Iodine status in the Nordic countries – past and present

REVIEW ARTICLE Iodine s a us in he No dic coun ies  pas and p esen Helena Filipsson Nys o ¨m 1,2 *, Anne Lise B an sæ e 3 , I is E lund 4 , Ingibjo ¨ g Gunna sdo i 5 , Lena Hul he´n 6 , Pe e Lau be g 7,8 , I ene Ma isson 9 , Lone Banke Rasmussen 10 , Su i Vi anen 4,11 and Helle Ma g e e Mel ze 3 1 Ins i u e o Medicine, Sahlg enska Academy, Uni e si y o Go henbu g, Go henbu g, Sweden; 2 Depa men o Endoc inology, Sahlg enska Uni e si y Hospi al, Go henbu g, Sweden; 3 No wegian Ins i u e o Public Heal h, Oslo, No way; 4 Na ional Ins i u e o Heal h and Wel a e, Helsinki, Finland; 5 Uni o Nu i ion Resea ch, Uni e si y o Iceland and Landspi ali Na ional Uni e si y Hospi al, Reykja ik, Iceland; 6 Depa men o Clinical Nu i ion, Sahlg enska Academy, Uni e si y o Go henbu g, Go henbu g, Sweden; 7 Depa men o Endoc inology, Aalbo g Uni e si y Hospi al, Aalbo g, Denma k; 8 Depa men o Clinical Medicine, Aalbo g Uni e si y, Aalbo g, Denma k; 9 Na ional Food Agency, Uppsala, Sweden; 10 Depa men o Endoc inology, Bispebje g Uni e si y Hospi al, Copenhagen, Denma k; 11 School o Heal h Sciences, Uni e si y o Tampe e, Finland Abs ac Backg ound: Adequa e iodine nu i ion is dependen on g ound wa e con en , sea ood, and, as many coun ies use iodized cow odde , dai y p oduc s. In mos coun ies, sal o i ica ion p og ams a e needed o assu e adequa e iodine in ake. Objec i es: The objec i es a e h ee old: 1) o desc ibe he pas and p esen iodine si ua ion in he No dic coun ies, 2) o iden i y impo an gaps o knowledge, and 3) o highligh di e ences among he No dic coun ies’ iodine biomoni o ing and o i ica ion policies. Design: His o ical da a a e compa ed wi h he cu en si ua ion. The No dic coun ies’ s a egies o achie e ecommended in ake and u ine iodine le els and hei espec i e success a es a e e alua ed. Resul s: In he pas , he iodine si ua ion anged om excellen in Iceland o widesp ead goi e and c e inism in la ge a eas o Sweden. The si ua ion was less se e e in No way and Finland. Acco ding o a 1960 Wo ld Heal h O ganiza ion (WHO) epo , he e we e hen no obse a ions o iodine de iciency in Denma k. In Sweden and Finland, he o i ica ion o able sal was in oduced 5075 yea s ago, and in No way and Finland, he o i ica ion o cow odde s a ing in he 1950s helped imp o e he popula ion’s iodine s a us due o he high in ake o milk. In Denma k, iodine has been added o household sal and sal in b ead o he pas 15 yea s. The No dic coun ies di e wi h ega d o egula ions and deg ee o go e nmen al in ol emen . The e a e indica ions ha p egnan and lac a ing women, he wo mos ulne able g oups, a e mildly de icien in iodine in se e al o he No dic coun ies. Conclusion: The No dic coun ies employ di e en s a egies o a ain adequa e iodine nu i ion. The si ua ion is no op imal and is in need o e-e alua ion. Iodine esea che s, No dic na ional ood adminis a ions, and No dic go e nmen al ins i u ions would bene i om collabo a ion o a ain a b oade app oach and gua an ee good iodine heal h o all. Keywo ds: iodine;goi e ;his o y; hy oid; o i ica ion;Iceland;No way;Sweden;Denma k;Finland Recei ed: 18 Ap il 2016; Re ised: 8 May 2016; Accep ed: 9 May 2016; Published: 8 June 2016 Adequa e iodine in ake is necessa y o he no mal p oduc ion o he hy oid ho mones e aio- do hy onine (T4) and iiodo hy onine (T3). In 1952, he Wo ld Heal h O ganiza ion (WHO) s a ed ha in o de o assu e no mal hy oid me abolism, he a e age adul iodine in ake should be 150 mg/day. Low iodine in ake may esul in hypo hy oidism and goi e (1). P egnan and lac a ing women ha e g ea e need o iodine and he ecommended dose is 175250 mg iodine/day o a ge a median u ina y iodine concen a ion (UIC) o 150249 mg/L du ing p egnancy and 100 mg/L du ing lac a ion (25). Thy oid ho mones a e especially impo - an du ing e al li e and ea ly yea s o he de elopmen o he b ain (2, 6, 7). Se e e iodine de iciency (ID) in p egnancy may esul in physical and men al e a da ion  c e inism (8, 9). S udies also indica e ha mode a e o esea ch ood & nu i ion æ Food & Nu i ion Resea ch 2016. #2016 Helena Filipsson Nys o ¨m e al. This is an Open Access a icle dis ibu ed unde he e ms o he C ea i e Commons A ibu ion 4.0 In e na ional License (h p://c ea i ecommons.o g/licenses/by/4.0/), allowing hi d pa ies o copy and edis ibu e he ma e ial in any medium o o ma and o emix, ans o m, and build upon he ma e ial o any pu pose, e en comme cially, p o ided he o iginal wo k is p ope ly ci ed and s a es i s license. 1 Ci a ion: Food & Nu i ion Resea ch 2016, 60: 31969 - h p://dx.doi.o g/10.3402/ n . 