Contribution to the ongoing discussion on fluoride toxicity

Abstract

Since the addition of fluoride to drinking water in the 1940s, there have been frequent and sometimes heated discussions regarding its benefits and risks. In a recently published review, we addressed the question if current exposure levels in Europe represent a risk to human health. This review was discussed in an editorial asking why we did not calculate benchmark doses (BMD) of fluoride neurotoxicity for humans. Here, we address the question, why it is problematic to calculate BMDs based on the currently available data. Briefly, the conclusions of the available studies are not homogeneous, reporting negative as well as positive results; moreover, the positive studies lack control of confounding factors such as the influence of well-known neurotoxicants. We also discuss the limitations of several further epidemiological studies that did not meet the inclusion criteria of our review. Finally, it is important to not only focus on epidemiological studies. Rather, risk analysis should consider all available data, including epidemiological, animal, as well as in vitro studies. Despite remaining uncertainties, the totality of evidence does not support the notion that fluoride should be considered a human developmental neurotoxicant at current exposure levels in European countries.

Fig. 1

Correlation of maternal urinary fluoride concentration and full-scale IQ (FSIQ), reproduced from Green et al., . Using this set of data, the authors concluded: “An increase from the 10th to 90th percentile of maternal urinary fluoride was associated with a 3.14 IQ decrement among boys.” (Green et al. 2019). However, because of the relatively high variability of the IQ data, recently calculated benchmark doses of human neurotoxicity (Grandjean 2019) should be treated with caution