Broadbent et al. Respond

Grandjean and Choi appear to have misunderstood our sentence about selective readings. The selective readings we referred to were the misinterpretations made in the media and online. Considering the large number of Web sites and news stories still claiming that a “Harvard Study” concluded that “water fluoridation lowers children’s IQ,” further public clarification is needed.

The claim of “an average IQ decrement of about seven points” among children with “elevated exposure” is problematic because it does not clarify what level this “elevated exposure” was, or what it was relative to. We note that the average fluoride concentration of the drinking water in the low-fluoride/high-IQ towns included in the meta-analysis by Choi et al.¹ was within the recommended range for community water fluoridation programs in the 18 studies that considered water fluoride (Figure 1).

FIGURE 1—

Water fluoride concentration in studies included in meta-analysis by Choi et al. (2012).

Note. CWF = community water fluoridation; NZ = New Zealand.

Grandjean and Choi stated that their results do not allow them to make any judgement one way or another about possible levels of risk at levels of exposure typical for CWF. If they are unable to make any such evaluation, it follows that their research is not relevant to the context of community water fluoridation.

In the Dunedin Study cohort, the majority of children who took fluoride tablet supplements did so intermittently and for only a short period of time. We have now estimated average total fluoride intake in our cohort up to age five years, including tablets, toothpastes, and dietary sources. We identified no differences in IQ in childhood or adulthood by total fluoride intake, but we did identify significantly fewer dental caries in both childhood and adulthood among those with higher estimated fluoride intake up to age five years.