1971–1974 and 1988–1994 cannot be determined precisely, but they appear to be a function of a food industry response to concerns expressed by FDA that manufacturing practices were causing excessive levels of iodine in the food supply. That is, the reduction may have been due to efforts to reduce iodine in the food supply from a potentially toxic level to a more acceptable level of nutriture for the general population. In the 1970s, chemical analysis of an FDA market basket sample of foods representative of U.S. dietary patterns showed extremely high and increasing levels of iodine in dairy products, grain and cereal products, and meat, fish, and poultry (Park et al., 1981). Sugars and adjunct groups (e.g., pudding mixes, jam, jelly, candies) also contained substantial amounts of iodine. Although the sources of iodine in these foods were not definitely determined, they are likely to have been iodophors used at that time as cleaning agents in dairy production, high levels of iodine added to animal feed, use of red color dyes containing iodine, and iodates used as baking conditioners in the making of breads (Pearce, 2007). FDA shared its concerns about these findings with the food industry (Park et al., 1981). The iodine content of the food supply subsequently dropped.

The current iodine status of the U.S. population is within an adequate range according to generally accepted guidelines for assessing iodine nutriture—although some groups (e.g., pregnant women) may be at higher risk than the general population (Caldwell et al., 2005; Pearce, 2007). Given current levels of iodine intake, what is likely to happen if salt reduction strategies were to be implemented? This is addressed by considering the contribution of iodized salt to total intake of iodine.

Currently, the main use of iodized salt is for home table salt—of which about 70 percent of sales are for iodized salt (Pearce, 2007). Non-iodized salt is used in most food processing and restaurant/foodservice applications (Dasgupta, 2008). Current intake data show that only about 5 percent of sodium comes from the use of table salt (see Chapter 5). Much of the iodine in today’s diets continues to come from non-salt sources (e.g., iodine-containing food additives, processing aids, foods grown in many regions and countries) (IOM, 2005)—sources that would not be affected by salt reduction. Therefore, if 5 percent of sodium in today’s diet is assumed to be associated with iodized salt and the major sodium reduction strategies in this report are addressed to the sodium content of processed and restaurant/foodservice foods, it would appear that the recommended sodium reduction strategies would have minimal impact on iodine intake of the U.S. population. Nonetheless, as a matter of public health prudence, continued and improved monitoring of urinary iodine excretion of the U.S. population and chemical analysis of the iodine content of market basket foods representative of U.S. dietary patterns are warranted.