The Introduction Of What Led To A Significant Rise In U.S. IQ Levels?
Answer: Iodized Salt
When pondering what could cause entire swathes of the country to enjoy significant IQ gains, most of us would turn our attention to things that are inherently cerebral in nature: better funded grade schools, literacy programs, or college tuition initiatives, for example.
One of the most significant impacts on the IQ levels of U.S. citizens, however, was not standardization of schooling, increased college attendance, or literacy programs, but the introduction of iodine-enriched salt. Starting in 1924, all non-kosher table salt in the US was enriched with iodide, a micronutrient that is incredibly important to neurological development. Not only do children born from mothers who are iodine deficient have lowered cognitive functioning (damage, unfortunately, that cannot be undone later), iodine deficiency is also the leading preventable cause of mental retardation worldwide.
So how big of an impact did the introduction of iodized salt have on IQ levels? Areas of the country with no natural sources of iodide (e.g. inland areas where iodine-rich sea food was rarely consumed) saw an average rise of 15 points over the following decade–a rise of one full deviation on the scale in just ten years.