Iceland iodine intake

Over the years, people living with iodine deficiency tend to develop multifocal thyroid autonomy, and multinodular toxic goiter is a common cause of hyperthyroidism. The difference in relative distribution of the four most common causes of hyperthyroidism in Iceland, with high iodine intake, and Judand, Denmark, with mild-to-moderate iodine deficiency, is shown in Figure 47.3. In Iceland, Graves ... 

Figure 47.3 Nosological types of hyperthyroidism with different iodine intake levels. Relative frequency of the four most common nosological types of hyperthyroidism in Iceland, with relatively high iodine intake from consumption of fish and high iodine content of dairy products, and from East Jutland, Denmark, with mild-to-moderate iodine deficiency. MNTG, multinodular toxic goiter GD, Graves disease STA, solitary toxic thyroid adenoma SAT, subacute thyroiditis. Data from Laurberg et al., (1991).

In a population-based study of 68-year-old people living in Iceland and in Jutland, subclinical hypothyroidism was much more prevalent in Iceland, with sufficient to excessive iodine intake, than in an area of Jutland, with moderate iodine deficiency (Figure 47.4) (Laurberg et al., 1998). Subclinical hyperthyroidism was much more common in Jutland, as discussed above (Figure 47.4). 

Figure 47.4 Serum TSH (mU/l) below and above reference in 68-year-old people from fhe populafion in Iceland and in East Jutland. Prevalence rates of fhyroid hyperfuncfion wifh serum TSH below fhe reference range and fhyroid hypofunction with TSH above the TSH reference range (0.4-4.0mU/l) in 68-year-old people living in Iceland wifh relatively high iodine intake and in Jutland with moderate iodine deficiency. Dafafrom Laurberg etal., (1998).

Figure 60.3 Prevalence rates (%) of Tg-Ab and TPO-Ab in elderly subjects from Jutland, Denmark, with-mild-to-moderate ID, and from Iceland with a stable high iodine intake. Different levels of antibody concentration are shown in each bar. Samples from the two areas were measured in random order in the same assays. Data from Laurberg etal. (1998).

A comparative epidemiological study of thyroid abnormalities in relation to the level of iodine intake was done in Iceland (high-iodine intake, 300pg/day) and Jutland/ Denmark (low iodine intake, 40-70 p,g/day) (Laurberg etal., 1998). 

Notes-. Iodine intake expressed as iodine dietary intake and urinary iodine excretion in elderly males (M) and females (F). The early Danish surveys indicate mild-to-moderate iodine deficiency, even among users of dietary supplements. The 68-year-old Danes were also compared to elderly subjects in Iceland with a long-standing relatively high iodine intake. After the mandatory fortification of salt in 2000-2001, the Danish National Survey 2002 indicates a sufficient iodine intake among elderly subjects. N, numbers 7-D R, 7-days food record FFQ, food frequency questionnaire. 

The pattern in Aalborg is similar to previous findings in another part of Jutland (Laurberg et al., 1999), and the differences between Aalborg and Copenhagen are qualitatively similar to the previously observed differences between Jutland, with a low-iodine intake, and Iceland, with a much higher iodine intake (Laurberg et al., 1998). 

We performed a comparative epidemiological investigation in East-Jutland and in Iceland (5). As mentioned above the iodine intake has been relatively stable at a moderately low level in East-Jutland for many years. On the other hand, the iodine intake has been stable high (300-350 jug/24 h) in Iceland for many years (6). The two areas have a similar level of medical care and socio-economic development and a similar genetic background (7), The person years studied were 569,108 in East-Jutland and 687,342 in Iceland. 

On the other hand a considerably lower incidence of Graves disease among younger subjects as compared to Iceland with a high iodine intake, could warn against increasing the population iodine intake too much. 

In some countries, e.g. Iceland and Japan, intake of fish and/or seaweed is quite high, which is reflected in the iodine excretion (Sigurdsson and Franzson, 1988 Nagataki, 1993. 

---