Salt iodization iodine supplementation

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. 

Deficiency of iodine, a component of thyroid hormones, may result in goiter formation (see Chap. 73). However, not everyone with an iodine-deficient diet will develop a goiter. Thyroxine (T4) and triiodothyronine (T3) can be used to assess iodine status (see Table 135-8). Intravenous iodine supplements typically are not necessary except during long-term parenteral nutrition with minimal enteral intake. Iodine needs generally are met by cutaneous absorption of iodine from germicides (e.g., povidone-iodine) used in catheter care or consumption of iodized salt. " Use of povidone-iodine wiU likely decrease with the increased use of chlorhexidine for catheter care, and the need for iodine supplementation must be individualized. Iodine excess is rarely a clinical concern when thyroid function is normal. 

The daily requirement for iodine in adults is 1-2 /ag/kg body weight. In the U.S., recommended daily allowances for iodine range from 40 to 120 /xg for children, 150 fxg for adults, 220 fxg for pregnancy, and 270 p,g for lactation. Dairy products and fish have relatively high iodine contents. Because of concerns of iodine insufficiency, iodine supplementation has been widely used for prophylaxis and therapy. The most practical form of this supplementation has been addition of iodide or iodate (now preferred) to table salt. In the U.S., such supplementation is optional and iodized salt provides 100 fxg of iodine/g. 

In 1985, to combat iodine deficiency in the former state of East Germany, salt for human consumption was iodized and iodine was added to animal feed (Anke et al., 1993). Eliminating iodine deficiency in farm animals improved the iodine content of milk and eggs. This further increased the dietary iodine intake of East Germans (see section The Effect of Iodine Intake on the Iodine Gontent of Eggs, Meat and Milk ). The program successfully reduced iodine deficiency in both humans and farm animals, and could be used as a model for iodine supplementation in other countries. 

Acute iodine supplementation is by oral potassium iodide or iodized oil. Long-term iodization is optimally achieved by iodized salt. 

In countries with well-established universal salt iodization (USI) programs and iodine sufficiency, pregnancies probably are not at risk of iodine deficiency. In countries without USI programs and mild ID (most European countries), supplementation can be achieved with 100—200p,g of iodine per day given during pregnancy. 

The most serious and common complication of salt iodization is the development of iodine-induced hyperthyroidism (IIH), which affects mainly older people with nodular goiter another possibifity is the aggravation or even the induction of autoimmune thyroiditis. IIH has been reported in almost all iodine supplementation programs in countries with history of severe ID (Stanbury et ai, 1998). However, IIH can occur following iodine supplementation in areas with previous sufficient iodine intake Galofre et al. (1994) the authors have reported increased incidence of both nodular and Graves hyperthyroidism. Also, increased iodine intake is associated with increased incidence of thyroid autoimmune diseases (Papanastasiou et al, 2000 Zois etai, 2003) (Figure 73.4). 

The mean daily intake of salt in Sweden in 2006 was 12 g, corresponding to 60 pg iodine. It has been estimated that about 75% of Swedish households use iodine-supplemented salt, whereas the use of iodized salt in ready-made food is limited and rapidly diminishing, because of European Union restrictions. High intake of sodium chloride and its association with hypertension has been recognized by the National Food Administration of Sweden, and a long-term program to reduce the total daily intake to 5 g of salt has now been launched. 

Once it is estabhshed that iodine supplementation is necessary, the decision about the best way to provide it is important. There are different ways to provide iodine supplementation through food, viz., salt, oil and water. The efficiency of iodization programs using different vehicles and their impact on the prevention and control of iodine deficiency disorders (IDD) in different countries have been discussed. 

Active prophylaxis (AP) is the provision of iodine supplements to an iodine-deficient population. Beside the individual supplementation of oral iodine and injections of iodized oil, the most common supplementation strategy is the iodization of salt, water and animal feed. Some countries allow only iodized salt to be sold, while other countries allow both iodized and uniodized salt. 

Iodine intake is variable between and within individual countries for several reasons. Many geographic regions have iodine-poor soil resulting in iodine-poor crops and livestock, and eventually in low dietary iodine intake. The proximity to sources of seafood can also affect iodine intake. Region-specific diets, accessibifity to iodine supplements, the availabihty of iodized salt and the extent of its use in food industries, all affect a population s iodine intake. 

Teng et al. (2006) explored the effect of iodine intake on thyroid diseases in China. Baseline characteristics of three populations were estabfished in three communities in 1999 and then again 5 years later. The communities had different levels of iodine nutrition mild deficiency more than adequate and excessive intake. Salt iodization had been implemented in China in 1996. In the general population, median UI increased from 165 pg/1 in 1995 to approximately 300 pg/1 in 1999. The concern was with oversupplementation of iodine to a level that is more than adequate, in a region in which iodine intake was previously mildly deficient, which in turn may accelerate the development of subclinical hypothyroidism to overt hypothyroidism. High levels of iodine intake may increase the incidence and prevalence of autoimmune thyroiditis, making it imperative to tailor supplementation needs to each region. 

The ICCIDD, The United Nations Children s Fund (UNICEF) and the WHO are dedicated to eliminating iodine deficiency, monitoring iodine levels and sustaining optimal iodine nutrition (Atland and Brush, 1952 Markel, 1987 UNICEF, 1998 ICCIDD, 2006). In the last decade there has been substantial progress toward the elimination of iodine deficiency, reflecting the validity of the strategy based on salt iodization and iodine supplementation (WHO, 1999). 

Data from filled questionnaires in the above study showed that iodized salt had been used in the families of all inspected children (100%) over the last 10 years. Elevated median urinary iodine in children living in both areas is most likely due to high levels of iodine added to salt. Hyperthyroidism was reported from other authors in the last years as a side-effect of excessive salt iodization (Delange etal., 2002 Isidro San Juan et al., 2004 Volzke et al., 2003 Zois et al., 2003 Markou et al., 2003). Their findings confirm the necessity for the correction of iodine supplementation. 

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