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Dimitra
Politi
Research
papers:
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The Cognitive
Effects of Micronutrient Deficiency: Evidence from Salt
Iodization in the United States (joint with James
Feyrer and David
N. Weil)
Journal of the European
Economic Association, forthcoming
[link
to paper]
[Online
Appendix]
[Replication files]
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 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 upward trend 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.
Selected press coverage:
The
New Yorker, Freakonomics
Blog, Business
Insider
The
effects of the generalized use of iodized salt on
occupational patterns in Switzerland.
[link
to paper]
Abstract
I
estimate the long-term impact of the first large-scale
nutritional supplementation program, salt iodization,
which took place in Switzerland in the 1920s and 1930s.
Iodized salt improved the health environment in utero,
and it eradicated mental retardation caused by
insufficient iodine intake. By exploiting variation in
the pre-existing prevalence of iodine deficiency, as
well as differences in the timing of the intervention
across Swiss cantons, I show that cohorts born in
previously highly deficient areas after the introduction
of iodized salt were more likely to enter top-tier
occupations with higher cognitive demands. As a result,
wages of these cohorts were higher, accounting for about
1.9% of annual median earnings, or 2% of GDP per capita
in 1991.
The
Impact of Iodine Deficiency Eradication on Schooling:
Evidence from the Introduction of Iodized Salt in
Switzerland.
[updated
version coming soon]
Abstract
I
study the impact of salt iodization in Switzerland on
graduation rates. The programme, which began in 1922 and
continues to this day, was the first wide-reaching
nutritional intervention ever to take place. Iodine
deficiency in utero causes mental retardation, and
correcting the deficiency is expected to increase the
productivity of a population by increasing its cognitive
ability. The exogenous increase in cognitive ability
brought about by the iodization program is also useful in
the context of disentangling the effects of innate ability
and education on later-life outcomes. I identify the
impact of iodization on graduation rates by exploiting
pre-existing geographic variation in the prevalence of
iodine deficiency, as well as spatial and temporal
variation in the introduction of iodized salt across Swiss
cantons. By looking at sharp, discontinuous increases in
iodized salt circulation I show that the eradication of
iodine deficiency in previously deficient areas
significantly increased graduation rates from upper
secondary and tertiary education. My results are robust to
falsification tests and different measures of iodine
deficiency.
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Edinburgh School of
Economics