Davidsson, Lena

RERO DOC Digital Library

Invited commentaryAre vegetarians an ‘at risk group’ for iodine deficiency?Iodine deficiency disorders (IDD) are recognized as a majorglobal health problem, in particular in developing countriesbut also in Europe (Delange & Bu¨rgi, 1989; Delange, 1996).The daily intake of iodine varies widely depending ongeographical location and dietary habits. In coastal areas,seafood and iodine-containing mist from the ocean can beimportant sources of iodine while plant and animal productsproduced further inland will contain variable iodine con-tents depending on the geochemical environment. Animalfeeds are often supplemented with iodine in industralizedcountries and, thus, products such as meat, eggs and dairyproducts are important contributors to the dietary iodineintake in the omnivorous diet.A plant-based diet, in particular when based on foodsgrown on soil with low iodine content, can be expected toprovide very limited amounts of iodine. Thus, concern hasbeen raised over iodine intake and status of vegetariansliving in areas with low soil iodine. A recent study made inGermany, a classical iodine-deficient European country,highlights this important issue (Remer et al. 1999).The study by Remer et al. (1999) reports on iodinecontent and urinary iodine excretion monitored in a groupof healthy adults consuming experimental diets (a lacto-vegetarian diet compared with non-vegetarian diets) in arepeated measure design. The results from this studyclearly demonstrate that dietary intake of iodine andurinary iodine excretion were significantly lower withthe lactovegetarian diet compared with mixed diets.Iodine intake, based on analysis of the diets, was verylow from the lactovegetarian diet (about 16 mg/d). How-ever, the analytical data also demonstrate that iodineintake from the non-vegetarian diets was low (35–45 mg/d). For comparison, the current dietary recommendationfor adults is 200 mg iodine/d in Germany (DeutscheGesellschaft fu¨r Erna¨hrung, 1991). Consequently, urinaryexcretion of iodine was low during the entire study: meanvalues were 37 mg/d and 50–61 mg/d during consumptionof the lactovegetarian and mixed diets respectively. Thelow iodine content of the experimental non-vegetariandiets can partly be explained by the fact that fish andseafood were excluded. Furthermore, the contribution ofiodine from beverages in all diets was very limited sinceiodine-free water was consumed during the study and milkproduced in Germany during summer months containsvery little iodine.An important contributor to the total iodine intake inmany countries is iodized table salt. In some countries,iodized salt is also used during manufacture of processedfoods, e.g. bread in the Netherlands, a major source ofdietary iodine in the Dutch diet (Brussard et al. 1997).However, no iodized salt or processed foods with addediodine were included in the experimental diets used byRemer et al. (1999). Thus, the dietary intake of iodineduring this study was representative of the iodine contentof ‘natural’ foodstuffs in the diets. Strict vegetarian diets(vegan diets) which do not include iodine-rich products suchas seaweed, iodized salt or dietary iodine supplements havebeen reported to provide very low quantities of iodine(reviewed by Lightowler & Davies, 1998; Remer et al.1999). However, the study by Remer et al. (1999) demon-strates that lactovegetarian diets, based largely on fruits andvegetables grown on low-iodine soil and containing dairyproducts with low iodine content, will also provide verylittle iodine.Furthermore, the results from this study indicate thatnon-vegetarian diets provide only limited amounts ofiodine when naturally rich sources of iodine such as fishand seafood as well as iodized salt are excluded from thediet. Iodized salt was first introduced in Europe in 1922and is available nationwide in most countries today(Delange, 1996). However, the nutritional impact ofiodized table salt has received renewed attention recently.New data based on urinary excretion which indicate adecline in iodine intake have been reported from school-children in Switzerland (Zimmermann et al. 1998) andblood donors in New Zealand (Thomson et al. 1997).Results from these studies suggest that iodine status mayno longer be adequate in the population groups studied.Possible reasons for the decreased iodine intake includechanged dietary habits and reduced table salt intake as apositive response to health guidelines.Thus, low dietary intake of iodine is of concern invegetarians and, clearly, different possibilities for increas-ing the iodine intake in vegetarian diets need to be con-sidered. However, low intake of iodine can also be apotential problem in larger segments of the population.The recent studies in Switzerland and New Zealand demon-strate the importance of monitoring iodine intake in indus-trialized countries and indicate a need for re-evaluation offortification levels of iodized table salt.Although the consequences of manifest IDD are wellknown (goitre, impaired reproductive outcome, as well asmental and physical retardation), the subclinical effects oflow iodine intake and the physiological significance of lowiodine excretion need to be studied further.Lena DavidssonLaboratory for Human NutritionSwiss Federal Institute of TechnologyPO Box 474CH-8803 Ru¨schlikonSwitzerlandBritish Journal of Nutrition (1999), 81, 3–4 3https:/www.cambridge.org/core/terms. https://doi.org/10.1017/S0007114599000069Downloaded from https:/www.cambridge.org/core. University of Basel Library, on 10 Jul 2017 at 16:02:21, subject to the Cambridge Core terms of use, available atReferencesBrussard JH, Brants HAM, Hulshof KFAM, Kistemaker C &Lo¨wik MRH (1997) Iodine intake and urinary excretionamong adults in the Netherlands. European Journal of ClinicalNutrition 51, S59–S62.Delange F (1996) Iodine nutrition in Europe, an update 1996. InThe Thyroid and Iodine. Proceedings of the Merck EuropeanThyroid Symposium, pp. 31–41 [J Nauman, D Glinor, LEBraverman and U Hostalek, editors]. Stuttgart: FK Schattauer.Delange F & Bu¨rgi H (1989) Iodine deficiency disorders in Europe.Bulletin of the World Health Organization 67, 317–325.Deutsche Gesellschaft fu¨r Erna¨hrung (1991) Empfehlungen fu¨r dieNa¨hrstoffzufuhr (Recommendations for Nutrient Intakes).Frankfurt/Main: Bro¨nners Druckerei.Lightowler HJ & Davies J (1998) Iodine intake and iodinedeficiency in vegans as assessed by the duplicate portiontechnique and urinary iodine excretion. British Journal ofNutrition 80, 529–535.Remer T, Neubert A & Manz F (1999) Increased risk of iodinedeficiency with vegetarian nutrition. British Journal of Nutrition81, 45–49.Thomson CD, Colls AJ, Conaglen JV, Macormack M, Stiles M &Mann J (1997) Iodine status of New Zealand residents asassessed by urinary iodide excretion and thyroid hormones.British Journal of Nutrition 78, 901–912.Zimmermann MB, Hess S, Zeder C & Hurrell RF (1998) Urinaryiodine concentrations in Swiss schoolchildren from the Zu¨richarea and the Engadine valley. Swiss Medical Weekly 128, 770–774.q Nutrition Society 19994 L. Davidssonhttps:/www.cambridge.org/core/terms. https://doi.org/10.1017/S0007114599000069Downloaded from https:/www.cambridge.org/core. University of Basel Library, on 10 Jul 2017 at 16:02:21, subject to the Cambridge Core terms of use, available at

Are vegetarians an ‘at risk group' for iodine deficiency?

Abstract

Similar works

Full text

Available Versions

RERO DOC Digital Library