A randomized trial in Ethiopia found iodized salt raised children's cognitive scores by only about 4 IQ points (effect size d=0.17), far below a full standard deviation.

Evidence

Pre‐pregnancy iodized salt improved children’s cognitive development in randomized trial in Ethiopia (NCBI PMC)

Categorization

• XREF: connects to: Iodizing salt in 1924 closed a 15-point IQ gap cheaply; 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. — The Cognitive Effects of Micronutrient Deficiency: Evidence from Salt Iodization in the United States; In populations with severe endemic iodine deficiency, mild mental impairment occurs five times as frequently as cretinism, shifting the population IQ curve 10 points to the left. — Timing of Vulnerability of the Brain to Iodine Deficiency in Endemic Cretinism (+15 more)

Related

• Iodine deficiency impairs brain development in children even without obvious physical effects like goiter, and even relatively low fetal deficiency can significantly reduce IQ. (similarity 0.92)
• 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 0.90)
• Adding iodine to salt beginning in 1924 increased IQ in America by as much as 15 points and boosted the U.S. economy. (similarity 0.90)
• 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 0.89)
• 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 0.89)
• 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 0.88)
• We find that for the one quarter of the population most deficient in iodine this intervention raised IQ by approximately one standard deviation. (similarity 0.88)
• 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 0.88)
• 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 0.88)
• Introduction of iodized salt increased IQ by approximately 15 points for those most deficient in iodine. (similarity 0.88)
• Iodine played a substantial role in cognitive improvements across the American population in the 20th century. (similarity 0.87)
• 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. (similarity 0.87)
• Iodine deficiency is the leading global cause of mental retardation (similarity 0.87)
• In populations with severe endemic iodine deficiency, mild mental impairment occurs five times as frequently as cretinism, shifting the population IQ curve 10 points to the left. (similarity 0.87)
• Iodine deficiency results in a global loss of 10-15 IQ points at a population level and is the world’s greatest single cause of preventable brain damage. (similarity 0.87)

Broader Connections

• Adding iodine to salt in 1924 raised average U.S. IQ scores #contradicts (0.80) — Did iodized salt raise the IQ of 50 million Americans by 15 points?
• Adding iodine to salt closed a 15-point IQ gap cheaply #contradicts (0.80) — Harriet A. Washington, A Terrible Thing to Waste, 18
• Iodine deficiency is a major unrecognized cause of lowered intelligence #contradicts (0.70) — Harriet A. Washington, A Terrible Thing to Waste, 21
• Iodine deficiency is the leading global cause of mental retardation #contradicts (0.70) — The Cognitive Effects of Micronutrient Deficiency: Evidence from Salt Iodization in the United States