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.”
*Original article online at https://www.nytimes.com/1990/03/13/science/rat-study-reignites-dispute-on-fluoride.html