I recently learned that all white salt is processed and devoid of some 80 minerals. Is that why iodine is added?
--Name Withheld

Salt, whether of the table salt variety or harvested by vestal virgins under a full moon in October contains almost no iodine, unless it is added.  According to M. G. Venkatesh Mannar, Executive Director The Micronutrient Initiative Ottawa, Canada, and John T. Dunn, Professor of Medicine, University of Virginia Health Sciences Center, Charlottesville, Virginia, U.S.A.¹:

"Since iodine is a constituent of sea water, it is often incorrectly assumed that sea salt contains sufficient iodine for nutritional purposes. The total dissolved salts in seawater contain less than 2 micrograms of iodine per gram of salts, equivalent theoretically to about 3 micrograms of iodine for every gram of recovered sodium chloride (3 parts per million). Even this small quantity of iodine is mostly lost in the residual mother liquor that is drained out during the production process and should be disregarded in calculations to establish the level of iodine supplement."

Mother liquor is the liquid part of a solution that is left over after crystallization.  In other words, when salt is made by evaporation of sea water, the small quantity of iodine that was in the water stays there and does not precipitate out in significant amounts when salt crystals drop out of solution.

The main dietary sources of iodine are seafood, sea vegetation, such as kelp, and until recently dairy products.  With recent changes to sanitary practices at dairy operations, the amount of iodine found in dairy products is decreasing in some parts of the world².  It is also found in foods supplemented with iodine and in vegetables grown in iodine rich locations, typically close to the ocean.

Iodine is added to table salt not to make up for it not being found in salt deposits, but because in some places there is not enough iodine from local dietary sources to prevent the occurrence of goiters, an enlargement of the thyroid gland visible as a swelling of the front of the neck, and cretinism in infants from a deficiency of iodine in the mother's diet during pregnancy.  The Great Lakes, Midwest, and inner mountain areas of the United States were once called the "goiter belt" because a high number of goiter cases occurred there³.  Usually this is caused by iodine-poor soil.

The dietary requirement for iodine is about 150 micrograms (μg) daily for adults, less for children and more for expecting mothers⁴.  Iodine is added to table salt, in the form of potassium iodide (KI) or potassium iodate (KIO3), in most, if not all, developed countries.  In some coutries it may be added to flour also.

As for the rest of the 79 or so minerals, supposedly found in sea salt, the question isn't really what is there, but rather a) can you really taste a difference, and b) are any of those minerals essential for human health and otherwise absent from normal diets.  If you are a frequent reader of KitchenSavvy, you have likely heard me riff on before about claims that you can taste the difference.  If you have a really good sense of taste and a really mild food, then maybe.  For most cooks in most recipes, I would hazard a guess that in a controlled, blind tasting of something like stew, you probably would never know what kind of salt was used.

So, this is the problem I have.  Star chefs spout off recipes calling for sea salt, or flaky kosher salt, or salt harvested from the dark side of the moon.  Readers and viewers happily follow the advice, paying exorbitant prices to buy specialty salts and the salt companies laugh all the way to the bank.  Meanwhile, there is a very real risk to health, due to iodine deficiency, that is completely neglected.  Combine that with a food fad like the 100 Mile Diet and you have a recipe for disaster!

For most foods, plain old boring table salt is all you need.  As a garnish, or maybe in a few special cases, fancy salt may add something, but most of the time, it is just money down the drain.

Oh, and by the way, much of the time the colors in specialty salts are either impurities such as clay that are found in the water where the salt is harvested and have no nutritional value, or coloring agents, such as finely ground charcoal, that are added at the processor to make the salt look exotic.

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