We know that Americans depend on iodine-fortified salt, the original "functional food" to deliver this vital nutrient. Since the U.S. pioneered salt iodization in the mid-1920s, iodized salt has been virtually universally available in the U.S. and about 70% of table salt purchases are for iodized salt. Since Americans are eating more and more food prepared outside their homes, prepared both by the full range of restaurants to processed dishes and dinners brought home from the supermarket, however, and many of those foods (including virtually all those produced by food manufacturers) have been processed with plain, not iodized salt, there has been a gradual erosion of iodine in the American diet as "round cans" were less frequently used in home cooking.
A recent article in the authoritative IDD Newsletter by Elizabeth Pearce of Boston University reminded that
The first U.S. National Health and Nutrition Examination Survey (NHANES I), conducted from 1971-1974, reported a median urinary iodine (UI) for the U.S population of 320 μg/L, reflecting adequate to excessive dietary iodine intake. (emphasis added)
She added:
(T)he most recent NHANES survey, conducted from 2001-2002, found that the median UI has stabilized at 168 μg/L
150 μg/L is the recommended intake level, so the U.S. is still slightly over the recommended level, but not by enough to warrant concern about over-consumption. Most people can tolerate at least 1,000 μg/L of iodine daily without adverse effects. People with underlying autoimmune thyroid disease or who have previously been iodine deficient, may tolerate less. Our general concern is with under-consumption, but we must be careful to keep within the "window" of safe intakes.
Faced with much the same situation as the U.S., though more extreme, the decline of iodine intake in New Zealand prompted the government there to mandate use of iodized salt in most breads as a means of slightly increasing the iodine intake of the population. The Salt Institute supported that change. The Salt Institute estimates that in another decade or so some similar adjustment may be necessary in the U.S. The Institute has opened discussions with the food service industry encouraging their use of iodized salt and with food processors to determine if there are technical concerns on the part of food manufacturers to shifting to use of iodized salt. Thus, in the coming years, adding more iodine as required will be as simple as converting one or more products to using iodized salt.
Iodized salt remains the best vehicle to fortify because of the innate salt appetite that has kept per capita salt consumption unchanged in the century-plus that modern instrumentation has been able to measure it.
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