We have all been pretty conditioned these last several years to view food additives of any sort as pure negatives. So it’s interesting to look back to an earlier time and see the effect of an additive that practically no one can argue with. James Feyrer, Dimitra Politi, and David Weil have written a new working paper (abstract; PDF from 2008) about the effect of adding iodine to table salt:
Iodine deficiency is the leading cause of preventable mental retardation in the world today. The condition, which was common in the developed world until the introduction of iodized salt in the 1920s, is connected to low iodine levels in the soil and water. We examine the impact of salt iodization on cognitive outcomes in the U.S. by taking advantage of this natural geographic variation. Salt was iodized over a very short period of time beginning in 1924. We use military data collected during WWI and WWII to compare outcomes of cohorts born before and after iodization, in localities that were naturally poor and rich in iodine. We find that for the one-quarter of the population most deficient in iodine this intervention raised IQ by approximately one standard deviation. Our results can explain roughly one decade’s worth of the upward trend in IQ in the U.S. (the Flynn Effect). We also document a large increase in thyroid related deaths following the countrywide adoption of iodized salt, which affected mostly older individuals in localities with high prevalence of iodine deficiency.
Iodine is hardly the only beneficial additive in our food supply. There’s vitamins A and D in milk. And fluoride in the water? None of these are completely without controversy of course. What other mostly beneficial additives can you think of?
The assault on dietary salt has been growing, and salt sales have been trending slightly downward. Is this a good fight?
According to Scientific American, perhaps not:
This week a meta-analysis of seven studies involving a total of 6,250 subjects in the American Journal of Hypertension found no strong evidence that cutting salt intake reduces the risk for heart attacks, strokes or death in people with normal or high blood pressure. In May European researchers publishing in the Journal of the American Medical Association reported that the less sodium that study subjects excreted in their urine—an excellent measure of prior consumption—the greater their risk was of dying from heart disease. These findings call into question the common wisdom that excess salt is bad for you, but the evidence linking salt to heart disease has always been tenuous.
(HT: Eric Jones)