60.31969 (page numbe no o ci a ion pu pose) mild ID may impac neu opsychological de elopmen in school-aged child en and impai g ow h and mo o unc- ion (10, 11). A longi udinal s udy in he Uni ed Kingdom showed ha inadequa e ma e nal iodine s a us, assessed by means o UIC in ea ly p egnancy, was associa ed wi h lowe e bal IQ in hei 8-yea -old child en (12). In a simila s udy in Aus alia, mild ID in p egnancy was associa ed wi h lowe educa ional ou comes in child en a age 9 yea s (13). These s udies indica e ha mode a e o mild ID may ha e a long- e m, ad e se impac on e al neu ode elopmen , bu con incing e idence is lacking. Ye , hese indings, as well as epo s ha subop imal iodine in ake is ound in coun ies ha ha e o decades been conside ed iodine-su icien , ha e aised conce ns ha ID is o e looked as a public heal h conce n in de eloped coun ies, including he No dic coun ies (1419). The balance be ween oo li le and oo much iodine The daily iodine in ake is mos ly a sum o he popula- ion’s die a y habi s o ish and o he sea ood, dai y p oduc s (i he cow odde is iodized), he wa e iodine con en , and he cu en iodine o i ica ion p og ams. The single mos impo an iodine issue globally is a oid- ing ID and he esul ing dele e ious consequences o e al and child b ain de elopmen . When a popula ion is li ing unde condi ions o mild ID, he hy oid main ains no mal ho mone p oduc ion, bu compensa ion mecha- nisms esul in goi e and a highe equency o hype hy- oidism wi h au onomous a eas in a oxic mul inodula goi e (TMNG) wi h seconda y heal h consequences (2, 20, 21). When iodine in ake le els a e changed o e ime, his a ec s he incidence and p e alence o hy oid diseases. When a popula ion goes om mode a e o mild ID o no mal iodine le els, he incidence o TMNG dec eases and mo e young people de elop G a es’ disease (GD), as iodine su iciency esul s in an inc eased incidence o au oimmune hy oid disease. The inc eased incidence o GD is p obably empo a y and he incidence o au oimmune hypo hy oidism ises in line wi h iodine le el inc emen s (22). High iodine in ake can gene a e bo h hypo hy oidism and hype hy oidism. Iodine p ophylaxis is he e o e a complex issue ha mus be handled wi h ca e and de ail. Socio- and heal h economic consequences o iodine de iciency The access o iodine a ies in di e en pa s o he wo ld because o di e en le els o iodine in g ound wa e (23) and soils. The use o ish and o he sea ood (24) and o iodine- ich dai y p oduc s (25) a ies and so does he deg ee o iodized sal use. In many a eas wi h iodine-poo soils a om he sea, ID con inues o be a signi ican heal h issue (26). Goi e is he ob ious and isible mani es a ion o ID, bu se e e heal h and socioeconomic consequences a e also appa en h ough o he exp essions o ID: c e inism, neu ological disabili y, men al e a da ion, hypo hy oidism, and TMNG. The e o e, he e m iodine de iciency dis- o de s (IDD) was in oduced in 1983 (27). The e is an associa ion be ween goi e p e alence and he numbe o c e ins bo n. When he goi e p e alence is 3040%, ew c e ins a e bo n, bu i i inc eases o 7080%, 10% o all child en bo n a e c e ins. On a con inuum o con- sequences o men al de elopmen , c e inism is he mos se e e o m. The p e alence o men al e a da ion in ID a eas may exceed he p e alence o c e inism by 10 imes (27), making comba ing IDD he mos cos -e ec i e measu e. Iodine p ophylaxis F om Chinese and Hindu w i ings, we know ha he use o seaweed o comba goi e has been known o housands o yea s and was s ill in use a he beginning o he 19 h cen u y; a e iodine was ound in seaweed in 1811 by Cou ois, he i s p ophylac ic a emp s began in he 1820s. Iodine p ophylaxis was es ablished in 1921 a e Ma ine and Kimball’s classical expe imen in which hey ea ed schoolgi ls in he Uni ed S a es (US) wi h iodine, leading o a d ama ic educ ion in he p e alence o goi e . A e some deba e, iodine p ophylaxis was in oduced in Swi ze land in 1922. In 19231924, iodine o i ica ion o able sal and ap wa e was ied in se e al communi ies in he G ea Lakes egion in he US. O e he ollowing decades, goi e p ophylaxis p og ams we e in oduced wo ldwide (27). In 1986, he In e na ional Council o Con ol o Iodine De iciency Diso de s (ICCIDD) was ounded (27). In 2014, he ICCIDD became he Iodine Global Ne wo k (IGN). The IGN has ini ia ed and imp o ed many iodine p ophylaxis p og ams. The IGN also se s up moni o ing guidelines and encou ages na ional and subcon inen al epo ing. The iodiza ion o sal is he mos commonly used ool o iodine p ophylaxis, bu he amoun o iodine added o able sal a ies om coun y o coun y (27). In de eloping coun ies, he use o iodized oil has been p o en a sa e and easy o m o adminis e ing iodine o he popula ion (28). Manda o y iodine p ophylaxis p og ams a e mo e likely o deli e a sus ained sou ce and, in u n, a public heal h bene i (29). The impo ance o poli ical decisions and con inuous su eillance mus , howe e , be emphasized, all he mo e so due o ac o s such as mig a ion and changes in ood consump ion o e ime. The objec i es o his a icle a e 1) o desc ibe pas and p esen iodine s a us in he i e No dic coun ies, 2) o iden i y impo an gaps o knowledge, and 3) o highligh di e ences be ween he No dic coun ies’ iodine o i ica ion policies ha need o be adap ed o ensu e adequa e iodine s a us in he gene al popula ion and in g oups a isk o ID. Helena Filipsson Nys o ¨m e al. 2 (page numbe no o ci a ion pu pose) Ci a ion: Food & Nu i ion Resea ch 2016, 60: 31969 - h p://dx.doi.o g/10.3402/ n . 