The "iodized" emblazoned on the vast majority of salt sold in the US might go by largely unnoticed, but it turns out that it may have had such a profound effect on public health that it raised the national IQ.
Iodine deficiency is the number one cause of preventable mental
retardation, and a new paper published by the National Bureau of
Economic Research (NBER) shows that after iodized salt was
introduced in 1924, the most deficient quarter of the US population
saw its IQs rise by a full 15 points, or one standard deviation.
Averaged over the entire country, that equates to a 3.5 point bump
per person — the equivalent of a whole decade’s worth of IQ growth
according to the Flynn effect, which holds that IQ tends to increase
over time. While salt has virtually extinguished iodine deficiency
in the US, it remains a problem in much of the developing world,
where some 30 percent of citizens do not have access to it.