Iodine intake in The United States

Since 1971 the population iodine intake in the United States has been monitored by the NHANES I (1971— 1974), NHANES III (1988-1994) and NHANES 2001-2002. 

Sufficient dietary iodine intake is necessary for the normal biosynthesis of the thyroid hormones. Up until 1980, the daily dietary iodine intake in the United States ranged between 170 meg and 700 meg, with regional variations, which exceeds the recommended daily requiremoit of 150 meg ... 

Iodized Salt. Iodized table salt has been used to provide supplemental iodine to the U.S. population since 1924, when producers, in cooperation with the Michigan State Medical Society (24), began a voluntary program of salt iodization in Michigan that ultimately led to the elimination of iodine deficiency in the United States. More than 50% of the table salt sold in the United States is iodized. Potassium iodide in table salt at levels of 0.006% to 0.01% KI is one of two sources of iodine for food-grade salt approved by the U.S. Food and Dmg Administration. The other, cuprous iodide, is not used by U.S. salt producers. Iodine may be added to a food so that the daily intake does not exceed 225 p.g for adults and children over four years of age. Potassium iodide is unstable under conditions of extreme moisture and temperature, particularly in an acid environment. Sodium carbonate or sodium bicarbonate is added to increase alkalinity, and sodium thiosulfate or dextrose is added to stabilize potassium iodide. Without a stabilizer, potassium iodide is oxidized to iodine and lost by volatilization from the product. Potassium iodate, far more stable than potassium iodide, is widely used in other parts of the world, but is not approved for use in the United States. 

It can be seen in Figure 78.6 that the incidence of thyroid cancer (all forms) is at the same level today as in 1971, with about 4.6 (women) and 2.0 (men). The overall thyroid cancer incidence in Sweden is somewhat higher than the incidence reported from the UK (number of cases/100000/year) 1.4 (men) and 3.7 (women), respectively (Office for National Statistics Registrations, UK, 2006) but clearly lower than that reported in the United States 4.3 (men) and 12.5 (women), respectively. In the US, an increase in incidence of about 4.8% was observed from 1992 to 2002 National Cancer Institute. The increase in thyroid cancer incidence has been postulated to be correlated with an increased iodine intake in a population. There is a suggested increase in thyroid cancer of the papillary type about 20 years after the... 

As is discussed elsewhere in this volume, the United States is considered an iodine-replete nation. Although iodine intake may be decreasing, iodine insufficiency is not thought to be a cause of hypothyroidism or goiter in the United States. Therefore, in this chapter we will review... 

The two most recent NHANES surveys showed that for women of childbearing age and pregnant women, the median UI excretion levels were adequate (127 and I4lpg/1, respectively, in 1988-1994 132 and 173 pg/1, respectively, in 2001-2002) (Table 115.3) (Caldwell et al., 2005). Thyroid hormone, requiring adequate iodine intake, is critical for neural development in utero and in early life. Although cretinism due to iodine deficiency is not a problem in the United States, subtle developmental delays could result from mild maternal iodine deficiency. 

An increase in iodine intake is only the first step in the amehoration of iodine deficiency. The increase must be sustained, which has not always been the case. In the United States, iodine supplementation of salt and other foods has never been mandated by the government. Furthermore, the iodine content of most foods is not listed on package labels. The last market basket analysis for US iodine intake was conducted in 1982—1994, and reported in 1996 (Pennington and Schoen 1996). Public awareness of the primary sources of iodine in the US diet and its importance in our daily diet has not been stressed. 

In the United States, iodine intake is mostly achieved through the consumption of dairy products and bread, due to the use of iodine as a sanitizing and feed supplement in the dairy industry and as a dough conditioner in bread. 

As a result of changes in the iodine content of food products in the United States, iodine intake has varied over the years. 

The incidence of goiter in the United States fell sharply following the introduction of iodized table salt Nevertheless, some residual goiter persists, probably not caused by insufficient iodine intakes, but strongly suggesting causes other than iodine deficiency—such as goitrogens (substances that can cause goiter). 

The FNB-NRC recommends that many added sources of iodine in the American food system, such as iodophors in the dairy industry, alginates, coloring dyes, and dough conditioners, be replaced wherever possible by compounds containing less or no iodine. This recommendation was prompted because the iodine consumed by human beings has increased in recent years, and there is evidence that the quantity of iodine presently consumed in the United States is well above the nutritional requirement. Although there is no direct evidence of an increased human iodine toxicity problem because of the increased intake, there is some concern that if this trend continues, the greater iodine concentration may contribute to an increase in thyroid disorders. 

For example, two regular meals on separate days in a Japanese university hospital contained 195 and 1,290 pg iodine, respectively, and in one home the daily iodine ingestion varied from 45 pg to 1,921 pg/day (12). In the United States and elsewhere, kelp is commonly available in health food stores, and may occasionally contribute to high iodine intake. 

The major dietary iodine sources in industrialized countries are dairy and grain products. Other significant contributors are meat, fish, and poultry, and food additives. The amount of iodine from each food will depend on the source, preparation, processing, and volume consumed. As countries become more industrialized, iodine intake tends to increase, but exceptions exist, such as the decline in dietary iodine in the United States during the past decade. The incorporation of iodine into food is driven largely by commercial rather than health interests, and frequently changes with food industry... 

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