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 .
The Relation between Neonatal Thyroxine Levels and Neurodevelopmental Outcome at Age 5 and 9 Years in a National Cohort of Very Preterm and/or Very Low Birth Weight Infants
Transient neonatal hypothyroxinemia is very common in preterm infants . The literature on the effect of this hypothyroxinemia is , however , controversial , and large or long-term follow-up studies are not available . In a nationwide prospect i ve follow-up study on very preterm and ( or ) very low birth weight infants ( n = 717 ) , we studied the relationship between thyroxine levels in the 1st wk of life and neurodevelopmental outcome at 5 y of age and school performance at 9 y of age .  Thyroxine concentrations from filter paper eluates were determined in 717 infants : 32 % had levels of more than 3 SD below the mean ( < 60 nmol/L ) . The percentage of infants with such low levels increased with decreasing gestational age . At the age of 5 y , 96 % of survivors(n = 640 ) were available for extensive neurodevelopmental examination : 85 ( 13.3 % ) had a disability and 92 ( 14.3 % ) a h and icap . At the age of 9 y , 83 % of survivors ( n = 552 ) answered a question naire on school performance : 300 ( 54.3 % ) were in mainstream education in a grade appropriate for age , 151 ( 27 % ) were in mainstream education with grade retention , and 101 ( 18.3 % ) were in special education . Both neurologic dysfunction at age 5 y and school failure at age 9 y were significantly related to lower neonatal thyroxine levels even after adjustment for other perinatal factors ( odds ratio , 1.3 ) . Whether this relationship is causal should be investigated . If a causal relationship exists , substitution therapy may at least partially prevent neurologic dysfunction and learning disabilities , both common sequelae of very preterm birth
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 .