Intake of iodine

Dasgupta PK, Kirk AB, Dyke JV, Ohira S (2008) Intake of iodine and perchlorate and excretion in human milk. Environ Sci Technol 42 8115-8121... 

A normal rate of thyroid hormone synthesis depends on an adequate dietary intake of iodine. Iodine is naturally present in water and soil, although some soils contain very low amounts. As a result, seafood is a more reliable source of iodine than crop plants. Approximately 1.6 billion people in more than 100 countries live in areas where natural sources of dietary iodine intake are marginal or insufficient. A minimum of 60 j.g of elemental iodine is required each day for thyroid hormone synthesis, and at least 100 j.g/day is required to eliminate thyroid follicular cell hyperplasia and thyroid enlargement (i.e., iodine deficiency goiter). 

An adequate dietary intake of iodine is essential to prevent hypothyroidism. In many areas of the world, dietary iodine intake is insufficient and must be supplemented. There is another element in which a dietary intake may be insufficient that is also associated with thyroid hormone metabolism. This element is... 

Physiologic Function Testing, An example of this application is the assay of thyroid hormone levels in (lie blood winch, in turn, can aid in the assessment of thyroid function. The radioactive iodine uptake test, which involves the administration of a dose of l31l (iodine-131) to the patient, is also a valuable procedure in assessing thyroid function. At present, the technique is best reserved for problem cases rather than used as a primary screening test. The main disadvantage of this test is the effect of the dietary intake of iodine, which reacts in various ways in different individuals. 

There are many forms of hypothyroidism, differing in their cause and age of onset (see Table 31-1). Severe adult hypothyroidism (myxedema) may occur idio-pathically or may be caused by specific factors such as autoimmune lymphocytic destruction (Hashimoto disease). In the child, thyroid function may be congenitally impaired, and cretinism will result if this condition is untreated. Hypothyroidism may result at any age if the dietary intake of iodine is extremely low. Several other forms of hypothyroidism that have a genetic or familial basis also exist.54... 

The release of thyroid hormone following endocytosis of colloid is inhibited by iodide and is known to be reduced with high dietary intake of iodine. This inhibition is due to the inverse relationship between the iodide content of Tg and the digestibility of iodo-Tg by lysosomal peptidase that is, poorly iodinated Tg is more readily digested than richly iodinated Tg. 

RELATION OF IODINE TO THYROID FUNCTION Normal thyroid function requires an adequate intake of iodine without this, thyroid hormone cannot be made, TSH is secreted in excess, and the thyroid becomes hyperplastic and hypertrophic. The enlarged and stimulated thyroid becomes remarkably efficient at extracting the residual traces of iodide from the blood, developing an iodide gradient that may be 10 times normal. In mild-to-moderate iodine deficiency, the thyroid usually succeeds in producing sufficient hormone, in part by preferentially secreting T. In more severe deficiency, as is common in some parts of the world, adult hypothyroidism or cretinism may occur. 

The dietary assessment methods are based on taking a dietary history, such as diet recall (usually 24-h recall, but sometimes for longer periods), diet history (an interview about typical or usual food intake), and food frequency and/or amount questionnaires (food frequency questionnaire, FFQ and/or food amount questionnaire, FAQ, respectively). More details about these methods are discussed by Margetts and Nelson (1997). Intake of iodine from the data obtained is calculated using various national or international food composition databases, such as INFOODS (Scrimshaw, 1997 Schlotke and MoUer, 2000 Braithwaite et al., 2006). There are currently over 150 food composition tables in use around... 

Numerous nutritional factors influence the production of thyroid hormone (Danforth et al., 1979 Azizi, 1978 Burman et al., 1979 Serog et al., 1982) among the most important is dietary intake of iodine (Kopp, 2004). Given the adaptive role that thyroid hormone plays in determining an appropriate life-history strategy, its dependence on dietary iodine for production remains curious. 

