Background: A recent 2015 study from New Zealand indicated water fluoridation did not have an effect on children’s IQs. A 2012 meta-analysis showed that children with higher fluoride exposure have lower IQs than similar children with lower exposures. Levels of the fluoride ion (F) in blood and urine in children have been linked quantitatively to a significantly lower IQ. The United States Environmental Protection Agency (USEPA) is in the process of developing a health based drinking water standard for fluoride. Objectives: (i) To assess the findings of the recent IQ study on water fluoridation and (ii) to estimate a daily dose of fluoride that might protect children from lowered IQ and be relevant to the pending USEPA standard setting process.
Method: We compared the estimated exposed and control doses received in the recent water fluoridation study, and compared the estimated differences in those exposures to our findings regarding an adverse effect level. We used two methods, both with uncertainty factors, to estimate a protective fluoride dose: the traditional Lowest Observed Adverse Effect Level/No Observed Adverse Effect Level (LOAEL/NOAEL) and the benchmark dose (BMD) methods. We used 3 mg F/L in drinking water as an “adverse effect concentration,” along with the reported fluoride intakes from food, in the LOAEL/NOAEL method. We used the doseresponse relationship in one of the studies cited in the meta-analysis for the BMD analysis. Arsenic, iodine, and lead levels were accounted for in studies we used.
Results and conclusions: Exposure differences between the control and exposed populations in the 2015 water fluoridation study appear to be too small to detect an effect on IQ. BMD analysis shows the possible safe dose to protect against a 5 point IQ loss is about 0.045 mg F/day. The safe dose estimated from the LOAEL/NOAEL method is about 0.047 mg F/day. For 90th percentile children’s body mass at 8–13 yr, these RfDs can be expressed as 0.0010 mg F/kg-day.