduled a public
meeting on April 26 in Research Triangle Park, N.C., at which a
panel of outside experts will discuss and evaluate the fluoride
study.
Dr. David G. Hoel, acting director of the department's National
Institute of Environmental Health Sciences, said, ''After 45 years
of water fluoridation involving scores of human epidemiological
studies both in the United States and in other countries there has
not been any evidence that shows a relationship between fluoridation
and cancer or other diseases in humans.'' He added that the higher
incidence of cancer in fluoride-dosed rats ''could be the result
of chance alone.''
But worried representatives of the American Dental Association,
the National Institute for Dental Research, the Federal Centers
for Disease Control and other medical groups conferred on the report
at a special session of the International Association for Dental
Research in Cincinnati last week. Some of the discussion centered
on the effect the report was likely to have on public confidence
in fluoridation, and some participants predicted that it might be
serious.
Speakers did not challenge the report's data, but most of them
cautioned against interpreting the study as implying a hazard to
health. The Surgeon General's office announced the establishment
of a panel to evaluate the report. It will be headed by Dr. Frank
Young, former Commissioner of the Food and Drug Administration.
Health officials are hastening to reassure the public that the
results of the recent study do not imply a hazard to human beings
from fluoridated drinking water. They say that people consume far
lower doses of fluoride than did the test rats and that a single
animal test, no matter how well done, is not conclusive because
the results could well be due to chance. But opponents of fluoridation
say the study proves that reexamination of the safety of fluoridation
is warranted.
The data in the study by the National Toxicology Program, a branch
of the National Institute of Environmental Health Sciences, showed
that the incidence of bone cancer in male rats increased with increasing
doses of sodium fluoride, the compound used in fluoridating public
water supplies. Among 50 male rats who received a medium dose of
flouride, at 45 parts per million, one got bone cancer. Among 80
male rats given the highest dose of fluoride, at 79 parts per million,
four developed bone cancers. Both doses were well above the levels
found in drinking water. None of the female rats and none of the
mice got the bone cancer.
Previous animal tests suggesting that water fluoridation might
pose risks to humans have been widely discounted as technically
flawed. But the latest investigation was very careful to weed out
sources of experimental or statistical error, many scientists say,
and the results cannot be dismissed.
Dr. Edward Groth 3d, a biologist serving as associate technical
director of Consumers Union, said that many fluoride investigations
have purported to show a risk associated with fluoridation, but
that all had been challenged more or less successfully. ''The importance
of this study by the National Toxicology Program is that it is the
first fluoride bioassay giving positive results in which the latest
state-of-the-art procedures have been rigorously applied,'' he said.
''It has to be considered seriously.''
The new report disclosed that besides a higher bone cancer rate
in male rats, the effects of high fluoride doses also included an
increased incidence of mouth cancer in male and female rats. An
almost identical study using mice in place of rats, however, produced
no increase in these types of cancer. But one analyst said both
mice and rats incurred a rare form of liver cancer more often at
the higher doses.
The investigation has been termed by many experts as ''equivocal,''
partly because the effects of fluoride on mice differed so sharply
from those on rats. The results in rats could well be due to chance
or to some peculiarity in rats that is not found in humans, some
experts say.
The fluoridation of drinking water to prevent cavities began in
Grand Rapids, Mich., in 1945; today, roughly half of all Americans
drink fluoridated water. Most public health experts agree with an
estimate by the American Dental Association that tooth decay in
the United States, on average, has declined by up to 40 percent
since 1970, although some disagree that fluoridation is the reason.
Most health experts also say that fluoridation is essentially harmless
to human beings, but a small minority has always believed that it
poses unacceptable risks. The latest study has reinforced this view
and rekindled questions about the advisability of fluoridation.
Disclosure Called Premature
The Lancet, the British medical journal, commented that even though
rats, rather than people, were used in the new study, ''large-dose
animal carcinogenicity tests have often been right on the money.''
The Lancet also found worrisome the fact that many high-dose rats
exhibited fluorosis (staining, pitting and embrittlement) of the
teeth and osteosclerosis (unhealthy hardening and growth of fibrous
tissue) of the long bones.
The Department of Health and Human Services was annoyed that its
subsidiary, the National Toxicology Program, had disclosed results
of the investigation; Dr. Hoel of the National Institute of Environmental
Health Sciences, called the disclosure ''premature'' and ''unanalyzed.''
