Iodine intake in Denmark

A Danish study of iodine intake in elderly men and women was made in 1988 after a number of studies had suggested that the iodine intake in Denmark has been stable and relatively low for the last 30 years (Pedersen et ai, 1995). AH subjects were born in 1920 and were thus 68-years old at the time of the study. Iodine was measured in a spot urine sample collected in the morning. Careful investigation of the intake of supplementary iodine was taken into account, which none of the previous studies had done. The median urine excretion was 42p,g/l, which indicates moderate iodine deficiency (see Table 116.1). Analyses among users and nonusers of daily iodine supplements indicated that the basic level of iodine intake was overestimated if individual iodine supplementation was not taken into account. About half of the population took no supplements. 

In a prospective study performed to evaluate the effect of 4 years of iodine fortification in Denmark, Vejbjerg et al. (2007) found a lower median thyroid volume among 18—65-year-old subjects, independent of age and indicating approximation to the optimal iodine intake in Denmark judged by thyroid volumes. 

Figure 119.3 Geographical variations in urinary iodine excretion in Denmark before iodine fortification of salt. Median urinary iodine excretion among inhabitants of various Danish cities before iodine fortification of salt, and the estimated number of people living in areas with different levels of urinary iodine excretion. Values were compiled from different studies of urinary iodine excretion, or estimated from measurements of groundwater iodine content. Geographical variation in iodine intake in Denmark is mostly determined by differences in groundwater iodine content. Pedersen etal., (1999) Rasmussen etal., (2000).

IODINE INTAKE IN DENMARK - INFLUENCE ON THE PATTERN OF THYROID DISEASE... 

These studies were somewhat hampered by the lack of knowledge on the frequency of individual iodine supplementation in the form of daily intake of iodine containing vitamin/mineral tablets. Such tablets are commonly employed in Denmark and many brands contain 150 Mg iodine. For a correct interpretation of the results it is necessary to know whether a person participating in a survey takes such tablets. Normally the iodine intake in an area is considered sufficient if the median urinary iodine excretion exceeds a certain value. If a substantial proportion of the population is taking regular iodine supplementation, this may lead to a median excretion vjdue well about what is considered a critical level, and still leave the part of the population which is not taking iodine at risk. 

Data from the Danish Investigation of Iodine Intake and Thyroid Diseases based on a FFQ before iodine fortification was introduced in Denmark. Food with a low iodine content was not included, iodine intake from other sources is a little underestimated and iodine from milk, fish and eggs consequently a little overestimated. Rasmussen efa/., (2002). 

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 Denmark, we studied the incidence of overt hypothyroidism before the Danish iodine program in two areas with a small difference in iodine intake caused by different iodine contents of groundwater. The population hv-ing in the area with only mild iodine deficiency had a considerably higher incidence of overt hypothyroidism than the population with moderate iodine deficiency, whereas the lower iodine intake was associated with more hyperthyroidism (Figure 47.5) (Billow Pedersen et aL, 2002). Subtyping of disease revealed that the difference in hypothyroidism was caused by 50% more cases of spontaneous autoimmune hypothyroidism in the area with the highest iodine intake (Carld et ai, 2006). 

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).

In the same group of women, the incidence of hyperthyroidism was 1.3 cases/1000/year and of hypothyroidism 1.0 cases/1000/year. These data can be compared to data from studies from Denmark (Laurberg et ai, 2006), which show that only a small difference in iodine intake is associated with a large difference in incidence of overt hyper- and hypothyroidism. Thus, the incidence rate of hyperthyroidism for women in a region with moderate iodine deficiency (urinary iodine 45 lig/1) was higher than in a region with mild iodine deficiency (urinary iodine 61pg/l) 1.5 cases/1000/year compared to 1.0 cases/1000/year. In... 

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 exoretion in casual urine samples expressed in two ways in 60-65-year-old subjects living in an area with a relatively high intake of iodine (eastern part of Denmark, Copenhagen), before and after iodization. After fortification, the estimated median iodine exoretion seems to be sufficient, while the iodine oonoentration among elderly women appears to be borderline. Unpublished data from the Danish Investigation of Iodine Intake and Thyroid Disease. N, numbers. 

DanThyr Iodine Intake and Thyroid Disorders in Denmark 1161... 

A program of monitoring was mandatory. In addition to regular measurement of the iodine content of iodized salt and checking the market share of iodized salt in Denmark, monitoring should include investigations of iodine intake and the occurrence of thyroid diseases in areas of both mild and moderate ID before and after fortification. 

The intake of iodized salt by this program was estimated to be around 4g/day, and the iodization level was set to 13 ppm. Bread is a staple food in Denmark, and simulation studies performed by the Danish National Food Agency based on Danish food surveys had shown that iodized salt in bread, in combination with iodized table salt, would distribute the iodine nearly as evenly in the population as iodization of all salt used by the food industry. 

Finally, large amounts of data on disease therapy are continuously collected in various Danish national registries. The third part of DanThyr consists of using these data to compare the use of antithyroid drugs, levothyroxine, the number of patients treated with radioiodine, and the number of thyroid operations in areas of Denmark with different iodine intake levels before and after IF of salt. 

We performed a cross sectional study in the commune of Randers, East Jutland. All subjects bom in 1920 were invited to participate, and 423 (63%) participated. A careful history was taken on the intake of vitamin/mineral tablets and other possible sources of supplementary iodine. In 51.5% of the subjects no evidence of extra iodine intake was obtained. These subjects had a median urinary iodine excretion of 36 Mg/g creatinine in a morning spot urine. In Denmark the daily creatinine excretion in urine is in the order of 1 g in this age group. Regular iodine supplementation in the form of daily intake of iodine containing vitamin/mineral tablets was taken by approximately one third of the population while many took various health products of unknown composition. 

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