60.31969 P esen in es iga ion The i e No dic coun ies Geological and clima ic condi ions o impo ance o in ake le els The e is a cycle o iodine in na u e. Mos iodine esides in he wo ld’s oceans. La ge amoun s o iodine we e leached om su ace soil by glacia ions, snow, and ain and ca ied by i e s and loods in o he sea. The e o e, many moun ainous a eas, bu also lowlands a om he oceans, a e deple ed o iodine (30). Du ing he las Ice Age, he No dic coun ies, Iceland, No way, Denma k, Sweden, and Finland, we e co e ed wi h ice. Iceland is loca ed in he sea on he ansa - lan ic i wi h con inuous olcanic ac i i y. No way and Sweden a e on he same peninsula, wi h moun ain a eas in No way and he no hwes e n pa s o Sweden. The sou h o Sweden is lowland and was pa ly co e ed by he sea when he ice eceded. Finland and Denma k a e sepa a ed om he peninsula by he Bal ic Sea and ha e no moun ain a eas; Denma k and pa s o Finland we e seabed long ago. A e he las Ice Age, app oxima ely 14,000 yea s ago, Denma k was he i s o oday’s No dic coun ies o be popula ed. People la e mig a ed ac oss he na ow sound o sou he n Sweden and o e he No h Sea o sou he n No way. Du ing he Viking age, in he nin h and en h cen u ies AD, No wegians (and I ish) inhab- i ed Iceland. Icelandic, Danish, No wegian, and Swedish people sha e a common gene ic he i age, while Finland was popula ed om he eas , a he i age ha is e iden oday h ough he Finnish language, which is qui e di - e en om ha o he o he No dic coun ies. Howe e , Finland’s majo gene ic in luence is om Eu ope. The Swedish in luence in Finland has been signi ican , bo h gene ically and cul u ally. Geog aphical and clima ic condi ions a o ed animal he ding; in addi ion, he gene o lac ase was p ese ed o e mul iple gene a ions. Milk and dai y p oduc s hus became s aple oods in all he No dic coun ies. Coas al a eas had mo e a o able condi ions and we e he e o e mo e densely popula ed; inland o moun ain a eas we e mo e spa sely popula ed. Fish in ake was high in coas al a eas and a eas o which ish was anspo ed, bu in inland a eas, sal wa e ish, which has highe iodine con en , was a ely consumed. The i e No dic neighbo s employ di e en s a egies o ensu e adequa e iodine in ake (Table 1). Iceland Iceland has been known o i s popula ion’s good iodine s a us. In 1939, Sigu jonsson epo ed indings ha he hy oid gland in he Icelandic popula ion was smalle han was gene ally accep ed in o he coun ies a he ime (31). This was a ibu ed o he uniquely high consump ion o ish, on a e age 200 g/day (32), bu also o high iodine le els in haddock and cod, he mos commonly consumed species (33, 34). Dai y p oduc s a e ano he impo an sou ce o iodine o he Icelandic people (3236), as dai y p oduc s ha e high iodine con en because ish meal is used in cow odde (37). In 1939, he a e age milk in ake was 1 li e /pe son/day, esul ing in an iodine con ibu- ion om ish and dai y p oduc s o 570 mg iodine/pe son/ day (32). In 19781979, he a e age iodine in ake in Iceland was es ima ed o be 336 mg/pe son/day. In a ollow-up s udy, u ina y iodine exc e ion (UIE) was 395 mg/day in men and 270 mg/day in women (38). In 1990, he Icelandic Nu i ion Council epo ed an a e age iodine in ake o 299 mg/pe son/day (32). In ha su ey, o he i s ime, a subg oup ha was po en ially a isk o ID was iden i ied: young women wi h a low in ake o ish and dai y p o- duc s and wi h an iodine in ake in he ange o 86130 mg/ day (32). In many coun ies, iodized sal is he p ima y sou ce o iodine because he in ake o ish and sea ood is low, bu in Iceland, iodized sal is no commonly used and he iodine con en in wa e is low (ISGEM he Icelandic Food Composi ion www1.ma is.is/ISGEM/de ails1.aspx? FAEDA0290 030116) (Table 1). Also, combined wi h a decline in he in ake o p oduc s con aining iodine, he iodine con en in milk has almos hal ed since 1962 (38, 39). This is a ibu able o he educed use o ishmeal in cow odde . Mo e iodine is now added o cow odde , and he added iodine con ibu es mo e o he o al iodine con en o milk oday. The ish meal con en o cow odde a ies be ween 4.4 and 19.4% (40). Young women and hei isk o ID we e u he highligh ed in he Public Heal h Ins i u e o Iceland’s su ey in 2002. The ish in ake in his g oup had dec eased o 40 g/day and milk consump ion had also declined. In a 1990 su ey, young women only ob ained wo- hi ds o he ecommended iodine in ake om hei die (32). Simila ends ha e been obse ed in child en and ado- lescen s (41), also in he las na ional su ey om yea 20102011 (36). Hence, he die o young Icelande s has come o mo e closely esemble he die o he o he No dic coun ies. Iceland exempli ies he agili y o iodine su iciency a he na ional le el and ha he e is a need o ca e ully moni o ends in iodine s a us. I is especially impo an o moni o women o child-bea ing age o secu e heal hy b ain de elopmen in hei child en. No way P io o 1950, he e we e se e al a eas whe e goi e was endemic in No way. In 1917, D Ca l Schiø z des- c ibed his indings o goi e among 10,000 schoolchild en in he inland dis ic o Hedma k (42) (Fig. 1). A he age o 14, he p e alence was 24% among gi ls and 10% among boys (Fig. 2). He ga e a de ailed accoun o c e ins. Iodine in he No dic coun ies Ci a ion: Food & Nu i ion Resea ch 2016, 60: 31969 - h p://dx.doi.o g/10.3402/ n . 