A 2013 study found a gradual increase in average intelligence of 1 standard deviation, 15 points in iodine-deficient areas and 3.5 points nationally after the introduction of iodised salt.

Evidence

Iodised salt (Wikipedia)

Categorization

• corroborated: 2 independent passages support this claim
• XREF: connects to: Adding iodine to salt closed a 15-point IQ gap cheaply — Harriet A. Washington, A Terrible Thing to Waste, 18; Results are consistent with iodization raising IQ by 15 points in iodine-deficient areas and a nationwide average increase of ~3.5 IQ points. — The Cognitive Effects of Micronutrient Deficiency: Evidence from Salt Iodization in the United States; We find that for the one quarter of the population most deficient in iodine this intervention raised IQ by approximately one standard deviation. — The Cognitive Effects of Micronutrient Deficiency: Evidence from Salt Iodization in the United States (+22 more)

Related

• Results are consistent with iodization raising IQ by 15 points in iodine-deficient areas and a nationwide average increase of ~3.5 IQ points. (similarity 0.96)
• Introduction of iodized salt increased IQ by approximately 15 points for those most deficient in iodine. (similarity 0.94)
• Salt iodization beginning in 1924 raised IQ by approximately one standard deviation (15 points) for the quarter of the population most deficient in iodine. (similarity 0.94)
• A 2017 study found that the introduction of iodized salt in 1924 raised IQ for the one-quarter of the population most deficient in iodine. (similarity 0.94)
• We find that for the one quarter of the population most deficient in iodine this intervention raised IQ by approximately one standard deviation. (similarity 0.93)
• Adding iodine to salt beginning in 1924 increased IQ in America by as much as 15 points and boosted the U.S. economy. (similarity 0.93)
• Americans gained up to 15 IQ points after iodized salt became mandatory in 1924. (similarity 0.92)
• Salt iodization raised IQ scores of millions of people by 15 IQ points in iodine-deficient regions and is highly cost-effective at pennies per person per year. (similarity 0.92)
• Iodized salt raised IQs by a full standard deviation (15 points) in iodine-deficient areas, and may explain a decade’s worth of the Flynn effect. (similarity 0.92)
• The lower range of estimates is consistent with iodization raising IQ by 15 points, but also documents at least 10,000 excess deaths from iodine-induced hyperthyroidism. (similarity 0.90)
• Men from the lowest-iodine areas born in 1924 or later had an average IQ that was 15 points higher than their predecessors. (similarity 0.89)
• Iodine played a substantial role in cognitive improvements across the American population in the 20th century. (similarity 0.89)
• For the quarter of the population most deficient in iodine, salt iodization raised IQ by approximately one standard deviation, explaining roughly a decade’s worth of the Flynn Effect. (similarity 0.88)
• In low-iodine counties, the probability of assignment to the Air Forces rose significantly after the introduction of iodized salt. (similarity 0.87)
• Morton Salt began nationwide iodized salt distribution in 1924; access to iodine, a key determinant of cognitive ability, rose sharply. (similarity 0.87)