Iodine appears to have made Americans smarter, the Daily Mail reports.
While the addition of iodine to salt originally was intended to eliminate goiters caused by iodine deficiencies, it appears to have had an unexpected consequence: Americans gained up to 15 IQ points after iodized salt became mandatory in 1924, a new study finds.
The National Bureau of Economic Research recently published a report by economists James Freyer, Dimitra Politi and David Weil that looked at intelligence data from roughly 2 million World War II enlistees born between 1921 and 1927.
The study, which compares the IQ levels of recruits born before 1924 with those born after that year, shows that those who ranked the highest were assigned to the Army Air Forces. Meanwhile, those recruits with lower IQ scores were sent to the Army ground forces.
The economists then researched likely iodine levels in recruits’ hometowns based on the occurrence of goiters in those regions, and they discovered that recruits born in low-iodine areas after 1924 were much more likely to be sent to the Army Air Forces than those recruits born before 1924. In fact, the average IQ of those slightly younger recruits was 15 points higher than that of older recruits.
According to the report, the addition of iodine to salt might be one cause behind the Flynn effect, a long-sustained rise in IQ from roughly 1930 to the present.