60.31969 3 (page numbe no o ci a ion pu pose) Table 1. Compa isons o he No dic coun ies ega ding geological condi ions, iodine le els in wa e , and his o ical da a on iodine in ake le els Iceland No way Denma k Sweden Finland Co e ed by ice du ing Ice Age Yes Yes Yes Yes Yes Ma ine sedimen s No No Yes Sou h Eas e n pa s Sou he n pa s Wa e iodine le el (median) 0.12 mg/L B2mg/L 12.298.3 mg/L (mean) 3.7 mg/L Dug wells: 2.12 ( ange B0.2761) mean 10.7926.8 mg (L D illed wells 3.04 ( ange B0.2232) mean 6.78935.1 mg(L Iodine s a us be o e iodina ion Su icien Se e e o mode a ely de icien Mode a e o mildly de icien Se e ely de icien Mode a ely de icien Deg ee o sea ish in ake du ing 19001950 High High in he coas line low in he inland High in he coas line low in he inland High in he coas line low in he inland High in he coas line low in he inland Fo i ica ion o cow odde his o ically (s a ing poin ) Fish meal used in cow odde olun a y Manda o y om 1950, le el: 2mg/g sal . Volun a y Volun a y Volun a y S a o iodina ion o he popula ion La e 1930s 2000 1936 1946 Type o iodina ion Table sal o household use only Household sal and sal o comme cial b ead p oduc ion Table sal Household sal and cow odde Le el o iodine added 5 mg/g sal 13 mg/g sal 50 mg/g sal 25 mg/g sal Type o legisla ion Volun a y Manda o y Volun a y Volun a y Moni o ing by au ho i ies No No Yes No Some Ac ual cow milk iodine concen a ion (mg/L) 2006: 85283 (a e age 145) Be o e yea 2000: 150 20002012: 100150 20122015: 190 2015: 200 2001: 160 2009: 117 2015: 150 Mean amoun o ish by adul s (g am pe day pe pe son) Na ional die a y su ey in 20102011: ish and sea ood 46 Na ional die a y su ey in 2011: ish and sea ood: 67 ish: 52 Na ional die a y su ey 20112013: 37 Na ional die su ey 20102011 ish and shell ish, women 37, men 43 Na ional die su ey 2012 40 Majo sou ce o iodine in he popula ion Fish Milk Milk and sal Sal Milk Iodine su iciency in he adul gene al popula ion Yes Yes/Mild ID (depending on milk in ake) Mild ID Yes Mild ID The ongoing iodiza ion p og am, egula ions, and moni o ing and he cu en iodine sou ces and iodine s a us in he no mal popula ion a e also p esen ed. Helena Filipsson Nys o ¨m e al. 4 (page numbe no o ci a ion pu pose) Ci a ion: Food & Nu i ion Resea ch 2016, 60: 31969 - h p://dx.doi.o g/10.3402/ n . 60.31969 The well-known goi e dis ic o Modum was ex ensi ely s udied in 19341935 (43) (Fig. 1). The p e alence o goi e was e y high, especially among school child en in he communi y (80%). Also, he p e alence o goi e was highe among subjec s who did no consume ish han among hose who a e ish (43). F om 1950 onwa ds, he iodine o i ica ion o cow odde became manda o y (2 mg/g) o imp o e li es ock ep oduc i e pe o mance (44), a measu e ha esul ed in a d ama ic inc ease in iodine concen a ions in milk and dai y p oduc s in No way. In e es ingly, his was pa alleled in he Uni ed Kingdom (45). In he ein es iga ion o school child en in Modum in 1977, he goi e a e was ound o ha e d opped o 1.5% and goi e was no longe conside ed a p oblem among No wegian child en (46). The su icien iodine in ake was a ibu ed o he high iodine con en o milk, bu also o he ac ha sal wa e ish was mo e widely consumed in he 1970s (46). S udies ca ied ou in men om 10 loca ions sampled in 19711972 (47, 48) and in 1985 poin ed a sa is ac o y UIE; he die a y in ake o iodine o No wegians was sugges ed o be 150250 mg iodine/pe son/day (44). Based on hese publica ions, No wegian heal h au ho i ies ha e since 1950s conside ed No wegians o be iodine- eple e (Table 1). The only s udy ca ied ou so a which has calcula ed he iodine in ake in a ep esen a i e g oup o No wegians was conduc ed in 1997, he NORKOST 2 s udy (49). The mean die a y in ake o iodine was wi hin he ecom- mended dose o men (176 mg/day), while in women he in ake was sligh ly below he ecommended dose (136 mg/ day). Only 7% o he adul popula ion had a daily in ake o iodine below he lowes ecommended in ake le el o 70 mg iodine/day, which is a h eshold o no mal hy oid unc ion. None exceeded 1,000 mg/day. Howe e , i amins and/o mine al supplemen s we e no included in he es ima ions in his s udy. Cu en ly, he la ges s udy o iodine in ake in he wo ld is he No wegian Mo he and Child Coho S udy (MoBa) (19, 50). Iodine in ake om ood and supple- men s was es ima ed using a ood equency ques ion- nai e and alida ed by means o compa ison wi h 24-h UIE in a subsample o 119 pa icipan s (19, 51). O 61,904 women, 16% had an iodine in ake B100 mg/day, 54% had iodine in ake below he No dic ecommenda- ion o 175 mg/day, and only 22% eached he WHO/ UNICEF/ICCIDD ecommenda ion o 250 mg/day. The insu icien iodine in ake le els shown in p egnan women ha e se ala m bells inging a he No wegian Di ec o a e o Heal h, and an Iodine Commi ee is now ying o assess he si ua ion and has been commissioned o p esen p oposals o he alle ia ion o ID in ulne able g oups. In No way, he o i ica ion o sal wi h iodine is olun a y and e y ew b ands con ain iodine. The pe - mi ed le el is 5 mg iodine/g sal , which is oo low o impac he iodine in ake o hose who use his sal . The ood indus y is no allowed o use iodine- o i ied sal in No way. The amoun o iodine in d inking wa e is in luenced by geological condi ions. In samples om 12 di e en si es, he a e age wa e iodine con en was ound o be 1.7 mg/L in 2002. Samples om coas al ci ies had highe concen a ions han samples om inland owns ( ange 0.6 mg/L (Rjukan) o 5.5 mg/L (S a ange ) (Table 1). An inc easing numbe o No wegians ake die a y supple- men s, and oday many mul i i amin-mine al supplemen s Sweden Denma k No way Finland Modum The Swedish Goi e bel Hedma k Fig. 1. Map o he No dic coun ies (excep Iceland) in 1960 (55). Da k g ay ep esen s moun ain a eas and s iped a eas a e goi e egions. Sweden s ill has la ge a eas o goi e 24 yea s a e he s a o he iodiza ion p og am and he sal iodine con en was inc eased in 1966. Goi ous a eas a e also seen in No way and Finland. (Child en wi h academic pa en s) (Fa me s no owing hei own land) Fig. 2. Social ac o s ha in luenced he goi e equency in No way. This is a handw i en no e by Ca l Schiø z, who in es iga ed he p e alence o goi e in he No wegian inland coun y Hedma k in 1914. In he igu e, he indica es he p e alence acco ding o social class: he lowes p e alence was among child en o academics, he highes p e alence among a me s no owning hei own land (a co e ) (English ansla ion in b acke s). Iodine in he No dic coun ies Ci a ion: Food & Nu i ion Resea ch 2016, 60: 31969 - h p://dx.doi.o g/10.3402/ n . 