Thus , regardless of study design , iodine deficiency had a substantial impact on mental development .
Several review s and meta-analyses have examined the effects of iodine on mental development .
None focused on young children , so they were incomplete in summarizing the effects on this important age group .
The current systematic review therefore examined the relationship between iodine and mental development of children 5 years old and under .
Effects of iodine supplementation during pregnancy on child growth and development at school age.
Growth and development of 207 children ( 49 % males ; mean age 5.4 years [ SD 0.2 ] , range 4 to 7.3 years whose mothers received iodine during pregnancy , and children who received iodine first in their 2nd year , were examined in 1996 ; 192 children ( 49 % males ; mean age 6.5 years [ SD 0.2 ] , range 5.8 to 6.9 years ) whose mothers received iodine while pregnant were seen in 1998 . Children were from the southern part of China 's Xinjiang Province which has the lowest levels of iodine in water and soil ever recorded .  Head circumference but not height was improved for those who received iodine during pregnancy ( compared with those receiving iodine at age 2 ) and for those supplemented before the end of the 2nd trimester ( relative to those supplemented during the 3rd trimester ) . Iodine before the 3rd trimester predicted higher psychomotor test scores for children relative to those provided iodine later in pregnancy or at 2 years . Results from the test for cognitive development result ed in trend only differences between those children supplemented during pregnancy versus later . The results address the question of when maternal iodine supplements should begin in public health programs world wide . Findings may be relevant to the treatment of maternal and newborn thyroid deficiency in industrialized countries , particularly for those infants delivered before the end of the second trimester
Thus , regardless of study design , iodine deficiency had a substantial impact on mental development .
Several review s and meta-analyses have examined the effects of iodine on mental development .
None focused on young children , so they were incomplete in summarizing the effects on this important age group .
The current systematic review therefore examined the relationship between iodine and mental development of children 5 years old and under .