Iodine deficiency impairs brain development in children even without obvious physical effects like goiter, and even relatively low fetal deficiency can significantly reduce IQ.

Evidence

Soils and Iodine Deficiency (Springer Nature Link)

Categorization

• corroborated: 2 independent passages support this claim
• 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; 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. — Cretinism - an overview (+12 more)

Related

• 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 0.92)
• 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. (similarity 0.92)
• 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 0.91)
• 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 0.89)
• Iodine deficiency is the leading global cause of mental retardation (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)
• 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 0.88)
• 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 0.88)
• 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)
• 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)
• Iodine played a substantial role in cognitive improvements across the American population in the 20th century. (similarity 0.87)
• Iodine deficiency is a major unrecognized cause of lowered intelligence (similarity 0.87)
• 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 0.87)
• Introduction of iodized salt increased IQ by approximately 15 points for those most deficient in iodine. (similarity 0.86)
• Adding iodine to salt beginning in 1924 increased IQ in America by as much as 15 points and boosted the U.S. economy. (similarity 0.85)

Library Connections

• Iodine deficiency is a major unrecognized cause of lowered intelligence #corroborates (0.90) — Harriet A. Washington, A Terrible Thing to Waste, 21
• Iodine deficiency is the leading global cause of mental retardation #corroborates (0.85) — The Cognitive Effects of Micronutrient Deficiency: Evidence from Salt Iodization in the United States

Broader Connections

• Adding iodine to salt in 1924 raised average U.S. IQ scores #corroborates (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 #corroborates (0.75) — Harriet A. Washington, A Terrible Thing to Waste, 18