Effects of Iodized Salt and Iodine Supplements on Prenatal and Postnatal Growth: A Systematic Review.

Systematic review of 18 studies (13 randomized trials, 4 non-randomized trials, and 1 controlled before-after study) including 5729 participants. Populations included pregnant women, infants, preschool and school-age children, and adolescents up to 18 years old in settings with severe to mild/moderate iodine deficiency and some iodine-sufficient contexts.

The interventions evaluated iodine repletion delivered as iodized salt, iodine tablets, iodized oil injections, iodine-containing prenatal multivitamins, and other iodine-fortified vehicles. Doses and schedules varied widely across studies, ranging from single intramuscular iodized oil injections to daily 150 to 200 μg iodine tablets during pregnancy and iodine-containing formula or salt-based supplementation in children.

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 are needed to determine whether iodine supplementation truly affects growth outcomes.

Evidence quality was low to very low, and few well-designed trials directly addressed growth outcomes. Studies were heterogeneous in population age, baseline iodine status, intervention vehicle, dose, and outcome timing, which limits comparability. Adverse event reporting was limited, and many analyses were based on small numbers of studies or non-randomized designs.