Iodine status in the Nordic countries – past and present

Figures & data

Table 1 Comparisons of the Nordic countries regarding geological conditions, iodine levels in water, and historical data on iodine intake levels

	Iceland	Norway	Denmark	Sweden	Finland
Covered by ice during Ice Age	Yes	Yes	Yes	Yes	Yes
Marine sediments	No	No	Yes	South Eastern parts	Southern parts
Water iodine level (median)	0.12 µg/L	<2 µg/L	12.2±8.3 µg/L (mean)	3.7 µg/L	Dug wells: 2.12 (range <0.2–761) mean 10.7±26.8 µg (L Drilled wells 3.04 (range <0.2–232) mean 6.78±35.1 µg(L
Iodine status before iodination	Sufficient	Severe to moderately deficient	Moderate to mildly deficient	Severely deficient	Moderately deficient
Degree of sea fish intake during 1900–1950	High	High in the coastline low in the inland	High in the coastline low in the inland	High in the coastline low in the inland	High in the coastline low in the inland
Fortification of cow fodder historically (starting point)	Fish meal used in cow fodder voluntary	Mandatory from 1950, level: 2 µg/g salt.	Voluntary	Voluntary	Voluntary
Start of iodination to the population		Late 1930s	2000	1936	1946
Type of iodination		Table salt for household use only	Household salt and salt for commercial bread production	Table salt	Household salt and cow fodder
Level of iodine added		5 µg/g salt	13 µg/g salt	50 µg/g salt	25 µg/g salt
Type of legislation		Voluntary	Mandatory	Voluntary	Voluntary
Monitoring by authorities	No	No	Yes	No	Some
Actual cow milk iodine concentration (µg/L)	2006: 85–283 (average 145)	Before year 2000: 150 2000–2012: 100–150 2012–2015: 190 2015: 200		2001: 160 2009: 117	2015: 150
Mean amount of fish by adults (gram per day per person)	National dietary survey in 2010–2011: fish and seafood 46	National dietary survey in 2011: fish and seafood: 67 fish: 52	National dietary survey 2011–2013: 37	National diet survey 2010–2011 fish and shellfish, women 37, men 43	National diet survey 2012 40
Major source for iodine in the population	Fish	Milk	Milk and salt	Salt	Milk
Iodine sufficiency in the adult general population	Yes	Yes/Mild ID (depending on milk intake)	Mild ID	Yes	Mild ID

The ongoing iodization program, regulations, and monitoring and the current iodine sources and iodine status in the normal population are also presented.

Fig. 1 Map of the Nordic countries (except Iceland) in 1960 (55). Dark gray represents mountain areas and striped areas are goiter regions. Sweden still has large areas of goiter 24 years after the start of the iodization program and the salt iodine content was increased in 1966. Goitrous areas are also seen in Norway and Finland.

Fig. 2 Social factors that influenced the goiter frequency in Norway. This is a handwritten note by Carl Schiøtz, who investigated the prevalence of goiter in the Norwegian inland county Hedmark in 1914. In the figure, he indicates the prevalence according to social class: the lowest prevalence was among children of academics, the highest prevalence among farmers not owning their own land (a cotter) (English translation in brackets).

Fig. 3 Goiter as it was first described in Sweden; lecture notes by Per Osbeck that attended one of Carl von Linné's classes, 1746–1747's copy from the Hagströmer Library; Stockholm, Sweden.

Table 2 Comparison of risk populations in the Nordic countries according to available data

Success in risk groups	Iceland	Norway	Denmark	Sweden	Finland
Pregnant women	Sufficient	Mild ID	Mild ID	Mild ID	Unknown To be analyzed
Percentage of pregnant women using iodine-containing multivitamins	Unknown	32%	87%	Unknown To be analyzed	Unknown
Lactating women	Unknown	Unknown	Mild ID	Unknown To be analyzed	Unknown To be analyzed
Percentage of lactating women using iodine-containing multivitamins	Unknown	Unknown	47%	Unknown	Unknown
Children <1 year	To be analyzed	Unknown	Unknown	Unknown	To be analyzed
Adolescents	Sufficient	To be analyzed	Unknown	Unknown study planned	Unknown

This table also illustrates the lack of data (unknown) in several areas in all the countries, but also that several ongoing studies will address some of the lack of knowledge (to be analyzed). The situation during pregnancy is unsatisfactory and none of the countries are aware of an optimal situation during lactation. Data are lacking in small children, and Iceland is the only country with known sufficient levels in adolescents. ID=iodine deficiency.

Kelly F, Snedden WW. Endemic goitre. 1960; Geneva: World Health Organization. Contract No.: 44.

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