60.31969 5 (page numbe no o ci a ion pu pose) con ain iodine. In he MoBa S udy, 32% o he p egnan women ook iodine-con aining supplemen s which on a e age con ibu ed 100 mg iodine/day o hese women’s die (19). Hence, in No way, he iodine o i ica ion o cow odde had unin ended posi i e e ec s on he human popula ion. Milk, in combina ion wi h he in ake o o he dai y p oduc s, has made his ood ca ego y he majo sou ce o iodine in he No wegian die (49, 52) Howe e , he consump ion o milk, yoghu , and lean ish has declined o e he pas decades in some g oups and explains why subop imal iodine in ake is becoming mo e p e alen in No way (19, 51). Denma k C e inism may de elop when iodine in ake is B25 mg/day, and goi e may appea when iodine in ake is B100 mg/day. Endemic goi e is de ined as ei he goi e ound in 10% o he adul popula ion o ound in 5% among school child en (53). In Denma k, nei he c e inism no endemic goi e has been epo ed in he popula ion. Small local s udies in he 1920s subsequen ly epo ed an incidence o goi e o 15%, bu high goi e equency was no con i med in a na ional s udy o 350,101 Danish school child en pe o med in 19721973 (54). In 1960, Denma k was among he ew coun ies epo ing no endemic goi e (55) and was no , un il ecen ly, conside ed o be an ID a ea. Howe e , when he ocus shi ed om school child en o o he popula ion g oups, he consequences o ID became appa en . Fi s , he incidence a e o TMNG was high wi h clinical and subclinical hype hy oidism pa icula ly common in he elde ly (22). Second, by he end o hei p egnancies, p egnan women did no ha e su icien iodine le els (56). In 1969, he popula ion in Denma k had UIE le els o 64 mg/pe son/day, wi h a ia ions wi hin he coun y (57). Lowe UIE was de ec ed in Ju land, wi h 50 mg/pe son/day han in Zealand wi h 70100 mg/pe son/ day (58). Also, in a na ional Danish die a y su ey om 1985, he a e age in ake was calcula ed o be 114 mg iodine/day (59), which was below he le el o 150 mg/day ecommended by he WHO. A ailable da a in Denma k sugges ed ha he iodine si ua ion had been s able o 35 yea s un il he Minis y o Heal h in Denma k decided o ini ia e a na ionwide iodiza ion p og am in 1997 (53). Be o e he iodiza ion p og am, 27.8% o he popula ion was aking mul i- i amins con aining iodine (53). Iodized sal had been on he Danish ma ke o a long ime (kelp sal able s con aining 1020 mg iodine/g sal ) and, in he 1970s, a leas h ee able sal s con aining iodine we e supplied o he ma ke (iodine con en 1040 mg/g), bu hey only co e ed a ew pe cen poin s o he ma ke . Also, om 1974 un il June 1998, he sale o iodized sal and o he iodized p oduc s was illegal in Denma k, simila o he ban on o he o i ied ood p oduc s wi h no p o en heal h bene i s. Be o e he iodiza ion o sal began, a moni o ing p og am, he Danish In es iga ion o Iodine In ake and Thy oid Diseases (DanThy ), was ini ia ed. The aim was o in es iga e iodine in ake, he p e alence o goi e , and he incidence o hy oid diseases in Aalbo g, wi h mode a e ID, and Copenhagen, wi h mild ID. The main eason o he di e ence in iodine s a us in hese ci ies was di e ences in he wa e iodine con en (60, 61). In Copenhagen, he iodine concen a ion in ap wa e is 19 mg/L, and in Aalbo g, i is 5 mg/L (61). In gene al, wes e n Denma k has lowe wa e iodine concen a ions han hose in eas e n Denma k (Table 1). The in ake o milk ep esen ed 44% o he o al iodine in ake; he in ake o ish accoun ed o 15% o he iodine in ake in he Danish popula ion (62). The mos p ominen de e mi- nan s o high iodine in ake we e he use o mul i i amins con aining iodine, ea ing a leas 200 g ish/week, and ha ing a milk in ake o mo e han 0.5 li e /day (62). The esul s showed ha indi iduals in Aalbo g did no each he ecommended in ake le els e en i hey ollowed he ad ice ega ding in ake o ish and milk. This inding highligh ed ha die a y changes could no ed ess he ID p oblems in Denma k and ha an iodiza ion p og am was needed (62). Fi s , he Danish Ve e ina y and Food Adminis a ion in oduced a olun a y p og am o uni e sal sal iodiza- ion. As his u ned ou o be ine ec i e, i was eplaced in 20002001 by a manda o y p og am o iodine o i ica- ion o household sal and sal in b ead p oduced in Denma k (13 mg iodine/g sal ) (21) (Table 1). E en hough he iodine p og am was cau ious and inc eased he iodine in ake wi h 50 mg/day, he DanThy moni o ing p og am has obse ed e ec s on p e alence o goi e , nodules, and hy oid dys unc ionali y. The incidence o o e hypo hy oidism inc eased mo e in hose a eas ha had p e iously had mild ID han in a eas wi h mode a e ID; he e was a 53% highe incidence o spon aneous (p esumably au oimmune) hypo hy oidism. On he o he hand, in p e iously mode a e ID a eas, he e we e ini ially 49% mo e cases o o e hype hy oidism; howe e , his p o ed a empo a y phenomenon, and he incidence o hype hy oidism is now conside ably below he pe iod- iza ion le el. One phenomenon unde su eillance is whe he GD is becoming mo e common in young people (21, 63). Denma k has demons a ed ha small changes in iodine in ake can ha e d ama ic e ec s on he spec a o hy oid diseases. In he las DanThy moni o ing s udy in 20082010, he UIC le els we e again ound o ha e dec eased (64). The exac eason o his is unknown; he e was no educ ion in he use o mul i i amin supplemen s con- aining iodine, ish in ake, luid in ake, egg consump ion, Helena Filipsson Nys o ¨m e al. 6 (page numbe no o ci a ion pu pose) Ci a ion: Food & Nu i ion Resea ch 2016, 60: 31969 - h p://dx.doi.o g/10.3402/ n . 