Excessive intake of iodine is toxic to animals and may affect humans if the produce of these animals is consumed. 

Iodine is known to be extracted and concentrated in the thyroid gland for the purpose of hormone production. Inhalation intakes of iodine can occur through various mechanisms, leading to potential health risks, especially in the case of radioactive iodine, which when absorbed into the bloodstream may result in significant radiation dose to the respiratory tract and other organs. The major concern is the development of a thyroid carcinoma. 

The intake of iodine during complex treatment in health resorts was determined by measuring iodide excretion in urine over 24h (Figure 36.2). A stay in are iodine spa without special iodine therapy causes only slightly increased iodine excretion. But if applications such as iodine baths,... 

Currently many health resorts offer iodine-containing brine drinking therapies, using iodine waters, for the treatment and prevention of goiters. Here, sometimes relatively large total intake of iodine is still prescribed and followed. Indeed, a goiter caused by iodine deficiency in younger patients can be treated successfully by iodide hence this would actually be a definitive therapy. 

The recommended daily intake of iodine is 150pg for adults, whereas the lowest and maximum intakes per day are 70 pg and 1 mg, respectively, in the Nordic countries. The recommended daily intake of iodine is 90 pg for children 2-5 years, 120 pg for children 6-9 years, and 150 pg for children 10 years and older and adults in Norway (NNR, 2004). Pregnant women are recommended a daily intake of 175 pg, and lactating women 200 pg of iodine. These recommendations are in line with the World Health Organization (WHO, 2001). 

In a substudy of MoBa, including pregnant women grouped as users or nonusers of vitamin and mineral supplements, median urinary iodine excretion per 24 h was 190p,g and 110p,g, respectively (Brantsaeter et al., 2007). In the same study, dietary iodine intake was calculated by a food-frequency questionnaire and a food diary. The dietary intake of iodine among nonsupplement users was below the recommendations, whereas the dietary iodine intake of supplement users was above the recommendations. This demonstrates that supplements may contribute considerably to the total dietary iodine intake. 

Table 37.5 Intake of iodine from different food groups among Non/vegian children ...

The daily protein intake per kg recommended for each age (Table 41.1) was used to calculate the total protein for a representative weight appropriate to the age (Child Growth Foundation, 1996) the derived amount of protein was then used to calculate the daily intake of iodine. The protein and iodine contents, and the specified recommended age range and indications for use of the enteral preparations, were taken from the manufacturers literature. Readers should note that the temporal recommendations for daily iodine intake from birth through childhood, adolescence and into adulthood do not coincide chronologically with recommendations made for amino acid or protein intakes (Tables 41.1 and 41.2). 

Comparison of UI between subjects having regular lunches at the university canteen (9 5 64 pg/g) and a matched (age, gender, history of iodine exposure and intake of iodine tablets) control group of 400 subjects... 

An important point was that daily intake of iodine tablets was reported by 70 subjects ( = 66 females, = 4 males) in the study population. The underlying reasons for iodine medication were a history of goiter ( = 39) and/ or thyroid nodules ( = 31) in 68 participants. The UI was significantly higher in urine samples of these subjects (169 130pg/g), compared to 722 controls without intake of iodine tablets (103 87pg/g, -test, p < 0.05). Of note, iodine tablet intake in only 8% of the study population led to an increase of the mean overall UI from 103 87 pg/g to 109 81 pg iodine/g creatinine (pg/g). 

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. 

In contrast, Rauma et al (1994) found that, although the daily consumption of kelp tablets ensured a sufficient intake of iodine, the use of such supplements may lead to excessive iodine intake. In addition, Key et al (1992) observed that vegans who regularly took kelp supplements had markedly raised concentrations of thyroid-stimulating hormone (TSH) as a result of excessive iodine intake. Thus, it has been suggested that the high iodine content of kelp tablets may cause hyperthyroidism in susceptible individuals. 

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