The other day I ordered some take-out and it came with packets that had “iodized salt” printed on them. My daughter wondered what that meant. I knew iodine had something to do with my thyroid gland, but not much more, so I decided to look into this further.
What is Iodized Salt?
In Canada, as in many parts of the world, iodine is added to table salt by spraying it with potassium iodate. Plain salt does not expire, but iodized salt has a shelf life of about five years because the stability of the iodized salt decreases over time with exposure, especially in the presence of moisture or metal ions. If you are feeling experimental, you could test for iodine in your salt using stuff you might have in your house already.
Why is Iodine Added?
In the 1920s, a doctor named David Murray Cowie (born in New Brunswick) was working in Michigan, where goiter was so common, it was part of something called the "goiter belt". Goiter is a condition usually associated with iodine deficiency and results in a swelling of the thyroid gland. The thyroid gland needs iodine to make hormones used for metabolism throughout your body and is also crucial to brain development in infants. Cowie advocated adding iodine to the salt as an inexpensive and reliable way to increase iodine intake. This was back when people actually cooked their own food and used salt regularly. They first tried iodized salt in Michigan in 1924 and the occurrence of goiter fell from 30% to under 2%. The following year, the rest of the United States adopted this program. Worldwide, about 70% of households have access to iodized salt, but iodine deficiency is still a concern in places.
How Useful Is Iodized Salt?
Nowadays, we tend to have too much salt in our diets, yet we are getting less iodine. Processed foods tend to be high in salt that is not iodized. For most North Americans, iodized salt is probably only a fraction of our iodine intake.
Other Sources of Iodine
We don’t need a lot of iodine (150 micrograms a day for adults, more for pregnant or breast feeding women for the development of their child) and measuring it is not simple. The best strategy seems to be eating a variety of foods. Dairy and meat products used to contain more iodine because it was fed to livestock and used to disinfect the machinery, but this practise is less common these days. Things from the sea, seafood and seaweeds, are good sources of iodine. During the cold war, some people kept iodine pills in case of a nuclear attack. The idea was that taking them would keep your thyroid from accumulating radioactive iodine, as though that would be your biggest problem.
If you eat anywhere near a sensible diet, your iodine intake should probably be okay. But I am not a medical doctor or dietician, so take this advice with a grain of iodized salt.