When the National Academy of Sciences published the first edition of Drinking Water and Health in the 1970s, the premise was established that adverse effects observed in animals, properly qualified, were indicative of adverse effects that could be expected to occur in humans. This is a big assumption, of course. Humans are not just bigger rats (most of them, anyway).
Consider this study, which examines the effects of differing fluoride concentrations. In the end, data is analyzed by creating statistical categories which to compare to determine if any of the observations are significant using mathematics. However, rats are not statistical categories. They are each unique. Some will see an effect, others will not. Why is this? The “scientist” says we need more data, of course. But I suspect it is not the data that is the primary limitation, but the limitations of statistical methods, virtually by definition. The lack of observed adverse effects does not mean that there are no adverse effects. It just means that none were observed within the methodological and statistical limits of this experiment.
Pereira HA, Leite Ade L, Charone S, Lobo JG, Cestari TM, Peres-Buzalaf C, Buzalaf MA. Proteomic analysis of liver in rats chronically exposed to fluoride. PLoS One. 2013 Sep 17;8(9):e75343. doi: 10.1371/journal.pone.0075343.
Fluoride (F) is a potent anti-cariogenic element, but when ingestion is excessive, systemic toxicity may be observed. This can occur as acute or chronic responses, depending on both the amount of F and the time of exposure. The present study identified the profile of protein expression possibly associated with F-induced chronic hepatotoxicity. Weanling male Wistar rats (three-weeks old) were divided into three groups and treated with drinking water containing 0, 5 or 50 mg/L F for 60 days (n=6/group). At this time point, serum and livers were collected for F analysis, which was done using the ion-sensitive electrode, after hexamethyldisiloxane-facilitated diffusion. Livers were also submitted to histological and proteomic analyses (2D-PAGE followed by LC-MS/MS). Western blotting was done for confirmation of the proteomic data A dose-response was observed in serum F levels. In the livers, F levels were significantly increased in the 50 mg/L F group compared to groups treated with 0 and 5 mg/L F. Liver morphometric analysis did not reveal alterations in the cellular structures and lipid droplets were present in all groups. Proteomic quantitative intensity analysis detected 33, 44, and 29 spots differentially expressed in the comparisons between control vs. 5 mg/L F, control vs. 50 mg/L F, and 5 mg/L vs. 50 mg/L F, respectively. From these, 92 proteins were successfully identified. In addition, 18, 1, and 5 protein spots were shown to be exclusive in control, 5, and 50 mg/L F, respectively. Most of proteins were related to metabolic process and pronounced alterations were seen for the high-F level group. In F-treated rats, changes in the apolipoprotein E (ApoE) and GRP-78 expression may account for the F-induced toxicity in the liver. This can contribute to understanding the molecular mechanisms underlying hepatoxicity induced by F, by indicating key-proteins that should be better addressed in future studies.
Click here for full paper (Open Source).