Evidence Level
Strong
Iodine's role in thyroid function is among the most well-established nutrient-organ relationships in medicine. The global iodine supplementation programs (salt iodization) represent one of the most successful public health interventions in history, reducing goiter prevalence by over 70% in many countries. Bath et al. (2013, Lancet) demonstrated that mild iodine deficiency during pregnancy is associated with reduced child IQ scores, supporting the WHO recommendation of 250mcg daily during pregnancy and lactation. For non-deficient populations, additional iodine supplementation offers no benefit and may be harmful.