How adding iodine to salt resulted in a decade's worth of IQ gains for the US

Hmmm... Given that we're consuming less iodized salt (ScientificAmerican), I wonder if it's going to have a reverse impact (BusinessInsider via Instapundit):

A new NBER working paper from James Feyrer, Dimitra Politi, and David N. Weil finds that the population in iodine-deficient areas saw IQs rise by a full standard deviation, which is 15 points, after iodized salt was introduced. Since one quarter of the population lived in those areas, that corresponds to a 3.5 point increase nationwide. We’ve seen IQs go up by about 3 points every decade, something called the Flynn effect, so iodization of salt may be responsible for a full decade’s worth of increasing IQ in the U.S.