Effects of Iodized Salt and Iodine Supplements on Prenatal and Postnatal Growth: A Systematic Review.
What this study found
Overall, iodine repletion did not show clear, consistent benefits for prenatal or postnatal somatic growth, and the certainty of evidence was low to very low. A positive birthweight effect was seen only in severely iodine-deficient pregnant women: MD = 200 g; 95% CI: 183, 217 g; n = 635; 2 non-RCTs. Postnatally, iodine improved growth-related biomarkers rather than growth itself, with increases in IGF-1 (MD = 38.48 ng/mL; 95% CI: 6.19, 70.76; n = 498; 2 RCTs) and IGFBP-3 (MD = 0.46 μg/mL; 95% CI: 0.25, 0.66; n = 498; 2 RCTs). The review concludes that more rigorous, adequately powered trials…
- Study & population
- Systematic review of 18 studies (13 randomized trials, 4 non-randomized trials, and 1 controlled before-after study) including 5729 participants.
- Intervention
- The interventions evaluated iodine repletion delivered as iodized salt, iodine tablets, iodized oil injections, iodine-containing prenatal multivitamins, and other iodine-fortified vehicles.
- Key limitation
- Evidence quality was low to very low, and few well-designed trials directly addressed growth outcomes.
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Open PDFOriginal abstract
Hypothyroidism due to iodine deficiency can impair physical development, most visibly in the marked stunting of myxedematous cretinism caused by severe in utero iodine deficiency. Whether iodine repletion improves growth in noncretinous children is uncertain. Therefore, the aim of our systematic review was to assess the effects of iodine fortification or supplementation on prenatal and postnatal growth outcomes in noncretinous children. Following Cochrane methods and PRISMA (Preferred Reporting Items for Systematic Reviews and Meta-Analyses) reporting guidelines, we searched 10 databases including 2 Chinese databases (latest search February 2017). We included randomized and nonrandomized controlled trials (RCTs; non-RCTs), controlled before-after (CBA) studies, and interrupted time-series studies in pregnant women and children (≤18 y), which compared the effects of iodine (any form, dose, regimen) to placebo, noniodized salt, or no intervention on prenatal and postnatal growth outcomes. We calculated mean differences with 95% CIs, performed random-effects meta-analyses, and assessed the quality of evidence with the use of GRADE (Grading of Recommendations Assessment, Development and Evaluation). We included 18 studies (13 RCTs, 4 non-RCTs, 1 CBA) (n = 5729). Iodine supplementation of severely iodine-deficient pregnant women increased mean birthweight [mean difference (MD): 200 g; 95% CI: 183, 217 g; n = 635; 2 non-RCTs] compared to controls, but the quality of this evidence was assessed as very low. Iodine repletion across the other groups showed no effects on primary growth outcomes (quality of evidence mostly low and very low). Meta-analyses showed a positive effect in moderate-to-mildly iodine-deficient schoolchildren on insulin-like growth factor-1 (MD: 38.48 ng/mL; 95% CI: 6.19, 70.76 ng/mL; n = 498; 2 RCTs, low-quality evidence) and insulin-like growth factor binding protein-3 (MD: 0.46 μg/mL; 95% CI: 0.25, 0.66 μg/mL; n = 498; 2 RCTs, low-quality evidence). In conclusion, we identified few well-designed trials examining the effects of iodine repletion on growth. We are uncertain whether prenatal iodine repletion increases infant growth. Postnatal iodine repletion may improve growth factors but has no clear effects on somatic growth. Our systematic review was registered with PROSPERO as CRD42014012940.