Previous | Next | Full Copy

6) Low-Level Fluoride Linked to Sperm Damage in Animals

When given at high doses, fluoride has been found to damage virtually any tissue in the body, whether it be the thyroid, the brain, or the reproductive system. On this, there is now little debate. What is still disputed, however, is whether low levels of fluoride can also cause harm. Towards this end, it will be important for researchers conducting animal studies in the future to put greater focus on low-level effects than has heretofore been the case. In 2007, two research teams did this, in separate investigations of how fluoride ingestion may affect sperm function.

The two studies examined the effect of water fluoride concentrations ranging from 1 to 10 ppm. Since rats and mice are significantly more tolerant to fluoride than humans, 1 to 10 ppm represents a notably low level of fluoride for these animals. It has been estimated, for example, that rats are 5 times less sensitive to fluoride than humans (Turner 1996), and thus a 4.5 ppm concentration would be roughly equivalent to 1 ppm for humans, while 10 ppm fluoride would be roughly equivalent to 2 ppm. It is striking, therefore, that these 2 studies found damaging effects of fluoride on sperm at these levels.

In the study by Reddy, 4.5 ppm (the lowest level tested) was associated with a reduction in sperm count and viability, as well as a reduction in testicular enzyme activity. In the study by Dvorakova-Hortova, 10 ppm was associated with an impairment in “sperm capacitation” - the complex series of events which enable sperm “to obtain full fertilizing capacity.” The authors did not find the same effect from fluoride at 1 ppm. However, when 1 ppm fluoride was combined with aluminum, a similar effect was observed. (It is unclear whether this latter result was an effect of the aluminum itself, or an interactive effect of the aluminum and fluoride.)

As noted by Reddy, “extrapolation of rat data to human beings is always difficult” and, indeed, it is doubtful that the effects observed in these studies would be seen at the same relative levels in humans. Nevertheless, the two studies taken together, do raise added concern about fluoride’s effects on the reproductive system -- especially when considering an earlier study conducted by the then-FDA scientist, Stan Freni, who found a correlation between water fluoride levels exceeding 3 ppm and decreased birth rates in the US. As noted by the NRC (2006) review, “the relationship between fertility and fluoride requires additional study.” These 2 studies add further weight to NRC’s conclusion.

NEXT: 75-85% of U.S. Dentists "Unaware" of Recent Fluoride Research

REFERENCES:

6a) Reddy PS, et al. (2007). Suppression of male reproduction in rats after exposure to sodium fluoride during early stages of development. Naturwissenschaften 94(7):607-11.

6b) Dvorakova-Hortová K, et al. (2007). The influence of fluorides on mouse sperm capacitation. Animal Reproductive Science Aug 6; [Epub ahead of print]

See also: Top 10 Scientific Developments of 2006