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How Our Food Made Us Smarter

July 30, 2013

mortoniodizedsaltAccording to an analysis of more than two million army enlistment records by the National Bureau of Economic Research, the introduction of iodine into the US salt supply did more than just reduce the prevalence of goiter. It also made us smarter.

In 1924 the US government mandated the iodization of salt. At that time, scientists understood that iodine deficiency was a leading cause of goiter, the potentially deadly enlargement of the thyroid gland. By working through Army records of enlistees from across the United States between 1921 and 1924, researchers found that men from low-iodine areas had an average IQ that was 15 points lower than men from high-iodine areas. The results were confirmed by a study conducted by the World Health Organization that found that “For iodine-deficient communities, between 10 and 15 IQ points may be lost when compared to similar but non-iodine-deficient populations.”

The National Bureau of Economic Research’s report may provide an explanation of the Flynn Effect, a generalized and steady increase in the IQ rate in the United States that has taken place since the 1930s. It is now understood that in addition to causing goiter, iodine deficiency also undermines mental and physical development in infants.

While the iodine deficiency has been reduced for most Americans as a result of iodized salt, elsewhere in the world it remains a major public health problem. While the World Health Organization has made a major push to expand the availability of iodized salt around the world, an estimated 30 percent of the world’s population still lacks access.

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