Relation between excessive iodine intake and mental development of children

  Objective   To describe the relationship of excessive iodine intake with intellectual development of children.

  Methods   Iodine concentrations in drinking water and in urine were assessed in 13 townships in Feng, Pei and Tongshan counties of Jiangsu Province. Based on the median iodine concentration in drinking water, the townships were divided into six groups: water iodine < 100(A), 100-(B), 300-(C), 500-(D), 700-(E) and ≥900μg/L(F). IQ was measured. School children aged 8-15 years with a combined Raven test, weight, height, and urinary iodine concentration data were also collected and compared among 6 groups.

  Results   For children' aged > 11 years, the mean IQ scores of group D(105.5), group E(105.2) and group F(102.3) were significantly lower (P < 0.01) than the mean IQ score of group A(108.9). IQ was related negatively to concentration of iodine in drinking water and in the urine(β=-0.803, β=-0.546 respectively). The IQ of children aged ≤11 years in group F was also lower than their counterparts in group A.

  Conclusion   Excessive iodine intake appeared to impair cognitive development of schoolchildren.

  Results   supported the premise that the maximum allowable iodine concentration in drinking water should be set at 300 or 800μg/L in urine.