A department spokesman, James Brown, said the scientists who conducted
the investigation would not be available for questions until the
April 26 meeting.
Even before the meeting, Dr. John A. Yiamouyiannis of Delaware,
Ohio, whose challenge to fluoridation on scientific grounds forced
the Public Health Service to undertake the fluoride investigation,
said: ''An in-depth analysis of the National Toxicology Program
study shows that the cancer-causing potential of fluoride is not
limited to one type of cancer. The main point is that fluoride is
a carcinogen.''
Most of the investigations of fluoride carcinogenicity have been
carried out using animals. Others, designed to determine whether
fluorides are mutagens, substances
tending to alter the genes of cells and therefore potential carcinogens,
have also been carried out on vegetables. Critics have argued that
these results cannot be translated into human risk.
Dr. Yiamouyiannis's role in the controversy received national attention
in 1977. He and Dr. Dean Burk, former head of the cellular chemistry
section of the National Cancer Institute, conducted a survey that
they said showed that fluoridation of water caused 10,000 excess
cancer deaths a year in the United States.
This conclusion was questioned by leaders of most public health
organizations, but subsequent hearings convinced Congress that the
Youmouyiannis-Burk study merited investigation. Congress ordered
the National Cancer Institute to arrange for appropriate animal
tests of fluoride toxicity and to conclude the study within three
years.
In fact, the investigation began only in 1980, and its initial
efforts failed because of the deaths of most of the control animals,
those that consumed no fluorides. A scientist familiar with the
study said the animals apparently died of malnutrition; the removal
of all fluorides from their food apparently removed some essential
nutrients as well, and they starved. Subsequently, laboratory procedures
were refined, and the test program resumed two years ago.
Preliminary results, which include complete tabular data on the
pathological condition of each of the hundreds of experimental animals,
completely vindicates his assertions, Dr. Yiamouyiannis said.
A slightly different view was expressed by Dr. Groth of Consumers
Union.
''The entire fluoridation controversy was colored from the outset
by stereotypical images of all opponents as zealots,'' he said.
''The movie 'Dr. Strangelove,' for instance, helped to create the
stereotype. In it, a crackpot general who opposes fluoridation goes
on to start World War III.'
'I Completely Disagree'
Dr. Groth said he mistrusts zealots of all kinds, but, regarding
the latest fluoridation study, added, ''The point is that this is
a legitimate scientific controversy. Proponents of fluoridation
insist that there are no grounds for controversy at all, and with
that, I completely disagree.''
Dr. Groth said that even the contention that fluorides are responsible
for reduction of tooth decay is open to question. ''There is hardly
any water fluoridation in Europe at all, except in Great Britain,''
he said, ''but tooth decay is nevertheless declining in Europe as
well. It may be that improved diets and living habits rather than
fluoridated water are responsible.''
At the Cincinnati meeting last week, Paul Slovik, an opinion analyst
from Eugene, Ore., predicted that most Americans will probably continue
to accept a possible small risk from water fluoridation if they
believe that the benefit is substantial. But if the benefits are
less than has been widely assumed, support is likely to weaken,
he said.
Sodium fluoride is a potent poison according to the Merck Index,
the leading compendium of the properties of chemical compounds.
Eating one gram of sodium fluoride can cause severe illness, and
a dose of five to ten grams (less than a half ounce) is fatal. However,
only about one part per million is used to fluoridate drinking water,
and even if the level is increased to four parts per million, the
advisable maximum, most experts believe the health risk is negligible.
To consume one gram of fluoride by drinking water that has been
fluoridated to a level of one part per million, a person would have
to drink more than 260 gallons. The rats and mice in the National
Toxicology study drank water containing fluoride at levels up
to 79 parts per million.
Still, the existence of low-dose risk to human beings may never
be proved or disproved. In light of the uncertainty, critics argue
that administrative bodies are unjustified in imposing fluoridation
on communities without obtaining public consent.
''The real issue here is not just the scientific debate,'' Dr.
Groth said. ''The question is whether any establishment has the
right to decide that benefits outweigh risks and impose involuntary
medication on an entire population. In the case of fluoridation,
the dental establishment has made opposition to fluoridation seem
intellectually disreputable. Some people regard that as tyranny.''
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