Iodine in biology
The U.S. Institute of Medicine (IOM) updated Estimated Average Requirements (EARs) and Recommended Dietary Allowances (RDAs) for iodine in 2000. For people age 14 and up, the iodine RDA is 150 μg/day; the RDA for pregnant women is 220 μg/day and the RDA during lactation is 290 μg/day. For children 1–8 years, the RDA is 90 μg/day; for children 8–13 years, 130 μg/day. As a safety consideration, the IOM sets tolerable upper intake levels (ULs) for vitamins and minerals when evidence is sufficient. The UL for iodine for adults is 1,100 μg/day. This UL was assessed by analyzing the effect of supplementation on thyroid-stimulating hormone. Collectively, the EARs, RDAs, AIs and ULs are referred to as Dietary Reference Intakes (DRIs).
Iodine deficiency
With iodine supplementation, goiters caused by iodine deficiency decrease in size in very young children and pregnant women. Generally, however, long-standing goiters caused by iodine deficiency respond with only small amounts of shrinkage after iodine supplementation, and patients are at risk for developing hyperthyroidism. Following the adoption of iodised salt in the United States in 1924, there was a gradual increase in average intelligence of 1 standard deviation, 15 points in iodine-deficient areas, 3.5 points nationally, but also an increase in deaths of older people in iodine-deficient areas due to hyperthyroidism.