Fluoride Action Network

Southampton: Response to Bazian critique of NRC 2006 Fluoride Toxicology Review

Source: Fluoride Action Network | Director of Scientific Research, Fluoride Action Network (A project of the American Environmental Health Studies Project)
Posted on February 26th, 2009
Location: United Kingdom, England

February 26, 2009. Letter to:

South Central Strategic Health Authority (SHA)
Rivergate House, Newbury Business Park
London Road
Newbury, Berkshire RG14 2PZ UK

Via email

To: Dr Geoffrey Harris, Chairman, and Board Members,

Response to Bazian critique of NRC 2006 Fluoride Toxicology Review

Bazian Ltd. was contracted by SHA to critique the US National Research Council (NRC) 2006 review of the toxicity of fluoride. The critique is unsigned and was submitted to SHA after public comment was closed and one week prior to the decision on the fluoridation of 200,000 people.

The Bazian critique has mischaracterized the purpose, methods, and results of the NRC 2006 review. The NRC 2006 review was never intended to address the effectiveness question of water fluoridation, but only the safety question of fluoride in drinking water. The NRC review used the established methods of risk assessment, exposure assessment and toxicology to address the safety concerns of fluoride.

Bazian’s primary criticisms are misapplied, because Bazian treats the NRC review as if it were trying to determine effectiveness, rather than safety. The types of studies required to establish effectiveness of a medical treatment, such as fluoridation, are simply not ethically possible when studying the toxicology of fluoride. When Bazian criticizes the NRC for failing to use Randomized Controlled Trials (RCTs), which are the gold standard for effectiveness studies, they reveal a misunderstanding of a toxicological review [Bazian p. 8]. RCTs of the harmful effects of fluoride do not exist because it is unethical to purposely expose humans to any medical treatment with the goal of determining the doses that produce harm.

The types of scientific studies available for toxicological assessment are of four main types:

1. studies on tissues or cells outside of living organisms (in vitro studies)
2. animal studies
3. case reports on humans injured or diseased by fluoride
4. epidemiological studies on humans

The epidemiological studies always involve humans harmed by fluoride through occupational, environmental, accidental or sometimes iatrogenic medical exposure. They never involve intentional controlled exposure with the goal of determining the exposure that causes harm. If the NRC panel had restricted themselves to the type of review Bazian group advocates, a review limited to RCT studies, the NRC would literally have had nothing to review, as there has never been an RCT of fluoride in drinking water. Instead of a rigid set of exclusion criteria for choosing studies, the NRC used an exhaustive search process and were open to all forms of relevant evidence. Their final report provides over 500 pages of detailed summaries and conclusions of their findings. They used a weight-of-evidence approach to making decisions. This is the standard approach used in toxicology reviews where, by necessity, most of the scientific evidence is not available in studies that can be compared quantitatively.

The 12 members of the NRC 2006 panel were selected by the US National Academies of Science for their recognized expertise in the fields of toxicology, risk assessment, epidemiology, and experience on fluoride health effects. They spent thousands of hours over three years and reviewed over 1000 scientific papers, most of which had been published since the previous NRC 1993 review of the toxicology of fluoride. They received no compensation for their work. The US EPA commissioned the NRC, a branch of the National Academies, to do the review. The National Academies is the most prestigious independent scientific body in the US, founded to provide scientific advice to US government agencies.

The NRC panel held public meetings to receive additional information and ask questions of experts. The report was carefully peer reviewed by 14 outside experts. None of these peer reviewers suggested the NRC report had missed any relevant evidence. Another primary criticism the Bazian group makes of the NRC report reveals their misunderstanding of exposure assessment in toxicology. The Bazian group frequently claim that scientific studies dealing with animals or humans exposed to drinking water with fluoride concentrations of 2 mg/L or greater are irrelevant to anyone in Southampton where the concentration in drinking water will be 1 mg/L.

There are two misunderstandings. First, toxicologists and medical researchers have long known there is a wide range of sensitivities to any substance amongst different people. A 10-fold, or greater, range of sensitivity within a population is common. This is due to a variety of factors, including genetic differences, environmental co-factors, differences in nutritional status, differences in absorption and metabolism, etc.

Because of this range of sensitivities a “safety factor” is a fundamental principle in toxicology. When extrapolating from epidemiological or animal studies to a large population like Southampton, a safety-factor of 100 is common and a safety-factor of 10 is usually the minimum. So, when scientific evidence shows harm at 2 mg/L or 4 mg/L, it is toxicological nonsense to claim 1 mg/L is so much lower that it could not possibly cause harm to anyone in a large population.

The second Bazian group misunderstanding is the difference between concentration in drinking water and actual dose to a tissue within the body. Water company employees might be able to keep the fluoride level in the pipes at 1 mg/L, but the eventual dose to human tissues is determined by factors totally outside their control. Individual humans vary greatly in the amount of water they consume and how they absorb and excrete fluoride once it enters their body. Within the population of Southampton some people drink 10 times more water than others. Those are people like athletes, laborers, military, people with certain medical conditions, or simply people who choose to drink a lot of liquids. Once the fluoride is ingested, there is a wide range amongst individuals in their capability to excrete the fluoride and the extent to which it is concentrated and stored in the tissues. For example, anyone with reduced kidney function will excrete less fluoride and therefore will build up higher levels within their bones. For Bazian group to assert that studies of 2 mg/L fluoride are irrelevant to Southampton reveals a fundamental lack of understanding of toxicology.

A graph illustrating the NRC 2006 findings for fluoride exposure and health effects is attached. It shows that several important subgroups will receive enough fluoride exposure from 1 mg/L fluoridated drinking water to put them at risk for identified health effects. [See pdf of letter which contains graph on page 4]

To summarize, the Bazian group has mischaracterized the NRC 2006 review. The NRC 2006 review was a landmark report on the toxicology of fluoride. It was more thorough, of higher quality, and as relevant to fluoridation of Southampton as any of the other reviews cited by SHA.


Chris Neurath
Director of Scientific Research
Fluoride Action Network
American Environmental Health Studies Project


Bazian critique, Feb. 11, 2009: http://www.fluoridealert.org/sha.basian.nrc.feb09.pdf

NRC Review, May 2006: http://www.nap.edu/catalog.php?record_id=11571