May 7, 1990
The Risks of Fluoride
The Long Awaited Verdict
by Sharon Begley
in Research Triangle Park, N.C.
If it were any other chemical, the news that fluoride may cause
cancer would probably have been greeted with little more than mutters
about the latest cancer causing substances of the week. But fluoride
is no ordinary chemical.
Added to public drinking water for 45 years in an effort to reduce
tooth decay, it has been a constant focus of impassioned, often
angry, debate, swirling around both political issues of "forced
medication" and scientific ones such as fluoridation's risks and
benefits.
Earlier this year, the National Toxicology
Program (NTP) released preliminary data from its most thorough
and detailed cancer test ever. The results showed that some rats
given fluoride in drinking water developed osteosarcomas,
rare bone cancers (NEWSWEEK, Feb. 5).
Last week, a panel of outside experts unanimously upheld that
conclusion, voting hat there is "equivocal"
evidence that fluoride causes cancer. "It's like there's a little
flashing yellow light on the instrument panel," said David Rall,
director of the National Institute of Environmental Health Sciences,
in Research Triangle Park, N.C., which oversaw the study. "It says
'you better look at this more carefully'."
"Equivocal" is the term applied when test animals display a marginal
increase in cancers that may be related to the chemical.
In the fluoride study, ordered by Congress in 1977, no mice or
female rats developed bone tumors. Neither did any of the male rats
drinking water containing 0 or 11 parts per million (ppm) fluoride.
But one rat on 45 ppm fluoride got osteosarcoma, as did three drinking
70 ppm water. Last week's panel stamped those results statistically
significant. Moreover, unlike other studies that "are often accused
of using doses thousands of times greater than [people get]," said
Rall, the fluoride levels the rats drank were not extreme. The legal
limit for fluoride in drinking water is 4 ppm; it is added to public
water supplies at about 1 ppm. More important, the level of fluoride
in the animals' bones -- the cancer site -- were about equal to
that seen in people who have consumed fluoridated water for many
years.
Human risk: Now public-health officials will consider other
evidence of fluoride's risks, as well as its benefits. Recent government
data show that tooth decay rates are 18 to 25 percent lower
in fluoridated than unfluoridated areas, far below the 60 percent
or more than proponents often claim. A panel of the U.S. Public
Health Service, the principal official promoter of fluoridation,
is planning to issue a report on the risks and benefits this July.
Its toughest challenge will be assessing evidence of human cancer
risk. Even the most sensitive epidemiological study of any substance
is lucky to detect a cancer rise of 10 to 15 percent; hardly anyone
says fluoride poses that great a threat.
Because of the difficulty of directly observing effects in humans,
many of the NTP reviewers emphasized the need to learn all we can
from test animals. Lauren Zeise of the California Department of
Health Services argued that NTP's animals could have withstood higher
fluoride doses; in a future study, that might more definitively
flush out the cancer risk. Ellen Silbergeld of the University of
Maryland, noting the lack of cancer in female rats, speculated that
females may sequester fluoride in their bones differently from males,
keeping it from living bone cells susceptible to carcinogens. Further
experiments might shed light on these sex differences.
Until such questions are resolved, the only certainty is that after
years in which the government and medical establishment maintained
that only quacks questioned fluoridation, the practice is once again
a subject for legitimate scientific debate.
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