The "iodized" emblazoned on the vast majority of salt sold in the US might go by largely unnoticed by the populace, 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 working paper published by the National Bureau of Economic Research (NBER) and reported on by Business Insider 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. But 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 aren’t getting access to the iodized stuff.