Fluoride Action Network

An Examination of Statements by US Public Health Officials on Fluoride Toxicity: Part 3

FAN Science Watch | Oct. 19, 2004 | By Michael Connett

In this bulletin, we address a statement from another State Dental Director: Dr. Mark Greer, the Director of Hawaii’s Division of Oral Health.

Back in the year 2001, when the State Legislature in Hawaii was considering a bill on water fluoridation, Dr. Mark Greer submitted a letter to the Senate assuring them of the safety and effectiveness of fluoridation. In his letter, Greer stated the following:

“At the concentrations utilized to fluoridate drinking water, fluoride is not toxic. It’s estimated that in order for a 154 pound person to receive a toxic dose of fluoride, that person would need to drink 585 gallons of optimally fluoridated water at one time”.

To begin answering what is wrong with Greer’s claim, let us first demarcate the dose he is referring to.

If a person consumed 585 gallons of fluoridated water at one time, he/she would ingest a total of 2,214 milligrams of fluoride, or 2.2 grams. For a 154 pound adult, this would translate into a dose of ~32 mg of fluoride per kilogram of bodyweight.

Thus, Greer’s statement can be translated as follows: For a human being to receive a “toxic dose” of fluoride, they would need to ingest 32 mg of fluoride for every kg of bodyweight.

This is the Dental Director’s claim. Is it true? Consider the following:

Fact #1:

The dose that Greer chose as the minimum “toxic dose” for humans is, in actual fact, a dose known as the “Certainly Lethal Dose” or the LD100.

An LD100 (Lethal Dose 100%) is the dose that would be anticipated to kill 100% of the organisms exposed to it. In the case of humans, the LD100 for fluoride is estimated to be 32 to 64 mg per kg of bodyweight (Whitford 1987; Hamilton 1992). According to Whitford (1987), “every 70 kg adult who ingests [32 to 64 mg/kg] would be expected to die.”

If Dr. Greer is correct, it means that the minimum dose of fluoride that can inflict a toxic effect on a human, is the same dose of fluoride which will kill up to 100% of the humans exposed to it. Needless to say, this is rather absurd.

Fact #2:

As would be expected, the toxic dose of fluoride is far lower than the dose that kills 100% of the population.

In 1987, Whitford reviewed the literature in an attempt to determine the dose that would induce an immediate toxic effect. Based on his review, Whitford concluded that 5 mg/kg of fluoride is a “dose that could cause toxic signs and symptoms, including death, and that should trigger immediate therapeutic intervention and hospitalization.” 5 mg/kg is well below Greer’s minimum “toxic dose” of 32 mg/kg.

Whitford, meanwhile, warned members of the public health community against regarding doses below 5 mg/kg as harmless. According to Whitford, the fact that 5 mg/kg is a dose which should result in immediate hospitalization “does not mean that doses lower than 5.0 mg F/kg should be regarded as innocuous” (emphasis in original).

It is instructive to note that Whitford’s review was published 14 years before Dr. Greer made his claim to the Hawaii State Senate.

Fact #3:

Whitford’s warning in 1987 that doses below 5 mg/kg not be viewed as “innocuous” was a prescient one.

Since his review was published, several papers have been published which have documented acute toxic effects from fluoride at doses well below 5 mg/kg (Augenstein 1991; Gessner 1994; Akiniwa 1997). In a 1991 review from officials at a Colorado Poison Control Center, it was reported that some children had suffered acute toxic effects after ingesting doses of fluoride below 1 mg/kg (Augenstein 1991). Three years later, a 1994 report in the New England Journal of Medicine reported that, following a water fluoridation accident in Alaska, some residents experienced acute toxic effects (e.g. vomiting, nausea, stomach pain) after ingesting doses of fluoride as low as 0.3 mg/kg (Gessner 1994); a fact that gained additional credence based on a later review of additional fluoride poisoning incidents (Akiniwa 1997).

0.3 mg/kg is 107 times lower than the minimum toxic dose estimated by Dr. Greer.

Again, it is instructive to note that the New England Journal of Medicine report was published 7 years before Dr. Greer informed the Hawaii State Senate that the minimum toxic dose of fluoride is 32 mg/kg. If Dr. Greer had taken this report into account, his estimate of 585 gallons would have been reduced by a factor of 107 to about 5.5 gallons.

Fact #4:

In terms of hard numbers, Dr. Greer’s estimate of acute toxicity was thus off by a factor of 100+.

While that’s pretty poor – particularly for a public official paid to understand and advise the public on this issue – it does not represent the most glaring problem with Dr. Greer’s claim.

Indeed, the most glaring problem with Dr. Greer’s statement is the underlying logic he utilizes to determine the “toxic dose.”

Greer’s logic can be summarized as follows: A “toxic dose” is a dose that will inflict an immediate toxic effect upon an organism. Any dose that doesn’t inflict an immediate effect is thereby “non-toxic.”

The problem with this logic is probably apparent. It is the equivalent of stating that since one cigarette doesn’t kill you, than smoking for life is perfectly safe.

In scientific terms, Dr. Greer has obscured the difference between an “acute” toxic dose and a “chronic” toxic dose. An acute toxic dose is the dose which will produce immediate signs of poisoning. A chronic toxic dose, meanwhile, is the dose which will produce poisoning over an extended course of time.

What makes Dr. Greer’s confusion of these concepts so difficult to comprehend, is that most objections to water fluoridation deal primarily with concerns of chronic toxicity. For example, it is a solidly established fact that fluoride causes an arthritic, disabling bone disease (i.e., skeletal fluorosis). But what is the chronic toxic dose that can cause the early symptoms of this disease, and how does this dose vary based on a person’s genetics, nutritional intake or health status?

Rather than deal with substantive issues such as this, Dr. Greer sidestepped the issue of chronic toxicity completely, and created a straw man argument about acute toxicity.

[See part 1 and part 2 of this series]


Akiniwa, K. (1997). Re-examination of acute toxicity of fluoride. Fluoride 30: 89-104.

Augenstein WL, et al. (1991). Fluoride ingestion in children: a review of 87 cases. Pediatrics 88: 907-12.

Gessner BD, et al. (1994). Acute fluoride poisoning from a public water system. New England Journal of Medicine 330:95-9.

Hamilton, M. (1992). Water fluoridation: a risk assessment perspective. Journal of Environmental Health 54: 27-32.

Whitford GM. (1987). Fluoride in dental products: safety considerations. Journal of Dental Research 66: 1056-60.