Agostinho Almeida

Edgar Pinto

Elisa Keating

Frontiers in Nutrition

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TYPE EditorialPUBLISHED 15 August 2023DOI 10.3389/fnut.2023.1260834OPEN ACCESSEDITED AND REVIEWED BYEllen E. Blaak,Maastricht University, Netherlands*CORRESPONDENCEEdgar Pintoecp@ess.ipp.ptRECEIVED 18 July 2023ACCEPTED 31 July 2023PUBLISHED 15 August 2023CITATIONKeating E, Pinto E and Almeida A (2023)Editorial: Iodine in health and disease.Front. Nutr. 10:1260834.doi: 10.3389/fnut.2023.1260834COPYRIGHT© 2023 Keating, Pinto and Almeida. This is anopen-access article distributed under the termsof the Creative Commons Attribution License(CC BY). The use, distribution or reproductionin other forums is permitted, provided theoriginal author(s) and the copyright owner(s)are credited and that the original publication inthis journal is cited, in accordance withaccepted academic practice. No use,distribution or reproduction is permitted whichdoes not comply with these terms.Editorial: Iodine in health anddiseaseElisa Keating 1,2, Edgar Pinto 3,4* and Agostinho Almeida31Unit of Biochemistry, Department of Biomedicine, Faculty of Medicine, University of Porto, Porto,Portugal, 2CINTESIS@RISE, Faculty of Medicine, University of Porto, Porto, Portugal, 3REQUIMTE/LAQV,Department of Chemical Sciences, Faculty of Pharmacy, University of Porto, Porto, Portugal,4Department of Environmental Health, ESS, Polytechnic of Porto, Porto, PortugalKEYWORDSiodine, iodine deficiency, iodine excess, childhood, pregnancy, thyroid hormonesEditorial on the Research TopicIodine in health and diseaseIodine is an essential micronutrient, used by the thyroid gland to synthesize thyroidhormones that perform pleiotropic functions in the human organism. These rolesinclude stimulating somatic growth and regulating metabolism, cardiac function (1), andneurodevelopment, the latter through the control of synapse formation, neuronal migration,and myelination (2).Iodine is supplied by food sources in several chemical forms: iodide (I−) and iodate(IO3−), generally in the form of sodium or potassium salts, molecular iodine (I2), andmonoatomic iodine in association with proteins, the so-called organic iodine (3).Natural food sources of iodine include seafood, dairy products, and eggs. However, thesefood sources may contribute differently to iodine intake, depending on the frequency ofconsumption but also on geological and climatic conditions and specific livestock practicesin different regions of the world (4).Additionally, artificial sources of iodine include iodized salt and food supplements,which provide potassium or sodium iodide or potassium iodate.The extreme importance of iodine throughout the life cycle is evidenced by a set ofdiseases that result from iodine deficiency (the iodine deficiency disorders, IDD) and theconsequent inadequate production of thyroid hormones.The consequences of iodine deficiency largely depend on the stage of the life cycleand also on the severity of the iodine deprivation. For example, during pregnancy, severeiodine deficiency results in severe mental and growth impairments associated with deaf-mutism and spasticity (all features of cretinism); on the other hand, mild-to-moderateiodine deficiency in utero is associated with impairments in neurodevelopment revealed bya decreased intelligence quotient, impairment in fine motor skills, and also in verbal andnon-verbal communication skills (5, 6).The inadequate intake of iodine is currently a worldwide problem because, as alreadymentioned, the natural availability of this element depends on a series of geographical,geological, and climatic factors that escape direct human action.The oceans are the largest reservoirs of iodide that, once transformed into elementaliodine, follows the water cycle and is supplied to the soil through rain. However, the iodinecontent of soils, and therefore of food crops, is greatly diminished due to rain leaching inareas of high rainfall. Soils deficient in iodine and, consequently, nutritional iodine deficiencyare therefore more common in mountainous inland areas with high precipitation rates(6), but this deficiency is also detected in very rainy coastal zones, such as the Azoresislands, Portugal.Frontiers inNutrition 01 frontiersin.orgKeating et al. 10.3389/fnut.2023.1260834All these conditions underlie the existence of endemic areas foriodine deficiency and the high global prevalence of IDD, regardlessof the degree of local socioeconomic development.In this context, the prevention of IDD through the promotionof adequate iodine intake was a global public health objectiveduring the 1990s, motivating the WHO and UNICEF torecommend universal salt iodization. Recent data reveal that thisstrategy resulted in a decrease in the number of countries withiodine deficiency from 113 in 1993 to 20 in 2017 (7).While iodine replenishment through salt iodization programsor iodine supplementation in populations with severe iodinedeficiency has been shown to be effective in preventing IDD,this may not be the case in populations with mild-to-moderateiodine deficiency. On the other hand, these strategies have alsoprecipitated the occurrence of circumstances of excessive iodineintake (8).Despite all this, iodine deficiency in pregnant women remainsprevalent. For example, in 2015, Zimmermann et al. reported thatpregnant women in about 2/3 of European countries were iodinedeficient (9).The purpose of this Research Topic was to collect recentupdates related to the role of iodine in health and disease. Itincludes four articles that address different aspects of this topic.One emphasizes the occurrence of widespread iodine deficiencyduring pregnancy (2019 data), particularly in women not takingiodine supplements in Jiangsu Province, China. In this Chineseprovince, the average iodine content of iodized salt for householdusage was lowered in 2012 due to concerns about excessive iodineintake. In this same paper, Wang et al. report that urinary iodineconcentration (UIC) below 100 µg/L, corresponding to moderate-to-severe iodine deficiency, in the first trimester of pregnancy isassociated with an increased risk of subclinical hypothyroidismlater in pregnancy among euthyroid women.On the other side of the iodine status spectrum, Candido et al.aimed to build a theoretical model that could estimate iodineintake from all food sources in childhood and pregnancy in aregion of Brazil, a country with a history of excessive iodineintake resulting from excessive iodized salt consumption. Thistheoretical model, based on a healthy diet, estimated that dailyintake of iodine by schoolchildren and pregnant women exceeds therecommendations. The authors propose that the developed modelcould be used to guide public policies formanaging the population’siodine status.Importantly, in addition to concerns about iodine deficiencyand iodine excess updated by Wang et al. and Candido et al.,respectively, Remer highlights, in an opinion article, the possibilitythat the increase in TSH levels as a result of improved iodinenutrition in populations with mild-to-moderate iodine deficiencyis of a physiological rather than pathophysiological nature andthat a general misinterpretation of these higher TSH levels hasbeen documented, contributing to the probable over-prescriptionof thyroxine. This may motivate the search for new TSH referencevalues according to iodine status.Lastly, Liu et al. propose that aging alters immune andinflammatory responses, as well as the mitochondrial function andcytochrome P450 metabolism of the thyroid gland, emphasizingthat iodine replacement measures can differentially affect thepopulation according to the life cycle stage.Overall, the articles included in this Research Topic highlightthat iodine deficiency or excess remain major public health issuesthat require close country- and life cycle stage-specific monitoring.Author contributionsEK: Writing—original draft. EP: Writing—review and editing.AA: Writing—review and editing.Conflict of interestThe authors declare that the research was conducted in theabsence of any commercial or financial relationships that could beconstrued as a potential conflict of interest.The author(s) declared that they were an editorial boardmember of Frontiers, at the time of submission. This had no impacton the peer review process and the final decision.Publisher’s noteAll claims expressed in this article are solely those of theauthors and do not necessarily represent those of their affiliatedorganizations, or those of the publisher, the editors and thereviewers. Any product that may be evaluated in this article, orclaim that may be made by its manufacturer, is not guaranteed orendorsed by the publisher.References1. ShahidMA, Ashraf MA, Sharma S. Physiology, Thyroid Hormone. Treasure Island,FL: StatPearls Publishing (2023).2. Velasco I, Bath SC, Rayman MP. Iodine as essential nutrient during the first 1000days of life. Nutrients. (2018) 10:290. doi: 10.3390/nu100302903. Patrick L. Iodine: deficiency and therapeutic considerations. Altern Med Rev.(2008) 13:116–27.4. Number of food vehicles with selected nutrients in country standards. TheNumber of Food Vehicles in a Country for Which Official Documentation Exists thatSpecifies the Nutrients to be Added in Fortification. (2021). Available online at: https://fortificationdata.org (accessed February 19, 2021).5. Bath SC. The effect of iodine deficiency during pregnancy on child development.Proc Nutr Soc. (2019). 78:150–60. doi: 10.1017/S00296651180028356. Eastman CJ, Zimmermann MB. The iodine deficiency disorders. In: Feingold KR,Boyce A, Blackman M, Boyce A, Chrousos G, Corpas E, et al., editor. Endotext. SouthDartmouth, MA: Mdtext.com, Inc. (2018).7. Zhao W, Li X, Xia X, Gao Z, Han C. Iodine nutrition duringpregnancy: past, present, and future. Biol Trace Elem Res. (2019)188:196–207. doi: 10.1007/s12011-018-1502-z8. Pearce EN, Andersson M, Zimmermann MB. Global iodine nutrition:where do we stand in 2013? Thyroid. (2013) 23:523–8. doi: 10.1089/thy.2013.01289. Zimmermann MB, Gizak M, Abbott K, Andersson M, Lazarus JH. Iodinedeficiency in pregnant women in Europe. Lancet Diab. Endocrinol. (2015) 3:672–4. doi: 10.1016/S2213-8587(15)00263-6Frontiers inNutrition 02 frontiersin.org

Editorial: Iodine in health and disease

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Editorial: Iodine in health and disease

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