60.31969 o milk in ake; howe e , he con en o iodine in milk had dec eased. Sweden In Sweden, goi e was i s desc ibed by Ca l on Linne´in 17461747 (65) (Fig. 3) and by he end o he 19 h cen u y, goi e was obse ed among 2030% o he child en in Ga ¨s ikland and Dala na coun ies (66). Twen y yea s la e , he p e alence o goi e had inc eased o 6065% in hese a eas (6770). A na ional in es iga ion was unde - aken in 1929 ha con i med endemic goi e and c e inism in Dala na, Ga ¨s ikland, mid-No land, and in Sma˚land (25, 71, 72) (Fig. 1), a eas a a dis ance om he wes e n seas’ sal y winds (25) and hus a om he p incipal p oduc con ibu ing o iodine in ake: he ing. As he ing was anspo ed o he la ge ci ies (73, 74), u ban popu- la ions and hose li ing along he oads we e well suppo ed (75). Du ing he 19 h cen u y, se e al ac o s con ibu ed o a highe equency o goi e . 1) The in o- duc ion o po a oes o he popula die no only sa ed many om s a a ion bu also led o a less iodine- ich die . 2) The he ing disappea ed o long pe iods. 3) The ise in popula ion mean ha new a eas we e being cul i a ed, a eas ha we e less e ile compa ed wi h he land ha had once been he seabed. The a eas wi h a high incidence o goi e we e known as he goi e bel (Fig. 1), inside o which, he g ound wa e iodine con en may ha e been lowe han in ou side a eas (unpublished obse a ion). The iodiza ion o able sal was in oduced in Sweden in 1936. Ini ially, 10 mg iodine was added pe g am o sal (76), bu in 1966 he amoun was inc eased o 50 mg iodine pe g am o sal (77), as goi e con inued o be p e alen in some a eas (7881) (Table 1). Today, WHO conside s he Swedish popula ion o be iodine-su icien because he popula ion has been subjec o almos li elong iodiza- ion (26, 82, 83). Smalle s udies suppo his assump ion (79, 84, 85), and i was con i med in a na ional s udy in 20062007, in which 889 Swedish school child en aged 612 yea s om 30 schools pa icipa ed (73, 74). Median UIC was 125 mg/L wi h a low p opo ion o child en wi h UIC B100 mg/L and 200 mg/l, indica ing an op imal in ake o iodine (73). Also, he old goi e bel had disappea ed (74). Hypo- and hype hy oidism a e he mos widesp ead o ms o hy oid diseases in Sweden. Au oimmune hypo- hy oidism is common, bu he incidence o hype hy - oidism in Sweden is lowe han he anges indica ed in in e na ional epo s. Se en y- i e pe cen o pa ien s S uma glanulae hy oideae Glandula hy oidea kallas den kö el som sie dä halsen begynne , och ä alld s ö e på ba n än på s o olk, då denna bli Obs ue ad, bli de en s uma, som kalas B oncocele elle s uma …….Dea ä de wi kalla Swei ze halsa , och ä allmän i Swei z, hwilke komme a de as wan, som inne u ö älla ne, och ha någon besynne lig s en a u sig, den wi icke ha oss bekan som ö o dsaka denna sjukdomen. De ä så allmän i Swei z ha jocka halsa , a de le å dem som ha smal hals. Icke komme de a kalkkwane som somlige mena, y då skulle den a a på Go land. Ej helle a k i wane ; y då bo de den wa a gångba i Pa is, icke helle endas a kalla wane , då skulle wå a Lappa ha den me , än någon annan naon. U an dä mås e ges någon s ena i wane , som wi ännu icke we a hwad de ä ö slag. Wo o en s o sak om någon som komme di kunde u ansaka hwad de ä ö en s en som wane hålle . Sjukdomen ä u om Swei z ganska a , och se den sällan hos oss. …. Linneaus ha dock se honom på e unmme hä i Swe ike, som d ucki nog wan. Swei za ne ha många symppaemane hä emo . Bland and a , a de skola gå bo och lå a konungen i F ank ike a på sig. Man obse e a noga, a om de ha en sådan s uma, och d icka mycke he siga d ycke , så kan dä bli k ä we an u a . S uma glanulae hy oideae Glandula hy oidea is he gland called ha is loca ed whe e he neck begins, and i is always la ge in child en han in la ge people, when his is conges ed i will be a goi e , called B oncocele o goi e ???. This is wha we call “Swei ze necks”, and is common in Swi ze land, ha is de i ed om hei wa e , d ained om he moun ains, and ha e some hing peculia in i , ha we do no know and ha causes his disease. I is so equen in Swi ze land o ha e hick necks, ha hey smile a hose wi h hin necks. I is no de i ed om calcium in he wa e as some says, as hey would ha e i in Go land. No ei he om wa e wi h chalk as i would be common in Pa is. Nei he om he cold wa e , as i would be equen among ou same han in any o he naon. I has o be some kind o s one in he wa e , e en hough we do no know wha i is, I would be a la ge issue i somebody could in esga e wha kind o s one ha is in he wa e . Ou side Swi ze land he disease is a e and is seldom seen among us. Linneaus has howe e seen him in a women in Sweden ha has p obably been d inking wa e . The Suisse people may ha e opin- ions agains . Among o he , hey shall le he king in F ance ake i on. I is ca e ully obse ed ha i hey ha e such goi e and d ink a lo o s ong be e ages, a cance can be de eloped. Fig. 3. Goi e as i was i s desc ibed in Sweden; lec u e no es by Pe Osbeck ha a ended one o Ca l on Linne´’s classes, 17461747’s copy om he Hags o ¨me Lib a y; S ockholm, Sweden. Iodine in he No dic coun ies Ci a ion: Food & Nu i ion Resea ch 2016, 60: 31969 - h p://dx.doi.o g/10.3402/ n . 