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The Cognitive Effects of Micronutrient Deficiency: Evidence from Salt Iodization in the United States

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  • James Feyrer
  • Dimitra Politi
  • David N. Weil

Abstract

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.

Suggested Citation

  • James Feyrer & Dimitra Politi & David N. Weil, 2013. "The Cognitive Effects of Micronutrient Deficiency: Evidence from Salt Iodization in the United States," NBER Working Papers 19233, National Bureau of Economic Research, Inc.
    • Handle: RePEc:nbr:nberwo:19233
    Note: CH DAE DEV EFG EH
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    More about this item

    JEL classification:

    • I18 - Health, Education, and Welfare - - Health - - - Government Policy; Regulation; Public Health
    • I28 - Health, Education, and Welfare - - Education - - - Government Policy
    • J24 - Labor and Demographic Economics - - Demand and Supply of Labor - - - Human Capital; Skills; Occupational Choice; Labor Productivity
    • N32 - Economic History - - Labor and Consumers, Demography, Education, Health, Welfare, Income, Wealth, Religion, and Philanthropy - - - U.S.; Canada: 1913-

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