The case for fluoride

Mark Diesendorf proposes that chemicals in food and drink, in this instance fluoride, are a threat to both the natural environment and social equity. The article fails to acknowledge the considerable number of studies in recent years, several of them pivotal in terms of study design and adjustment for confounding factors, that have rigorously examined the effects of fluoride on human health. There is now overwhelming evidence that adding trace amounts of fluoride to water supplies has led to a dramatic decrease in the incidence of dental caries, particularly in children.

The strength and vitality of a society are vested in the opportunity for balanced and informed debate on issues of public concern, especially if it challenges an established practice or long-held belief. Society’s attitudes change, and new research can clarify issues of concern or point to other unforeseen consequences, as exemplified in our attitude to smoking and asbestos products, and the recent withdrawal of the antiarthritic drug Vioxx® from the Australian market.

Governments are charged with caring for the society they represent in a benign and cost-effective manner, and they have an obligation to consider carefully any recommendations from their expert committees prior to implementation. Public health programs are a balance between the benefit to society and the infringement of an individual’s rights, as illustrated by the examples of vaccines and chest X-rays. Similarly, water fluoridation provides dental health benefits to society in a cost-effective and socially equitable manner. It can be compared to the addition of vitamin D to margarine to maintain healthy bones, or folic acid to cereals to reduce the risk of pregnant women bearing children with spina bifida.

Fluoride occurs naturally in soil, water, plants and animals in trace quantities. It is the thirteenth most abundant element in the earth’s crust. Fluoride compounds in air rank third in air pollutants. Fluoride occurs naturally in all water supplies, mostly at levels too low to protect teeth from dental decay. It is present to some extent in most foods and drink. It is impossible to devise a fluoride-free diet.

Fluoride is not classified as a medication by medical authorities. In those communities with naturally fluoridated water it was observed that fluoride protected against tooth decay and that in some areas dental fluorosis occurred. Subsequent observation and experiment found that 1 ppm fluoride gave a balance between reduced decay and a minimal risk of mild dental fluorosis.

Fluoride is absorbed mostly from the stomach and small intestine and about half is then excreted in the urine. Most of the retained fluoride is taken up by bones and teeth. Very small amounts circulate in the blood and saliva and there is virtually none in other body tissues. The fluoride content of teeth reflects the biologically available fluoride at the time of tooth formation. After this time fluoride levels remain constant, except for the outermost layer of the enamel. This is important for two reasons. First, it means that at the time of tooth development only what was available after absorption can form part of the tooth structure. Once the tooth is formed no more fluoride is incorporated into it, but this does not apply to the enamel surface. Second, for enamel protection the tooth surface needs continuous bathing with fluoride.

Decay was previously thought to be prevented by incorporation of fluoride into the tooth enamel during formation. It is now known that decay prevention occurs on the surface of the tooth. Fluoride can be leached from the tooth surface as liquids pass over it, so it is important to protect erupted teeth by maintaining fluoride levels at the enamel surface. The presence of fluoride in plaque and saliva aids remineralisation of the enamel lesions before cavities become permanent. In this way it benefits both children and adults.

In erupted teeth, there is no doubt that the action of fluoride is essentially topical “surface ion exchange”, whereby the fluoride ion exchanges with the isostructural hydroxide ion present in the hydroxyapatite biomineral in teeth (and bone) to strengthen enamel and promote the remineralisation of microcavities, which form on teeth every day.

Certainly, ingestion leads to systemically absorbed fluoride, which can bathe the teeth as it is recycled in saliva - this not only ensures protection of the enamel, but also acts on cementum at the base of the tooth as gum shrinkage occurs. In older people, fluoride helps reduce the incidence of root surface decay as the surface becomes exposed to oral bacteria when the gums shrink. It also reduces the incidence of decay of the crown of the tooth. This is significant for the health of adults and, especially, aged people, because the single most important factor in maintaining health of the aged is good dental health for adequate nutrition.

The health concerns raised in Diesendorf’s article regarding fluorosis, bone effects, mental acuity and so on, have been reviewed extensively and exhaustively in our recent document commissioned by the National Health and Medical Research Council (NHMRC) in 1999. In that instance, an independent expert group of toxicologists, chemists, pharmacologists and epidemiologists concluded, on the basis of current information, that there were no unforseen consequences that might arise from fluoride exposure at the nominal 1 ppm level in drinking water. The evidence indicated that the current levels of fluoride added to drinking water supplies throughout Australia did not need altering (from the current 1.1 ppm in temperate Hobart to 0.6 ppm in subtropical Darwin, allowing for different water intake depending on climate).

Since then, several other groups have reported extensive studies and made similar conclusions based on new evidence. The author’s interpretation of the negative health effects of fluoride listed in the Table in his article is at odds with the numerous peer-reviewed journal articles in the literature. References to websites are of little value unless their validity can be established by independent peer review. It should also be noted that the NHMRC review The Effectiveness of Water Fluoridation explicitly examined the author’s claims about fluoride.

It is public knowledge that fluoride, like any other chemical, including vitamins and iron tablets, is a poison at high doses. The fatal dose for a 70 kg adult is equivalent to drinking about 2500 litres of optimally fluoridated water. Toxic effects may occur at moderate levels of exposure.