How salt increased Americans’ IQs

Most American households have a salt and pepper shaker sitting on their kitchen tables. These unassuming flavor additives may seem like a humble way to improve a meal, but salt is a diamond in the rough. The mineral has become a vessel for iodine, delivering numerous benefits to salt consumers. In fact, iodine helps wards off goiter and may even be related to improvements in IQ. Let's take a trip through U.S. history to see how iodine and salt together improved intelligence.

Fighting disease
Goiter is an enlargement of the thyroid that could lead to several complications, including hyperthyroid or hypothyroid, difficulty swallowing or hoarseness. Scientists have known for many years that iodine deficiency is one of the leading causes of this condition. In fact, goiter was so problematic that the U.S. government decided to do something about it. Armed with the knowledge that iodine deficiency can cause goiter, the government mandated in 1924 that all salt manufactured in the U.S. must contain iodine. As such, American dinner tables now all carry iodized salt. 

Goiter occurrences certainly decreased, but the culinary measure brought about significant other results. A study conducted by a group of economists examined data from before and after the introduction of iodized salt, and has concluded that the measure created the unanticipated correlated side effect of increased IQ.

Eating your way to intelligence
The study, published by the National Bureau of Economic Research, looked at enlisted U.S. soldiers around World War II who were born between 1921 and 1927. They then compared data on these men to soldiers born after 1927. The data included results from a standardized IQ exam soldiers must take to determine where they'll be placed. Though researchers weren't given access to the actual scores, they did know that more intelligent people were sent to the Air Force while less intelligent people were placed in Ground Forces.

Researchers then gathered data on which U.S. cities had the largest occurrence of goiter (or iodine deficiency) and cross referenced those towns with military enlistees. They discovered that those who lived in towns with high instances of goiter benefited the most from the introduction of iodized salt, as their IQ leapt. On average, U.S. IQ has increased about 3.5 points since the introduction of iodized salt.

Intelligence now
These results are interesting, especially given what experts already know about iodine and intelligence. Other studies have noted that when pregnant women have an iodine deficiency, their unborn children develop lower IQs. Furthermore, the increase in American intelligence seems to line up with the Flynn Effect, which basically states that humans are getting smarter over time. Is it because of iodized salt, or is that just a small blip? Right now, we don't have the research to answer that question. 

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