Iodization of Salt in 1924 Increased American IQs 15 Points

Iodine deficiency is the leading cause of preventable mental retardation in the world today. The condition, which was common in the developed world until the introduction of iodized salt in the 1920s, is connected to low iodine levels in the soil and water. We examine the impact of salt iodization on cognitive outcomes in the US by taking advantage of this natural geographic variation. Salt was iodized over a very short period of time beginning in 1924. We use military data collected during WWI and WWII to compare outcomes of cohorts born before and after iodization, in localities that were naturally poor and rich in iodine. We find that for the one quarter of the population most deficient in iodine this intervention raised IQ by approximately one standard deviation. Our results can explain roughly one decade's worth of the upwardtrend in IQ in the US (the Flynn Effect). We also document a large increase in thyroid related deaths following the countrywide adoption of iodized salt, which affected mostly older individuals in localities with high prevalence of iodine deficiency.


It dramatically reduced mental retardation, but temporarily increased death by hyperthyroid as iodine-depleted people overdosed.

Folksonomies: public health social welfare

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/health and fitness/disease (0.374398)

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Thyroid (0.968733): dbpedia | freebase | opencyc
Iodine (0.820342): dbpedia | freebase | opencyc
Intelligence quotient (0.788153): dbpedia | freebase | opencyc
Richard Lynn (0.768895): website | dbpedia | freebase | yago
Mental retardation (0.743741): dbpedia | freebase | opencyc
Intelligence (0.716187): dbpedia | freebase
Flynn effect (0.706495): dbpedia | freebase | yago
James R. Flynn (0.636758): dbpedia | freebase | yago

 The Cognitive Effects of Micronutrient Deficiency: Evidence from Salt Iodization in the United States
Periodicals>Journal Article:  Feyrer, Politi, Weil (July 2013), The Cognitive Effects of Micronutrient Deficiency: Evidence from Salt Iodization in the United States, National Bureau of Economic Research, July 2013, Retrieved on 2013-07-24
  • Source Material []
  • Folksonomies: public health public policy social welfare


    11 AUG 2011

     The Science of Social Welfare

    Social Welfare grew from a series of studies that determined children and babies who were malnourished or overly stressed suffered lifetimes of problems behaviorally and economically.