60.31969 7 (page numbe no o ci a ion pu pose) wi h hype hy oidism had GD and he in ensi y o he disease dec eased by age (86, 87). Sweden is a coun y in which se e e ID a oidance elies hea ily on an adequa e iodiza ion p og am which, in u n, equi es a sa is ac o y long- e m moni o ing s a egy. Howe e , he milk iodine concen a ion has dec eased la ely (88) and sal con- sump ion is swi ching om iodized sal o sal wi h no added iodine, highligh ing he need o u u e moni o - ing, especially o ulne able g oups. Finland The i s known obse a ions o goi e in Finland we e made 180 yea s ago in some communi ies in he eas e n pa s o he coun y (89). In 1928, Adle c eu z epo ed ha he wa e iodine con en was low in Finland. The le els we e lowe in eas e n Finland han in he wes , and he e was an in e se associa ion be ween goi e and wa e iodine con en (90). In 1938, Finland was classi ied as a coun y wi h endemic goi e , wi h mos o he disease bu den being ound in eas e n Finland (91) (Fig. 1). In epo s om 19281929, he goi e equency in school child en om some a eas was 1015%, bu in 19531954, i was 3040% in o he s. The mean incidence in all elemen a y Finnish school child en was, howe e , 4.4%. As la e as in he 1950s, he en i e coun y was mode a ely iodine-de icien , also now wi h endemic goi e being obse ed mainly in eas e n Finland. Howe e , he e was conside able discussion abou whe he o he goi ogenic ac o s migh ha e addi ional e ec s on he ID popula- ion in he eas , as iodine in ake le els we e no , in ac , e y di e en . The goi ogenic e ec s o 5- inyl-2- hio- oxazoliodone (VTO, goi in), a hionamid ha blocks he in a hy oidal ho monal syn hesis in milk, was much discussed (27). No dis inc consensus was eached, bu goi ogenic plan s we e e adica ed om he pas u es. Iodized sal was a ailable as ea ly as 1949, bu he use o sal wi h iodine was e y low and he iodine con en in sal was insu icien . Only 20% (o 15 mg) o he iodine in ake came om iodized sal (89, 92). The i s a emp s o in e es he medical au ho i ies in an iodine p ophylaxis p og am we e made in he 1930s and 1940s bu was me wi h li le esponse. In he la e 1950s, a olun a y sal iodiza ion p og am was ini ia ed. In esponse o he ini ia i e o A.I. Vi anen, he S a e Commission o Nu i ion ag eed wi h Finnish packing and impo ing i ms ha only impo o sal con aining 25 mg KI/g would be pe mi ed. The use o iodized sal s eadily inc eased and, in 1969, i was used in 75% o households, eaching 95% o households in 1979. Howe e , he o e all use o sal has dec eased (89) and, in he 1980s, he o i ica ion o able sal ep esen ed only one- hi d o he o al iodine in ake, while he in ake o dai y p oduc s p o ided wo- hi ds o he Finns’ iodine in ake, hanks o he ac i e iodiza ion o li es ock odde (92). In a eas wi h endemic goi e , domes ic animals also su e ed om goi e and ID. A e he decision o iodize able sal and cow odde in Finland in he 1950s (Table 1), milk p oduc ion inc eased (27), along wi h an inc ease o he iodine con en in milk, om 30 mg/L in 1950 o 180 mg/L in he 1970s (89, 93, 94). Dai y p oduc s became he main iodine sou ce (50%) as ea ly as he 1950s. In he 1980s, when he iodine in ake in Finland was 300 mg/d, 60 mg was de i ed om able sal and 200 mg om dai y p oduc s and eggs (27, 93). In he 1980s, he iodine in ake in Finland was he highes in Eu ope (89) and, in 1986, i was s a ed ha he use o iodized sal was no longe necessa y because o he e y ac i e iodiza ion s a egy in household animals (89). A e he iodine p ophylaxis p og am in humans and animals, he equency o goi e declined. In 19651966, he mean p e alence was 0.25% and in he a eas ha had p e iously had he highes p e alence, i was 0.7% (89). O e he cou se o 1520 yea s, he p opo ion o TMNG among pa ien s wi h hype hy oidism dec eased om 80 o 10% (95) and, in he mid-1980s, GD domina ed (89). Fo decades, Finland had a e y e ec i e iodiza- ion s a egy, which es ed hea ily on he iodine con en in dai y p oduc s and iodized sal , and on unchanged consump ion pa e ns. In he las decade o so, iodine le els ha e dec eased in he gene al popula ion o he ex en ha i has esul ed in mild ID (96). Simila ly, a dec ease in milk and iodized sal consump ion is no ed. The e o e, a wo king g oup was ini ia ed wi h ep esen a i es om he Minis y o Heal h and Social A ai s, he Minis y o Ag icul u e, he Finnish Food and D ink Indus ies’ Fede a ion, he Na ional Ins i u e o Heal h and Wel a e, and he Na ional Nu i ion Council o do he necessa y g ound- wo k o new iodine ecommenda ions and ind p ac- ical new solu ions ha could be implemen ed especially by he ood indus y and mass ca e ing se ices. A new ecommenda ion was launched by he Na ional Nu i ion Council in 2015 (96). Finland is an example o a coun y wi h a e y e ec i e iodiza ion s a egy ha elied hea ily on he iodine con en o dai y p oduc s and on un- changed consump ion pa e ns. Iodine s a us in popula ions a isk o ID in he No dic coun ies P egnan women As al eady men ioned, in Iceland, ish and milk in ake has ecen ly dec eased among younge women (32). I is well known ha he in ake o ish and dai y p oduc s is linked o iodine s a us (2527), bu he ecommenda ion o he popula ion o consume ish a leas wice a week and a leas wo po ions o dai y p oduc s daily is based on conce n o bone heal h and ca dio ascula isk (21); iodine s a us was no an issue when he ad ice was issued. Howe e , his ecommenda ion also se es o p omo e Helena Filipsson Nys o ¨m e al. 8 (page numbe no o ci a ion pu pose) Ci a ion: Food & Nu i ion Resea ch 2016, 60: 31969 - h p://dx.doi.o g/10.3402/ n . 