Cognitive consequences of iodine deficiency in adolescence: evidence from salt iodization in Denmark*

Benjamin Ly Serena

doi:10.1111/sjoe.12473

Abstract

AbstractOver the past three decades, many countries have introduced iodized salt policies to eradicate iodine deficiency. Iodine deficiency in utero is detrimental to cognitive ability, but little is known about the consequences of iodine deficiencies after birth. This paper examines the impact of iodine deficiency in adolescence on school performance. I exploit the introduction of iodized salt in Denmark during 1998–2001 as a natural experiment. Combining administrative records on high school grades over a 30‐year period with geographic variation in initial iodine deficiency, I find that salt iodization increases the grade point average of students by 6–9 percent of a standard deviation.

Highlights

More than two billion individuals lack essential vitamins and minerals (WHO et al, 2007), and these micronutrient deficiencies are major causes of disease globally
This paper studies the postnatal effects of salt iodization policy on cognitive performance
If the students were randomly assigned to the treatment and control group, we would expect the opposite – that iodine deficiency is associated with lower grades

Summary

Introduction

More than two billion individuals lack essential vitamins and minerals (WHO et al, 2007), and these micronutrient deficiencies are major causes of disease globally. Over the past three decades, the WHO has initiated global efforts to increase food fortification, which has reduced the incidence of micronutrient deficiencies (Allen et al, 2006). The adoption of iodized salt to eradicate iodine deficiency is a leading example of such food fortification. Iodine is a crucial mineral for metabolic functioning and brain development. While iodized salt has been used since the 1920s in the US and Switzerland to prevent goiter, it became a global health policy after the 1980s, as researchers established that iodine deficiency during pregnancy is detrimental to brain development in children. In 1993, the WHO recommended worldwide adoption of iodized salt, and from 1990 to 2007 a large number of countries introduced salt iodization policies, thereby increasing worldwide access to iodized salt from 20 to 70 percent (WHO et al, 2007)

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