Iodine and mental development of children 5 years old and under: a systematic review and meta-analysis.
Level 1 - systematic review of randomized trials
Systematic review and meta-analysis containing randomized controlled trials
PubMed 23609774 · doi:10.3390/nu5041384
What was done
A systematic review and meta-analysis of studies indexed in Medline (1980 to November 2011) examined the relationship between iodine and mental development in children 5 years old and under. Studies were categorized into four designs: randomized controlled trials (RCTs) of maternal iodine supplementation, non-randomized trials of maternal/infant supplementation, prospective cohorts stratified by maternal iodine status, and prospective cohorts stratified by newborn iodine status.
What was found
Twenty-three studies were evaluated. Average effect sizes on mental development by study design were: - Maternal supplementation RCTs (2 studies): 0.68 - Maternal/infant non-RCTs (8 studies): 0.46 - Prospective cohorts stratified by maternal iodine status (9 studies): 0.52 - Prospective cohorts stratified by infant iodine status (4 studies): 0.54 The authors report this translates into 6.9 to 10.2 lower IQ points in iodine-deficient children compared with iodine-replete children.
Why it matters
This review aggregates evidence showing that early-life iodine deficiency is consistently associated with substantial mental development and IQ deficits in children under 5 years of age across multiple study designs.
Limits
Only two RCTs met inclusion criteria, with the bulk of evidence derived from observational or non-randomized designs. Noted methodological weaknesses across included studies included omission of major confounders, small sample sizes, lack of cluster adjustment, and absence of separate analyses for verbal versus non-verbal subtests.
Cited by
- partial Iodine deficiency in an infant drops IQ by at least 12 points.