Skip to main content
. 2018 Mar 1;10(3):290. doi: 10.3390/nu10030290

Table 2.

Reviews and meta-analyses of the effect of iodine deficiency (ID) on cognitive and neuropsychological development.

Year N of Studies N of Subjects Comments Conclusions
Bleichrodt [32] 1994 21
18		 2676
2214		 Systematic review (21 studies) and meta-analysis (18 studies).
Observational and intervention studies carried out from 1969 to 1991 were pooled		 A number of studies point to a negative effect of ID on cognitive development in children and adults from seriously ID areas, but other studies do not clearly show such an effect.
Meta-analysis: The difference between iodine-deficient and non-ID groups is 13.5 IQ points.
Verhoef [33] 2003 12
15		 --
--		 Meta-analysis
Observational and intervention studies were analysed separately.		 Observational studies indicate that ID is associated with impaired cognitive development.
ID in the first half of pregnancy is irreversible.
Qian [34] 2004 37 12,291 Meta-analysis of Chinese studies
Analysis of observational studies, intervention studies both during and after pregnancy.		 The damage to the intelligence of children exposed to severe ID was profound, demonstrated by a 12.5 IQ point loss; children recovered 8.7 IQ points with iodine supplementation or iodine sufficiency during and after pregnancy.
Melse-Boonstra [35] 2010 7 615 Review of controlled trials (most of them randomized) of iodine supplementation in children. Iodine supplementation in school-aged children can reverse certain delays in cognitive performance.
Iodine supplementation in early life may be more beneficial than supplementation at school age.
Skeaff [36] 2011 8 844 Review of intervention studies carried out in pregnant women in areas of mild-to-moderate ID. There is a need for well-designed trials to determine the effect of iodine supplementation in mildly to moderately iodine-deficient pregnant women on child neurodevelopment.
Trumpff [8] 2013 7
5
5		 3660
425
935		 Three different reviews (all of European studies) of the effect on children’s cognitive/psychomotor development of:
  • -

    maternal hypothyroxinemia.

  • -

    neonatal hyperthyrotropinaemia.

  • -

    odine supplementation.

 It is difficult to establish a direct link between maternal ID and maternal hypothyroxinemia, as well as between maternal ID and elevated neonatal TSH levels at birth.
Some studies suggest that iodine supplementation from the first trimester until the end of pregnancy may decrease the risk of cognitive and psychomotor developmental delay in the offspring.
Bougma [37] 2013 2
8
9
4		 147
1943
2027
2441		 Systematic review and meta-analysis.
Four different analyses:

  1. RCTs with iodine supplementation of mothers (2 studies)

  2. Non-RCTs with iodine supplementation of mothers and/or infants (8 studies)

  3. Prospective cohort study stratified by pregnant women’s iodine status (9 studies)

  4. Prospective cohort study stratified by newborn iodine status (4 studies)

 Iodine deficiency has a substantial impact of mental development.
Average effect sizes were 6.9 to 10.2 IQ points lower in ID children than in iodine replete children.
Quantifying more precisely the contribution of ID to delayed mental development in young children requires more well-designed RCTs, including trials on the role of iodized salt.
Zhou [38] 2013 2
6		 19,683
719		 Systematic review.
2 RCTs conducted in severe ID areas and 6 RCTs in mild-to-moderate ID regions. 		Iodine supplementation during pregnancy or the peri-conceptional period in regions of severe ID reduced the risk of cretinism, but there were no improvements in childhood intelligence, gross development, growth or pregnancy outcomes, although there was an improvement in some motor functions.
Taylor [39] 2014 17 641 Systematic review and meta-analysis.
9 RCTs and 8 observational studies of iodine supplementation during pregnancy from mild-to-moderate ID regions.		 Iodine supplementation improves some maternal thyroid indices and may benefit aspects of cognitive function in school-age children, even in marginally ID areas.
Lam [40] 2017 2 494 Systematic review.
RCTs that evaluate the effect of iodine on cognitive performance or academic performance among children aged 4–18 were included.		 Iodine supplementation achieved a significant improvement in non-verbal fluid intelligence in ID children but no significant change in memory.
Taylor [41] 2017 3 507 Systematic review and Meta-analysis.
RCTs of iodine intervention during pregnancy.		 There was no significant difference between the intervention and control groups for child cognition in any of the RCTs.