[A preliminary meta-analysis of 36 studies on impairment of intelligence development induced by iodine deficiency]

Since 1980 s', numerous studies on intelligence quotient (IQ) have documented, in the areas prevalent with severe, moderate and even mild iodine deficiency, which is a risk factor for retardation in mental development there. It was purposed for this paper to quantify the relationship between iodine deficiency and mental development in children and to explore the etiological role of iodine deficiency in mental retardation and the protective effects on children's intelligence of iodine supplementation.

A total of 59 independent investigations published during 1980 and 1998 were selected for meta-analysis, including 20 studies on intelligence determined by Raven's Test and 39 by China Benit Scale.

Homogeneity test showed that there was no significant difference in baseline features between two groups (P > 0.05). The hypothesis testing showed that the homogeneity of each study group was obviously statistically significant (P > 0.05). The results demonstrated that IQ in children at risk for iodine deficiency showed a marked drop by 8.94 points with Raven's Test and by 10.80 points with China Binet Scale, respectively, with an average drop of 10 points. Substantial evidence now available has showed that mental retardation can be prevented by effective correction of iodine deficiency through iodine supplement either iodized salt or iodized oil, which is confirmed by an obvious increase in 11.5 points of IQ in average, and in 11.85 by Raven's Test and 11.64 by China Binet Scale, respectively.

Iodine nutrition plays an important and positive role in brain development. Iodine deficiency leads to loss of 10 points of IQ and 11.5 points can be gained for children in the iodine deficiency areas after significant iodine supplement.