Answer: Iodized salt
When you consider what might lead to the whole country roads gaining significant IQ gains, most of us would pay attention to things that are inherent in the nature of cerebral: better-funded colleges, literacy programs, for example .
However, one of the most important effects on IQ levels of American citizens was not standardization of schooling, increased college attendance or literacy, but the introduction of iodine-enriched salt. From 1
So how much impact does the introduction of iodized salt have on IQ levels? Areas in the country without natural iodine sources (eg, inland areas where iodine seafood is rarely consumed) saw an average increase of 15 points over the following decade – an increase of a full scale deviation in just ten years. 19659003] The lessons from the experiment from the beginning of the 20th century on iodizing salt are not lost today. Not only do we continue to add iodine to salt in the United States, but Unicef has led initiatives around the world to educate the public on the benefits of iodized salt in landlocked countries, as well as the benefits of micronutrients to children there.
Picture courtesy of Morton Salt.