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The Book

National Research Council
Recommends Fluoride Studies

Fluoride in Drinking Water:
A Scientific Review of EPA's Standards

Chapter 7: Neurotoxicity and Neurobehavioral Effects: Recommendations

Cover of NRC Report • On the basis of information largely derived from histological, chemical, and molecular studies, it is apparent that fluorides have the ability to interfere with the functions of the brain and the body by direct and indirect means. To determine the possible adverse effects of fluoride, additional data from both the experimental and the clinical sciences are needed.

• The possibility has been raised by the studies conducted in China that fluoride can lower intellectual abilities. Thus, studies of populations exposed to different concentrations of fluoride in drinking water should include measurements of reasoning ability, problem solving, IQ, and short-and long-term memory.

Studies of populations exposed to different concentrations of fluoride should be undertaken to evaluate neurochemical changes that may be associated with dementia. Consideration should be given to assessing effects from chronic exposure, effects that might be delayed or occur late-in-life, and individual susceptibility.

• Additional animal studies designed to evaluate reasoning are needed. These studies must be carefully designed to measure cognitive skills beyond rote learning or the acquisition of simple associations, and test environmentally relevant doses of fluoride.

• Most of the studies dealing with neural and behavioral responses have tested NaF. It is important to determine whether other forms of fluoride (e.g., silicofluorides) produce the same effects in animal models.

Chapter 8: Effects on the Endocrine System: Thyroid Function
• In particular, the inverse correlation between asymptomatic hypothyroidism in pregnant mothers and the IQ of the offspring is a cause for concern. The recent decline in iodine intake in the United States could contribute to increased toxicity of fluoride for some individuals.

Chapter 9: Effects on the Gastrointestinal, Renal, Hepatic, and Immune Systems: Renal and Hepatic Effects
• The effect of low doses of fluoride on kidney and liver enzyme functions in humans needs to be carefully documented in communities exposed to different concentrations of fluoride in drinking water.

Chapter 10: Genotoxicity and Carcinogenicity: Findings
• Fluoride appears to have the potential to initiate or promote cancers, particularly of the bone, but the evidence to date is tentative and mixed... Osteosarcoma is of particular concern as a potential effect of fluoride.

Genotoxicity: In vivo human genotoxicity studies in U.S. populations or other populations with nutritional and sociodemographic variables similar to those in the United States should be conducted. Documentation of subject enrollment with different fluoride concentrations would be useful for addressing the potential genotoxic hazards of fluoridated water in this country.

Chapter 11: Drinking Water Standards for Fluoride: Susceptible Subpopulations
• Individuals in need of special consideration include those who are particularly susceptible or vulnerable to the effects of fluoride. For example, children are vulnerable for developing enamel fluorosis, because the condition occurs only when there is exposure while teeth are being formed (the pre-eruption stages).

• The elderly are another population of concern because of their long-term accumulation of fluoride into their bones. There are also medical conditions that can make people more susceptible to the effects of fluoride.

Chapter 2: Measures of Exposure to Fluoride in the United States: Recommendations
• Fluoride should be included in nationwide biomonitoring surveys and nutritional studies. In particular, analysis of fluoride in blood and urine samples taken in these surveys would be valuable.

• To assist in estimating individual fluoride exposure from ingestion, manufacturers and producers should provide information on the fluoride content of commercial foods and beverages.

• Better characterization of exposure to fluoride is needed in epidemiology studies investigating potential effects. Important exposure aspects of such studies would include:

• collecting data on general dietary status and dietary factors that could influence exposure or effects, such as calcium, iodine, and aluminum intakes

• characterizing and grouping individuals by estimated total exposure, rather than by source of exposure, location of residence, fluoride concentration in drinking water.

Further analysis should be done of the concentrations of fluoride and various fluoride species or complexes (especially fluorosilicates and aluminofluorides) present in tap water, using a range of water samples (e.g., of different hardness and mineral content). Research also should include characterizing any changes in speciation that occur when tap water is used for various purposes – for example, to make acidic beverages.

The possibility of biological effects of hexafluorosilicate (SiF62), as opposed to free fluoride ion, should be examined.

Ten years after both the NRC and the National Scientific Council on the Developing Child emphasized the need for fluoride studies – especially for susceptible populations that include pregnant women and their fetuses – none had been conducted!

Therefore, at the urging of several organizations and over the objections of others, the National Toxicology Program began new studies to evaluate the effects of fluoridated water with respect to developmental neurobehavioral toxicity.