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


  • James Feyrer
  • Dimitra Politi
  • David N. Weil


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.

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  • 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

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    References listed on IDEAS

    1. Bishai, David & Nalubola, Ritu, 2002. "The History of Food Fortification in the United States: Its Relevance for Current Fortification Efforts in Developing Countries," Economic Development and Cultural Change, University of Chicago Press, vol. 51(1), pages 37-53, October.
    2. Erica Field & Omar Robles & Maximo Torero, 2009. "Iodine Deficiency and Schooling Attainment in Tanzania," American Economic Journal: Applied Economics, American Economic Association, vol. 1(4), pages 140-169, October.
    3. Politi, Dimitra, 2010. "The Impact of Iodine Deficiency Eradication on Schooling: Evidence from the Introduction of Iodized Salt in Switzerland," SIRE Discussion Papers 2010-02, Scottish Institute for Research in Economics (SIRE).
    4. Watson, Tara, 2006. "Public health investments and the infant mortality gap: Evidence from federal sanitation interventions on U.S. Indian reservations," Journal of Public Economics, Elsevier, vol. 90(8-9), pages 1537-1560, September.
    5. repec:aph:ajpbhl:1987:77:2:219-229_3 is not listed on IDEAS
    6. Hoyt Bleakley, 2007. "Disease and Development: Evidence from Hookworm Eradication in the American South," The Quarterly Journal of Economics, Oxford University Press, vol. 122(1), pages 73-117.
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    Cited by:

    1. Douglas Almond & Janet Currie & Valentina Duque, 2017. "Childhood Circumstances and Adult Outcomes: Act II," NBER Working Papers 23017, National Bureau of Economic Research, Inc.
    2. Lazuka, Volha, 2017. "The lasting health and income effects of public health formation in Sweden," Lund Papers in Economic History 153, Lund University, Department of Economic History.
    3. N. Meltem Daysal, 2015. "Early-life medical care and human capital accumulation," IZA World of Labor, Institute for the Study of Labor (IZA), pages 218-218, December.
    4. Leandro De Magalhães & Dongya Koh & Raül Santaeulàlia-Llopis, 2016. "Consumption and Expenditure in Sub-Saharan Africa," Bristol Economics Discussion Papers 16/677, Department of Economics, University of Bristol, UK, revised 07 Oct 2016.
    5. Karen Clay & Ethan Schmick & Werner Troesken, 2017. "The Rise and Fall of Pellagra in the American South," NBER Working Papers 23730, National Bureau of Economic Research, Inc.
    6. Alex-Petersen, Jesper & Lundborg, Petter & Rooth, Dan-Olof, 2017. "Long-Term Effects of Childhood Nutrition: Evidence from a School Lunch Reform," IZA Discussion Papers 11234, Institute for the Study of Labor (IZA).
    7. David B. Audretsch, 2015. "Knowledge spillovers and future jobs," IZA World of Labor, Institute for the Study of Labor (IZA), pages 218-218, December.
    8. Morgan Kelly & Joel Mokyr & Cormac Ó Gráda, 2014. "Precocious Albion: A New Interpretation of the British Industrial Revolution," Annual Review of Economics, Annual Reviews, vol. 6(1), pages 363-389, August.
    9. Victor Lavy & Analia Schlosser & Adi Shany, 2016. "Out of Africa: Human Capital Consequences of In Utero Conditions," NBER Working Papers 21894, National Bureau of Economic Research, Inc.
    10. Gregory T. Niemesh, 2015. "Ironing Out Deficiencies: Evidence from the United States on the Economic Effects of Iron Deficiency," Journal of Human Resources, University of Wisconsin Press, vol. 50(4), pages 910-958.
    11. Leandro Magalhaes & Dongya Koh & Raül Santaeulàlia-Llopis, 2016. "The Costs of Consumption Smoothing: Less Schooling and Less Nutrition," Working Papers 939, Barcelona Graduate School of Economics.

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    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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