Goal: To study the effects of the fluoride and iodine content of drinking water on child intellectual development and the interaction between the two factors and also the relationship of educational factors to such development.
Methods: The subjects of the investigation were 8- to 14-year-old children randomly selected from endemic areas as well as a control area, with the subjects tested for fluorosis, goiter, and IQ.
Results: In endemic areas with high fluoride and high iodine, there was greater prevalence of both fluorosis and goiter than in the areas with only one of these two factors. Although the high fluoride and high fluoride/high iodine groups showed no significant drop in average IQ compared to the control (p>0.05), in both cases this tendency was present. There was also no significant difference in IQ between the high fluoride and high fluoride/high iodine groups (p>0.05). The IQ scores of the high fluoride/low iodine and low fluoride/low iodine groups each showed significant differences compared to the control (p<0.01). With regard to average IQ, high fluoride and low iodine show significant interaction (p<0.01). In terms of IQ ranking, the high fluoride groups showed significant deficits compared to the control (p<0.01). The average IQ was also significantly linked to the educational level of the parents as well as preschool attendance (p<0.01).
Conclusion: When fluoride and iodine not meeting national standards for drinking water are present in the same area and ingested together, the harmful effects of fluoride are more pronounced, and the resulting damage compounded. However, the damage caused independently by either high or low iodine is greater than that caused by fluoride. Environmental effects related to education also have a direct influence on child intelligence.
Translated by Julian Brooke for the Fluoride Action Network and published with the concurrence of Chinese Primary Health Care 2001;15(3):56-7 in the journal Fluoride.