Saturday, August 23, 2014

How Salt Made Us Smarter

This is an interesting story, but it takes a little telling.  Let me lay it out in steps.

1.  There is a disease called goiter, the enlargement of the thyroid gland at the base of the neck.  It used to be rather common but has been wiped out almost entirely in developed countries.

2.  French scientists identified iodine, a micronutrient,  in the 19th century in work with seaweed.  Over time, they found that the rate of goiter was much lower in localities where iodine was abundant -- places near the ocean, where saltwater fish was eaten and where fruits and vegetables grew in soil near saltwater.

3.  In 1917, the United States drafted 2.5 million men for the armed services for World War I.  All the draftees were given medical tests to determine their fitness to serve.

4.  After the war, scientists assembled the data from the medical tests.  They found that soldiers from certain areas -- particularly the Upper Midwest and the Pacific Northwest -- were far more likely to have goiter than any other draftees.  In a number of cases, these men were rejected for military service because goiter had so enlarged their necks that they could not close the top buttons on their uniform shirts.

5.  In late 1924, to reduce the incidence of goiter, the Morton Salt Co. began adding iodine to its table salt, calling the product "iodized salt."  The product was touted and discussed nationally, and other salt companies quickly followed suit.

6.  The campaign worked.  The incidence of goiter in the United States dropped precipitously.

7.  In the early 1940s, the United States declared war against Japan and Germany and began drafting men to serve in the armed forces.  Draftees again were examined for fitness to serve.

8.  In addition to medical exams, the World War II draftees were given IQ tests.  (Men with the highest IQ scores went into the Army Air Corps, presumably because of the technical aptitude required to deal with airplanes.  Other draftees went into different service branches.)

9.  At at the end of World War II, the results of the tests on draftees (men born between 1920 and 1927) yielded mountains of data that were analyzed. The intelligence tests revealed an unexpected other beneficial effect of iodized salt -- smarter soldiers.

10.  Researchers isolated IQ test scores from the parts of the country where goiter had been common earlier.  Then they separated the tests of those men into two groups -- the ones born from 1920 to 1924, and the ones born afterward, i.e., after the introduction and broad consumption of iodized salt.

11.  The results were startling.  The average IQ scores of soldiers born after the introduction of iodized salt were a full standard deviation -- 15 IQ points -- higher than the average scores of soldiers born before salt was iodized.

12.  Later studies by the National Bureau of Economic Research concluded that adding iodine to table salt had led to a 3.5 percent increase in the average national IQ.

Iodine Today

We now understand that many more problems than goiter can be traced to iodine deficiency:  mental retardation, fibrocystic breast disease, breast cancer, hypothyroidism, decreased fertility and infant mortality.  (An excess of iodine also can cause serious problems.)

But the iodized salt experiment was so successful that nobody talks much about this micronutrient anymore.   Accordingly, questions are starting to be raised about whether Americans are getting enough iodine.

It has been estimated that 75 to 90 percent of the salt Americans consume comes from packaged and processed foods, which are made with salt that is not iodized.

Where iodine once was used to fortify wheat, bakers now use bromide, which makes for fluffier bread loaves and cakes, and which some  believe may block the activity of iodine.

Some nutritionists believe that the iodine in iodized salt loses potency relatively rapidly, especially in areas with moist climates.

In May of this year, the journal Pediatrics estimated that one-third of pregnant women were iodine-deficient, a particular worry because iodine is critical to the development of children's brains and nervous systems.

On the other side, there are these facts:

     -- Iodine also is found in soy and dairy products, and inland people now have access to and eat more ocean fish and shrimp, which contain iodine.

     -- Many multiple vitamins include iodine.

One thing that interests me is that a lack of iodine may lead to breast cancer and hypothyroidism.  We all know that the rate of breast cancer is up (although that may be due to more aggressive detection efforts), and I seem to know an awful lot of people with hypothyroidism.

Interestingly, the rate of breast cancer is very low among Japanese women, whose diets include lots of iodine-rich seaweed.  Japanese people also consume more salt than we do, and they live longer than Americans.

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