It is one of the cardinal principles of pharmacology: “The poison is in the dose.” Thus, iodine is so important to health that tiny amounts are added to table salt, while a concentrated dose can kill you.
The principle can also be applied to a topic that has stirred controversy for 60 years: the fluoridation of public water supplies. A proposal before the state Legislature would mandate fluoridation for all public water systems serving more than 5,000 people.
There is general agreement that small amounts of fluoride can be effective at preventing dental decay. For over half a century, fluoride has been added to toothpaste, fluoride rinses have been distributed in schools and as a regular part of every dental exam.
More than one-third of Massachusetts cities and towns have fluoridated drinking water, including all of those served by the Massachusetts Water Resources Authority. Because it is in the public water supplies, fluoride also finds its way into many prepared foods and bottled drinks. Most people, especially children, are getting a good dose of fluoride every day.
There is also general agreement that fluoride, at high enough levels, is toxic. The chemical has been used as rat poison, and fluoridated toothpastes must include a warning telling people to call a poison control center if they swallow more than used for brushing.
The question is, what is the optimum dose? Are Massachusetts residents getting too little fluoride, too much, or just the right amount?
Fluoridation has always had its critics, some with a conspiratorial bent whose extreme tone undermined their credibility. But a growing chorus of critics is now being heard, some with impressive credentials and compelling data.
Critics now include a winner of the Nobel prize in medicine, one of Canada’s top dental researchers and 11 unions that represent 7,000 environmental and public health professionals at the U.S. Environmental Protection Agency. They point to evidence of an elevated risk of fatal bone cancer, to studies linking some fluoridation practices to increased levels of lead in the blood, to the presence of fluorosis, a usually mild condition that damages tooth enamel, in one out of three children.
The evidence is now in dispute, with the American Dental Association and several federal health agencies still strongly supportive of adding fluoride to drinking water. A new federal review of research on fluoride is expected to be released in February.
Fluoride has led to a dramatic reduction in tooth decay, but it is less clear how much of those gains can be attributed to the fluoridation of public drinking water. Scientists say fluoride is most effective when applied topically, as in toothpaste or a fluoride rinse, as opposed to ingesting it.
There are those who reject fluoridation on ideological grounds, objecting to “forced medication” no matter how benign. The practical issue is equally compelling: If we’re treating our teeth with fluoride, is it necessary to shower in it, wash our clothes with it, and water our lawns with it? And if some people are more susceptible to, say, fluorosis, why not let them decide how much fluoride to allow in their system?
Considering the large populations of people, over several generations, who have been exposed to fluoridated drinking water and the populations of people who have grown up in communities who don’t fluoridate or who get their water from private wells, it shouldn’t be difficult to obtain data on comparative rates of tooth decay, fluorosis, bone cancer or other health impacts.
We suggest the Legislature take a good, long look at that research before going any further with mandatory fluoridation.
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