The effects of iodine on intelligence in children: a meta-analysis of studies conducted in China.
Level 3 - non-randomized controlled study
Systematic review and meta-analysis of observational and pre-post community studies
What was done
A systematic review and meta-analysis searched Chinese and English databases (Chinese Medical Reference Database, Medline, Cochrane library) for studies conducted in China evaluating IQ (via Binet or Raven scales) in children aged under 16 years. Included studies compared children living in naturally iodine-sufficient (IS) areas with those in severely iodine-deficient (ID) areas, or children born before versus after iodine supplementation programs. Effect sizes were pooled using random-effects models and reported as standard deviation IQ points (SIQP, equivalent to 15 IQ points).
What was found
Across 37 studies encompassing 12,291 children, living in IS communities was associated with an increase of 0.83 SIQP (12.45 IQ points) compared with ID areas without supplementation, 0.82 SIQP (12.3 IQ points) compared with inadequate supplementation, and 0.32 SIQP (4.8 IQ points) compared with supplementation during pregnancy and after birth. In 21 entries, maternal iodine supplementation during pregnancy improved child IQ by 0.58 SIQP (8.7 IQ points) versus persistent maternal ID. Children born >3.5 years after program initiation showed increases of 1.15 SIQP (17.25 IQ points) on Binet scales and 0.80 SIQP (12.0 IQ points) on Raven scales.
Why it matters
This review provides quantitative evidence linking severe regional iodine deficiency to marked cognitive impairment in children, highlighting the critical window of maternal supplementation prior to and during pregnancy.
Limits
All included studies were from China and relied on observational, cross-sectional, or historical pre-post designs rather than randomized trials, leaving potential for residual confounding. Confidence intervals, study quality assessments, and between-study heterogeneity metrics were not reported in the abstract.
Cited by
- partial Iodine deficiency in an infant drops IQ by at least 12 points.