Iodine sufficiency

Thyroid autonomy appears as a solitary toxic nodule or toxic multinodular goitre. In toxic thyroid, the nodule s synthesis and secretion of thyroid hormones is autonomous from the thyroid-stimulating hormone (TSH), which is produced in the pituitary gland. Accordingly TSH is suppressed and the extranodular thyroid tissue is functionally downregulated. Thyroid autonomy occurs frequently in iodine-deficient countries, whereas it is much less common in iodine-sufficient areas. Constitu-tively activating mutations in the TSH receptor and in the Gs a protein are the major molecular aetiology of toxic thyroid nodules. 

Gaitan E, Cooksey RC, Legan J, Cruse JM, Lindsay RH, Hill J (1993) Antithyroid and goitrogenic effects of coal-water extracts from iodine-sufficient goiter areas. Thyroid 3 49-53... 

T4, T3, MIT, and DIT are stored outside the cell in the follicular colloid in peptide linkage within the Tg molecules. In normal humans on an iodine-sufficient diet, Tg makes up approximately 30% of the mass of the thyroid gland and represents a 2- to 3-month supply of hormone. The total amount of iodine contained as T4, T3, MIT, and DIT within Tg varies with the dietary iodine intake. 

A. Soldin OP, Hilakivi-Clarke L, Weiderpass E, Soldin SJ. Trimester-specific reference intervals for thyroxine and triiodothyronine in pregnancy in iodine-sufficient women using isotope dilution tandem mass spectrometry and immunoassays. Clin Chim Acta 2004 349 181-9. 

Hypothyroidism. Hypofunction (insufficiency) of the thyroid gland. Autoimmunity is the most common cause of hypothyroidism in iodine-sufficient countries. See also thyroiditis, autoimmune Hashimoto thyroiditis primary myxoedema. 

Lind P, Langsteger W, Molnar M, Gallowitsch HJ, Mikosch P, Gomez I (1998) Epidemiology of thyroid diseases in iodine sufficiency. Thyroid, 8(12) 1179-1183. 

The association between iodine deficiency and goiter was established long ago (FeUenberg, 1923 McClendon and Hathaway, 1924 Hercus et ai, 1927). The presence of goiter despite iodine sufficiency was also demonstrated early in the 20th century (Lieck, 1927 Scheffer, 1932), but a cause was not unveiled until the 1970s. 

The recommended dietary iodine intakes represent amounts of iodine sufficient to prevent symptoms of deficiency and impairment of health or performance while maintaining the body s store of iodine (see sections Requirements/ Recommendations for Iodine Supplementation and Response Criteria and Dose—Response Studies of Iodine Requirement in Farm Animals ). Recommended daily... 

Iodi2ed salt is the most important source of iodine worldwide, and is also the agreed strategy for achieving iodine sufficiency (WHO/UNICEF/ICCIDD, 2001). Although Norway has never had mandatory iodization of salt, some brands of table salt are fortified with iodine, and regulations permit the addition of 5 pg of iodine per gram of NaCl (Ministry of Health, 2002). Industrial salt used in food production is not supplemented with iodine (Frey, 1986). 

Table 42.1 Daily minimal iodine requirement in normal iodine-sufficient adults...

Women who are iodine-sufficient at conception have natural intrathyroidal iodine reserves that should remain ample (Liberman et ai, 1998), unless iodine intake decreases and the rate of increase in iodine loss exceeds the... 

Pregnancy-related changes in iodine-sufficient women... 

Alcohol consumption is associated with a lower prevalence of goiter and thyroid nodules (Knudsen et ai, 2002). The mechanism behind this association remains unclear. Probably, selenium does not significantly influence thyroid volume in at least borderhne iodine-sufficient populations (Brauer et al, 2006b). Moreover, gender, age and parity can play a role in the pathogenesis of goiter (Knudsen et aly 2002), as discussed later in this article. 

In spite of a mean UI within the range of iodine sufficiency, 36% of the study subjects had mild iodine deficiency with UIs between 50 and 99pg/g. Moreover, 21% of the study population had moderate-to-severe iodine deficiency [UI < 50pg/l (pg/g)]. It should, therefore, be discussed urgently whether it is acceptable to label a population as iodine sufficient according to the WHO criteria eventhough up to 20% of the population can be severely iodine deficient and 36% can be mildly iodine deficient. 

Despite borderline iodine sufficiency in the overall Leipzig population (n = 805), goiter was present in 92 (11.4%) subjects (7% males, 12.5% females). Thyroid nodules were found in 231 (29.6%) subjects ( = 156, single nodule n = 75, >1 nodule), including 68 subjects (6%) with known thyroid disease. 

The validity of the duplicate portion technique may be problematic as the completeness of duplicate portions is often difficult to assess. However, the use of biochemical markers, such as plasma, serum and urine, may be incorporated into nutritional assessment studies to validate dietary surveys or confirm nutritional status. There are a number of different methods that can be used to assess iodine status and, in particular, for the determination of the severity of iodine deficiency. However, two main methods used for the assessment of iodine status are measurement of urinary iodine excretion and thyroid function tests (an indirect method of iodine sufficiency). 

The determination of the levels of thyroxine (T4) and TSH in serum may be used to indicate thyroid function, thus providing an indirect measurement of iodine sufficiency. However, although serum T4 and TSH levels can be accurately and precisely measured, the tests tend to be costly and technically time-consuming. In comparison, measurements of urinary iodine excretion are cheaper and technically simpler, with no requirement to take a blood sample. 

Until the 1990s, total goiter prevalence (TGP) in school-age children was the primary indicator for the assessment of functional consequences of iodine deficiency in the population (WHO et al., 2001). Thyroid size was traditionally determined by palpation, but the reliability of this method is limited by high inter-observer and intra-observer variations. The measurement of thyroid size by ultrasound has therefore been an important step in the detection of mild-to-moderate iodine deficiency. International reference values for normal thyroid size are now available from iodine-sufficient children (Zimmermann et al., 2004). Because TGP is not a sensitive indicator of recent changes in iodine status in the... 

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