Diet, iodine sources

Since the fortification of cattle fodder started in 1950, iodine deficiency has been assumed to be eradicated in Norway (Frey, 1986). Although there never has been systematic monitoring of iodine nutrition, several studies in the last decade have shown that the iodine intake in the majority of the population is in the range considered to be sufficient. The majority of studies conducted in Norway have focused on urinary iodine concentrations in selected groups of the population. Calculation of iodine intake based on a food-frequency questionnaires covering the habitual diet in a representative sample of adult Norwegians confirmed that milk and dairy products are a very important iodine source in the diet. The study showed... 

General Aspects of Iodine Sources and Intakes in the Diet, Main Routes of Iodine Metabolism, and Metabolic Roles... 

Iodine is essential in the mammalian diet to produce the thyroid hormone thyroxine deficiency in humans causes goitre. Collectively, deficiencies of iodine, iron, zinc and vitamin A in humans are thought to be at least as widespread and debilitating as calorie deficiencies (Welch and Graham, 1999). The main source of iodine in soils is oceanic salts rather than parent rock, and so deficiency is most widespread in areas remote from the sea (Fuge, 1996). In principle deficiency is easily corrected with dairy supplements. However in practice this is not always feasible. Addition of iodate to irrigation water has successfully corrected widespread iodine deficiency in parts of China where the usual methods of supplementation had failed (Cao et al., 1994 Jiang et al 1997). However there is not much information on the behaviour of iodine in soil and water systems. 

A list of minerals, sources and a summary of some roles are given in Table 15.4. Shortage of some of these minerals in the diet causes well-known and well-defined deficiency diseases such as anaemia, due to lack of iron, and goitre, due to lack of iodine. As with vitamins, partial deficiencies... 

Goiter due to iodide deficiency is best managed by prophylactic administration of iodide. The optimal daily iodide intake is 150-200 meg. Iodized salt and iodate used as preservatives in flour and bread are excellent sources of iodine in the diet. In areas where it is difficult to introduce iodized salt or iodate preservatives, a solution of iodized poppy-seed oil has been administered intramuscularly to provide a long-term source of inorganic iodine. 

Carbohydrates are more plentiful and constant in food supplies throughout the world when compared to other nutrients, such as proteins, vitamin A, folic acid, and iodine. A naturally occurring deficiency specifically in carbohydrates is im-known. However, deliberate omission of carbohydrates from the diet with continued consumption of fat as an energy source can lead to specific problems. Glucose is required as an energy source by the central nervous system. When there is a deficiency of glucose, the body adjusts its metabolism to provide ketone bodies, nutrients derived from fat, which can be utilized by the brain and other parts of the central nervous system. However, excessive production of the ketone bodies can result in acidosis, a lowering of the pH of the blood, which is potentially toxic. 

Iodine is a mineral that is required for the proper function of the thyroid gland. The thyroid gland extracts iodine from nutrients and incorporates it into various hormones. The once-common condition of goiter, an enlargement of the thyroid gland, is an abnormality that results from an effort to compensate for low iodine intake. Goiter can be prevented if iodine is included in the diet. Seafood is one of the best sources of iodine. In areas where seafood is not available, dietary iodine is easily obtained in the form of iodized salt, found in most grocery stores. 

As part of the biogeochemical cycle, the injection of iodine-containing gases into the atmosphere, and their subsequent chemical transformation therein, play a crucial role in environmental and health aspects associated with iodine - most importandy, in determining the quantity of the element available to the mammalian diet. This chapter focuses on these processes and the variety of gas- and aerosol-phase species that constitute the terrestrial iodine cycle, through discussion of the origin and measurement of atmospheric iodine in its various forms ( Sources and Measurements of Atmospheric Iodine ), the principal photo-chemical pathways in the gas phase ( Photolysis and Gas-Phase Iodine Chemistry ), and the role of aerosol uptake and chemistry and new particle production ( Aerosol Chemistry and Particle Formation ). Potential health and environmental issues related to atmospheric iodine are also reviewed ( Health and Environment Impacts ), along with discussion of the consequences of the release of radioactive iodine (1-131) into the air from nuclear reactor accidents and weapons tests that have occurred over the past half-century or so ( Radioactive Iodine Atmospheric Sources and Consequences ). 

Eggs are another source of iodine in the diet, as its content was found to be 45 p,g/100g (Dahl et al., 2004). The fodder for hens is controlled by legislation (Ministry of Agriculture, 2002) and iodine is normally added at 0.5— 0.6mg-l/kg. The iodine content in hen fodder is shown to influence the content of iodine in eggs (Garber et al.,... 

The lysine-free and low-tryptophan powdered drink, XLYS, LOW TRY Maxamaid is suitable for children in the age range 1-8 years. Children aged 1 year with an assumed weight of 10kg, on a 3g amino acid per kg bodyweight diet, and with no other sources of iodine, have an intake of 120 pg/day. Currently, the recommended iodine intake for children is 90 pg/day. An 8-year-old child weighing 25 kg would have iodine intake of 200 pg/day, which is above the recommended level of 120 pg/day. 

Pregnant and lactating women are vulnerable to iodine deficiency if specialized enteral preparations are their sole source of nutrition. Only 9 out of 44 specialized enteral preparations for adults provide the current requirement of 200 pg/day. If the WHO technical consultation presently under review is accepted, then only two preparations will meet the proposed allowance of 250 pg/day. This has particular consequences for the brain development of the fetus and infant if the mother has an iodine deficiency during pregnancy and if she breast-feeds. Generally, standard infant formula are recommended for use by the manufacturers for up to 1 year, but as infants are weaned from approximately 6 months, estimation of iodine intakes can only be approximate as the mixed diet progresses. 

The major natural food source of iodine is fish. The iodine content of fish reflects that of the water they inhabit thus, high levels of iodine are present in marine fish and shellfish compared to freshwater fish (Figure 45.1). Milk and dairy products contain relatively high amounts of iodine and are considered to be the most important sources of iodine in developed countries. The iodine content of milk is largely influenced by the use of iodophors as teat sterilants and equipment sanitizers in dairy husbandry, and the supplementation of animal feeds due to iodine deficiency in dairy cattle, exacerbated by the inclusion of goitrogenic feeds in the diet (COT, 2003). In addition, seasonal variations in the iodine content of foods are particularly evident in cows milk, with greater iodine... 

As the major sources of iodine in the diet are animal based, it is reasonable to suggest that vegans (a strict vegetarian diet of plant foods only) (Table 45.1) are likely to have a low dietary intake of iodine. So where can vegans obtain their dietary iodine ... 

Dietary Supplements As dietary supplements are an important source of iodine in the vegan diet, the accurate assessment of iodine intake from this source is important. The use of dietary supplements by vegans is a crucial factor in determining their iodine intake and assessing whether supplement users could be at risk of excessive intakes of iodine. However, dietary supplements may be a confounding factor in the assessment of iodine intake, as there is uncertainty and variability in their iodine content (Lee et at, 1994). Furthermore, an excessive intake of iodine through some dietary supplements is not difficult because of their concentrated formulation and manufacmrers recommendations about the number of tablets to be taken, which may further exacerbate excessive intake. 

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