Dose for Incipient Acute Fluoride Intoxication: True Science and False Science

Tohru Murakami

Reprinted with permission from Fluoride, 31(1) 1998, pp. 55-56.
Dr. Murakami is Vice President of the Japanese Society for Fluoride Research, 1-5-16 Kamikoide-Machi, Maebashi-Shi, Gunma-Ken, Japan 371

In Japan it is widely believed that the minimum dose of fluoride ion that causes slight or mild, early-stage acute intoxication in humans is 2 mg/kg of body weight. This hypothesis, which may be called the "2-mg theory," was originally proposed by Dr Kinichi Horii, former Professor of Preventive Dentistry at Niigata University School of Dentistry.

At one time Dr. Horii played a major role in advocating fluoridation of drinking water in Niigata Prefecture. Later he promoted a fluoride mouthrinsing program in primary and middle schools after failing to achieve fluoridation of the communal water system in Niigata City, where there was strong public opposition.

His 2-mg theory has been quoted uncritically by many influential health authorities with whom he has close ties. They have not only imposed his program, but they have thereby created the miserable situations by ignoring the symptoms headaches, abdominal pains, nausea and the like of which some children complained after mouthrinsing with fluoride solutions in their schools. But I could hardly ignore what was actually happening, and I spent many years examining the supposed scientific basis of the theory.

For this theory, Dr Horii cited a report by Herbert B Baldwin titled "The Toxic Action of Sodium Fluoride."1 What dumbfounded me when I looked it up was that it was published nearly a century ago in 1899. Such archaic material is not usually found in medical or dental school libraries in Japan. I therefore had to go to the National Diet Library to obtain a copy and was surprised again to learn that it did not provide an acceptable basis for the 2-mg theory. In my report in Japanese,2,3 I gave a detailed discussion of this matter which may be summarized as follows:

"As far as I am able to determine, the 2-mg theory at issue is based on Professor Horii stating: "Baldwin voluntarily tasted sodium fluoride and reported that no effect was produced with 30 mg, slight salivation with 90 mg, and, with 250 mg, nausea after two minutes which became most intense after twenty minutes ... From these facts it is assumed that the amount of fluoride which causes acute intoxication is 2 mg/kg."

I do not think any explanation is needed to recognize that this statement cannot be a scientifically reliable basis for the 2-mg theory. Moreover, Dr Horii has distorted the sense of what Baldwin actually wrote, which was: "Merely tasting small quantities of sodium fluoride produced a slight feeling of nausea with slight salivation. 0.03 gram swallowed with some bread produced no effect. Neither did 0.09 gram taken one hour later, except a little salivation. 0.25 gram, however, taken two days afterward on an empty stomach, produced nausea in two minutes. This gradually increased in severity for twenty minutes when the period of greatest intensity was reached. There was a largely increased flow of saliva and some retching but no vomiting occurred at that time although the desire was very great." It is puzzling how from this passage the conclusion can be reached that "the amount of fluoride which causes acute intoxication is 2 mg/kg."

If we assume Dr Horii took Baldwin's highest sodium fluoride intake figure of 0.25 g (250 mg) as the basis for his calculation, then this quantity of sodium fluoride contains 113 mg of fluoride ion. For a person weighing 56 kg, this amount corresponds to 2 mg F/kg body weight. But at this level of intake the acute toxicity symptoms are already more than slight or early mild.

Dr Horii is considered one of our greatest authorities on fluoride. When he declares fluoride is safe, obedient health officials echo him without question. Nevertheless, if the scientific ground on which he stands is not firm, then his claim for the safety of fluoride is not trustworthy.

In my search of the Japanese literature for information on the acute toxicity of fluoride, I found that the minimum dose reported to cause slight or incipient intoxication ranges from 0.08 to 0.2 mg per kg of body weight, or less than one-tenth of 2 mg/kg.

Dr Kenji Akiniwa has recently extended my work, consulting a very large number of reports, to determine the minimum dose of fluoride that causes slight acute intoxication in humans.4 The result was far below the 2-mg figure proposed by Dr Horii and was very close to what I found above.

As Dr Akiniwa states, fluoride mouthrinsing is a "drug treatment that should be strictly controlled." However, when it is beyond our control, who in fact can control it when it is applied to small children? It is a medical treatment that could be a health risk and should therefore be discontinued.

According to science writers Joel Griffiths and Chris Bryson, recently declassified U.S. government documents shed new light on the beginnings of the still-controversial public health measure, water fluoridation.5 Their research has revealed a surprising connection between public exposure to fluoride and the dawning of the nuclear age in the famous Manhattan Project to build atomic bombs during World War II. Much of the original proof that fluoride is safe for humans in low doses was generated by scientists in that project who had been secretly ordered to provide "evidence useful in litigation" to assist defense contractors facing claims for fluoride injuries caused by their operations in producing atomic weapons.

I just shudder to think how many cases of fluoride poisoning have been covered up by false science.


  1. Baldwin HB. The toxic action of sodium fluoride. Journal of the American Chemical Society 21 (6) 517-525 1899.
  2. Murakami T. Sinwa no hokai suru toki. Shikaitenbo (Dental Outlook) 73 (4) 893-911 1989. [In Japanese, no English title or English summary]
  3. Murakami T. Shiryou (Material). Fluoride Research (Journal of the Japanese Society for Fluoride Research) 10 49-52 1989 [In Japanese, no English title or English summary].
  4. Akiniwa K. Re-examination of acute toxicity of fluoride. Fluoride 30 (2) 89-109 1997.
  5. Griffiths J, Bryson C. Fluoride, teeth and the atomic bomb. Waste Not (82 Judson, Canton, NY 13617, USA) #414 1-8 September 1997 [Abstracted in Fluoride 30 (4) 261-266 1997].