60.31969 adequa e iodine in ake. In Iceland, p egnan women in he second and hi d imes e s had UIC 180 mg/L (97), which is wi hin he le els ecommended du ing p egnancy by he WHO (Table 2). Howe e , also he women ha consumed ish and dai y p oduc s below he ecom- mended le els had su icien UIC le els a 160 mg/L, e en i his alue may be ques ioned because o he small size o he sample (97). Hal o he women in his in es- iga ion ook mul i i amins, possibly con aining iodine du ing p egnancy. Mul i i amins wi h o wi hou iodine can be bough , bu gi ing in o ma ion abou iodine is no p io i ized by heal h ca e wo ke s a he Icelandic ma e nal heal h cen e s. As al eady men ioned, a la ge pe cen age o he p egnan women in he No wegian MoBa s udy had insu icien iodine in ake, and only 21.7% eached he WHO/UNICEF/ICCIDD iodine in ake ecommenda ion o 250 mg/day (19, 51). The use o supplemen s con aining iodine was epo ed by 31.6% o mo he s- o-be (Table 2). The p ima y sou ce o iodine om ood was dai y p oduc s, con ibu ing 67% o daily iodine in ake in non-supplemen and 43% in iodine-supplemen use s. The median in ake o iodine om ood was 141 mg/day and he addi ional con ibu ion om supplemen s in iodine- supplemen use s was 107 mg/day. Die a y beha io s associa ed wi h he isk o low and subop imal iodine in ake we e no use o iodine-con aining supplemen s and low in ake o milk/yoghu , sea ood, and eggs (19). A e he in oduc ion o an iodine o i ica ion p o- g am, he si ua ion o Danish women has imp o ed, bu mild o mode a e ID con inues among p egnan women, especially o he women who a e among he 12.7% ha do no ake mul i i amin able s also con aining iodine (98) (Table 2). In Sweden, no speci ic a en ion is gi en o he iodine ques ion du ing p e-na al ca e, as he p egnan popu- la ion in Sweden has appea ed o be iodine-su icien (99, 100). Howe e , ecen ly conce ns ha e a isen ega d- ing he u h o hese assump ions, due o he ollowing ends in Swedish socie y, which a e 1) changes in ood consump ion pa e ns ending o a lowe dai y p o- duc in ake; 2) educed iodine con en in dai y p oduc s (88, 101); 3) a ise in he use o non-iodized sal s, such as lake and gou me sal ; 4) low use o iodized sal in p ocessed oods, p omo ing a lowe iodine in ake in he popula ion; and 5) he sal educ ion p og am launched by he Na ional Food Agency (NFA) o lowe he inci- dence o hype ension. This will a ec p egnan and lac a ing women in pa icula . Re ospec i e local da a ha e ecen ly been published om Uppsala and Ka ls ad showing a median UIC o 99 mg/L in he hi d imes e in 469 women (102), u he unde lining hese assump ions. Young women in Sweden ha e an in ake o ish o 30 g/day, milk 230 g/day, and cheese 25 g/day (103); his may no be enough o co e he inc eased need o iodine. Hence, ID in p egnancy in Sweden may be imminen and he e is an u gen need o moni o ing s udies o enable decision-making on u u e s a egies o ensu e adequa e iodine nu i ion (Table 2). In Finland, he e a e no da a on women du ing p egnancy, bu s udies a e ongoing (Table 2). Lac a ion The e is a la ge knowledge gap ega ding he iodine si ua- ion o mo he s and child en du ing lac a ion in mos No dic coun ies (Table 2). The only coun y wi h a ail- able da a is Denma k. He e, he use o mul i i amins con aining iodine du ing he lac a ion pe iod d ops o almos hal compa ed o he use o such supplemen s du ing p egnancy, alling om 83 o 47%. Rega dless o whe he women ake supplemen s con aining iodine o no , Danish women do no a ain he WHO a ge le els du ing b eas eeding (104). The si ua ion is u he agg a a ed o smoke s, as smoking hal es he milk iodine Table 2. Compa ison o isk popula ions in he No dic coun ies acco ding o a ailable da a Success in isk g oups Iceland No way Denma k Sweden Finland P egnan women Su icien Mild ID Mild ID Mild ID Unknown To be analyzed Pe cen age o p egnan women using iodine-con aining mul i i amins Unknown 32% 87% Unknown To be analyzed Unknown Lac a ing women Unknown Unknown Mild ID Unknown To be analyzed Unknown To be analyzed Pe cen age o lac a ing women using iodine-con aining mul i i amins Unknown Unknown 47% Unknown Unknown Child en B1 yea To be analyzed Unknown Unknown Unknown To be analyzed Adolescen s Su icien To be analyzed Unknown Unknown s udy planned Unknown This able also illus a es he lack o da a (unknown) in se e al a eas in all he coun ies, bu also ha se e al ongoing s udies will add ess some o he lack o knowledge ( o be analyzed). The si ua ion du ing p egnancy is unsa is ac o y and none o he coun ies a e awa e o an op imal si ua ion du ing lac a ion. Da a a e lacking in small child en, and Iceland is he only coun y wi h known su icien le els in adolescen s. IDiodine de iciency. Iodine in he No dic coun ies Ci a ion: Food & Nu i ion Resea ch 2016, 60: 31969 - h p://dx.doi.o g/10.3402/ n . 60.31969 9 (page numbe no o ci a ion pu pose)