I have always wondered why our salt was iodized. So the introduction of iodine into salt was due the fact that Iodine deficiency is one of the leading causes of preventable mental handicap. In the US we started requiring salt to be Iodized in 1924. A recent study looked at the long term effects this has had in countries where the change has occurred. The Flynn effect is said to improve IQ by about 3 points per decade.