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.
Evidence
Timing of Vulnerability of the Brain to Iodine Deficiency in Endemic Cretinism (New England Journal of Medicine)
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 (+11 more)
Related
- 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 0.92)
- 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 0.91)
- 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 0.88)
- Iodine deficiency is the leading global cause of mental retardation (similarity 0.88)
- 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 0.87)
- 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 0.83)
- 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 0.83)
- 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 0.83)
- Iodine played a substantial role in cognitive improvements across the American population in the 20th century. (similarity 0.82)
- 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 0.82)
- Iodine deficiency is a major unrecognized cause of lowered intelligence (similarity 0.82)
- Iodizing salt in 1924 closed a 15-point IQ gap cheaply (similarity 0.82)
- We find that for the one quarter of the population most deficient in iodine this intervention raised IQ by approximately one standard deviation. (similarity 0.81)
- 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 0.81)
- 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 0.80)
Library Connections
- A small average IQ drop hugely swells rates of disability and shrinks giftedness
#expands(0.90) — Harriet A. Washington, A Terrible Thing to Waste, 427
Broader Connections
- Iodine deficiency is a major unrecognized cause of lowered intelligence
#corroborates(0.80) — Harriet A. Washington, A Terrible Thing to Waste, 21 - Iodine deficiency is the leading global cause of mental retardation
#corroborates(0.70) — The Cognitive Effects of Micronutrient Deficiency: Evidence from Salt Iodization in the United States