The report by Mitchell et al., "No association between fluoridation of water supplies and sudden infant death syndrome"⁴ purported to exonerate fluoride as a possible contributor to sudden infant death syndrome (SIDS). The authors stated: "Analysis was carried out to find the correlation between variables and then simple linear regression was used." The arbitrary selection of linear regression provided a straight line which is very different from the curve of a paradoxical effect, and led to the erroneous conclusion which their title reflects.

The typical paradoxical effect curve that I have inserted in their figure, reproduced below, shows the increase in deaths when fluoride concentration is in the very low range. Professor A W Burgstahler, of the University of Kansas Department of Chemistry, kindly provided the paradoxical effect curve. This was derived by a computer generated least squares best line fit

With paradoxical effects, there can be a critical dose below which one observes an increased adverse effect. The Mitchell et al data suggest such a situation. Within a low concentration range, there are more infant deaths at the low doses than at the higher doses - an inverse relationship. At concentrations above the low concentration range, dose-responses show the direct, linear relationship with which we are familiar: increasing doses are increasingly toxic until a particular dose kills most or all of the test subjects. So there are two different dose-responses to fluoride - a paradoxical effect at very low levels and a linear relationship at higher levels. These two dose-responses are not mutually exclusive; one does not preclude the other.

Most research which purports to demonstrate the safety of fluoridation has not been concerned with very low concentrations of fluoride, at which paradoxical effects occur, for three reasons.
1) individuals vary significantly in fluoride uptake;
2) there is considerable individual variation;
3) it has been unjustifiably assumed that there is a threshold level, namely, the sacrosanct one part per million in drinking water, below which fluoridation is claimed to be safe. The occurrence of paradoxical effects at very low levels of fluoride means that there is no threshold level below which low-level fluoridation is safe.

It is paradoxical that statistics, employed to assure the validity of conclusions drawn from data, can be responsible for concealing paradoxical effects. The fact that statistical analysis of experimental data does not reveal paradoxical effects does not mean that such phenomena do not exist. On the contrary, statistical methods of analysis can effectively prevent recognition of paradoxical effects if the methods do not consider these phenomena. With scattered points, statistical methods are too frequently used to determine where a straight line should be drawn. Too often, the statistical approach assumes that straight lines are the correct lines. Deviations or irregularities caused by paradoxical effects have too often been attributed to experimental variation or errors.

There are additional reasons why the conclusions of Mitchell et al are questionable. The variables they considered were SIDS, mean daily temperature and median fluoridation. They did not consider other important variables, especially the significant intake of fluoride from sources other than fluoridated water, and from baby formulas prepared with fluoridated water. In an earlier study,⁵ Mitchell and others found a significant correlation between SIDS and non-breast feeding. In this later study,⁴ a correlation between mean daily temperature and SIDS was reported. People generally drink more liquids in warmer weather. In neither study did they estimate each infant’s total daily fluoride intake.

Another variable they overlooked is general nutrition, especially calcium intake. The consumption of milk, which is the major source of calcium for infants, is especially important. Our research on fluoridation in Chile (like many other studies) showed that malnourished infants comprise the human population that is most susceptible to fluoride toxicity. It is also well known that calcium protects against fluoride. When Salvador Allende MD became president of Chile in 1970, he initiated a government program under which free milk was delivered daily to pregnant mothers, nursing mothers and every child under the age of 15. At that time, half the children in Chile under 15 years were undernourished, and 600,000 were mentally retarded thorough lack of protein, especially during the first months of life. That was the health status of half the children who were being fluoridated in Chile. I am not implying that malnutrition and/or calcium deficiency were significant factors in SIDS researched by Mitchell et al. No one knows because Mitchell et al did not provide that and other information. To properly evaluate the role of fluoride in SIDS, it is necessary to consider nutrition, especially calcium intake, and total fluoride intake.

Albert Schatz
Professor Emeritus
6907 Sherman Street
Philadelphia
Pennsylvania 19119
USA

REFERENCES

1. Colborn T, Dumanoski D, Myers JP. Our Stolen Future: Are we threatening our fertility, intelligence, and survival? A scientific detective story. Little Brown, London 1996.
   
2. Foulkes RG. The fluoride connection. Fluoride 29 (4) 230-236 1996.
   
3. Schatz A, Schalscha EB, Schatz V. The occurrence and importance of paradoxical concentration effects in biological systems. Compost Science 5 22-30 1964.
   
4. Mitchell EA, Thompson JMD, Borman B. No association between fluoridation of water supplies and sudden infant death syndrome. New Zealand Medical Journal 104 500-501 1991.
   
5. Mitchell EA, Becroft DMO, Barry DM. Results from the first year of the New Zealand cot death study. New Zealand Medical Journal 104 71-76 1991.