A new study indicates that Americans gained up to 15 IQ points after the addition of iodine to salt became mandatory.
In an effort to prevent goiter related to iodine deficiency, authorities ruled that iodine be added to U.S. salt products in 1924.
The iodine, in addition to eliminating goiter, appears to have had an unexpected result: smarter Americans.
In a report published in the National Bureau of Economic Research, James Freyer, David Weil and Dimitra Politi examined data from about two million enlistees for World War II born between 1921 and 1927, comparing the intelligence levels of those born just before 1924 and those born just after.
To do this, they looked to standardized IQ tests that each recruit took as a part of the enlistment process.
While the researchers didn’t have access to the test scores themselves, they had another way of gauging intelligence levels: smarter recruits were sent to the Air Forces, while the less intelligent ones were assigned to the Ground Forces.
Next, the economists worked out likely iodine levels in different cities and towns around America using statistics gathered after World War I on the occurrence of goiter.
Matching the recruits with their hometowns showed researchers that the men from low-iodine areas made a huge leap in IQ after the introduction of iodine.
The men born in low-iodine areas after 1924 were much more likely to get into the Air Force and had an average IQ that was 15 points above that of their slightly older comrades.
This averages out to a 3.5 point rise in IQ levels across the nation.
The World Health Organization backed up these results saying:
‘For iodine-deficient communities, between 10 and 15 IQ points may be lost when compared to similar but non-iodine-deficient populations.’
Iodine comes from food sources, and is especially abundant in seafood and foods grown in coastal areas with high levels of iodine in the soil.
Mountainous and inland areas are often very low in the nutrient, meaning food grown there doesn’t have enough iodine.
Today, iodine deficiency is the leading cause of preventable mental retardation in the world. The condition, known as cretinism, was also common in the U.S. until the introduction of iodized salt.
Originally, U.S. authorities wanted to reduce the incidence of goiter, but research since that time has shown that iodine plays an important role in brain development, especially during gestation.
The World Health Organization estimates that two billion people worldwide are at risk of iodine deficiency.
And it’s not just a Third World problem – the WHO reports that only 27 per cent of households in Europe have access to iodized salt.
The researchers say that iodine may also be a cause of the so-called Flynn Effect, the steady rise in IQ that’s been ongoing since the 1930s.
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