Scheffel, Rafael Selbach

Severo, Mateus Dornelles

Revista Brasileira de Ginecologia e Obstetrícia / RBGO Gynecology and Obstetrics

English

Lume 5.8

EditorialDo Brazilian Pregnant Women Need Iodine Supplementation?A Commentary on the Latest American Thyroid AssociationGuidelineGestantes brasileiras precisam de suplementação de iodo? Comentáriosobre a mais recente diretriz da Associação Americana de TireoideMateus Dornelles Severo1 Rafael Selbach Scheffel21Universidade Federal de Santa Maria, Santa Maria, RS, Brazil2Universidade Federal do Rio Grande do Sul, Porto Alegre, RS, BrazilRev Bras Ginecol ObstetIodine is an essential micronutrient required for the pro-duction of thyroid hormones, which are critical for homeo-stasis and neurodevelopment. Because of increased thyroidhormone production, renal iodine excretion and fetal iodinerequirements, dietary iodine requirements are higher inpregnancy than they are for nonpregnant adults.1 Based onthis, the World Health Organization (WHO) and the Ameri-can Thyroid Association (ATA) recommend a daily iodineintake of 250 µg for pregnant and lactating women.2,3Iodine deficiency disorder (IDD) in pregnant women couldresult in harmful effects, including goiter, cretinism, hypo-thyroidism, growth retardation, pregnancy loss, and infantmortality. Moreover, inadequate iodine intake during preg-nancy may lead to neurodevelopmental deficits in offspring,and iodine deficiency is currently considered the leadingpreventable cause of intellectual impairment worldwide.4On the other hand, the excess of iodine may result in fetalgoiter and hypothyroidism. Exposures as minor as thevaginal application of povidone-iodine during delivery orlocal use of disinfectant in newborns can lead to increasedserum TSH concentrations5 and transient neonatalhypothyroidism.6With this information inmind, we readwith great interestthe 2017 Guidelines of the American Thyroid Association forthe Diagnosis and Management of Thyroid Disease duringPregnancy and the Postpartum.7 Among other topics, thenutritional aspects related to iodine sufficiency are ad-dressed in section IV, and a supplementation with 150 μgof potassium iodine per day is suggested on Recommenda-tion 6 for women, in most regions of the world, who areplanning a pregnancyor currently pregnant. This is optimallystarted 3 months in advance of planned pregnancy (strongrecommendation, moderate-quality evidence). Could thisrecommendation improve the quality of the prenatal careof Brazilian pregnant women?The most efficient method of IDD prevention is salt iodin-ation. Also, ongoing monitoring of population biomarkers,such as urinary iodine concentration, is essential to ensurethat population iodine intakes are optimized. In Brazil, the saltiodination is controlled by federal law in partnership withthe National Agency for Sanitary Surveillance (Anvisa, in thePortuguese acronym) and the salt productive sector.8–10 Un-fortunately, dataon the iodine nutritional status are scarce andcontradictory in Brazil. The national project of salt iodination(PNAIsal, in the Portuguese acronym) (which evaluated 477locationsandatotalof18,978school children) identifiedBrazilas a country of “more than appropriate” iodine consumption,with a mean urinary iodine excretion (UIE) concentrationof 276 µg/L.11,12 A recent meta-analysis concluded thatthe majority of the data on this subject are derived from thepopulation in the south/southeast region of Brazil, but theactual overall IDD prevalence is unknown and might still behigh in some areas.13Regarding the pregnant population, three studies werepublished prior to Anvisa's decision to reduce the salt iodineconcentration. In the first one, Barca and cols studied 20 preg-nant women and showed a median UIE of 167.8 μg/L.14The second study evaluated a larger sample (147 women)and observed median UIE of 224 μg/L. The UIE levels rangedfrom 22 μg/L to 534 μg/L, and 29 women (19.6%) had UIEbelow 150 µg/L.15 The third study, published in 2014, evalu-ated 191 pregnant women aged 18 years and with gestationalAddress for correspondenceMateus Dornelles Severo,Universidade Federal de SantaMaria, Avenida Roraima, 1000,prédio 22, 97105-340,Santa Maria, RS, Brazil(e-mail: mateusdsevero@gmail.com).DOI https://doi.org/10.1055/s-0037-1608955.ISSN 0100-7203.Copyright © by Thieme RevinterPublicações Ltda, Rio de Janeiro, BrazilTHIEMEEditorialage up to 14 weeks, and it showed a median UIE of 137.7 µg/L.Interestingly, in this study, 19 (9.9%) pregnant women hadUIE > 250 μg/L, 63 (33%) had UIE within the normal range(150–250 μg/L), and 109 (57.1%) had UIE < 150 μg /L.16So, there is a part of the pregnant womenpopulation that isat risk of IDD and should probably receive supplementation.On the other hand, themajority of the general population andthe pregnant women population, specifically, are iodine suffi-cient, in which case supplementation could induce adverseeffects, such as Wolff-Chaikoff effect and neonatal hypothy-roidism.5 Besides that, the same ATA document suggests500 μg per day as the upper limit of intake of iodine. Consider-ing the Brazilian history of more than appropriate ingestion,supplementationwith 150 μg per daymay be enough to reachthis ceiling, and the pregnant woman and the fetus may beexposed to the effects of excess iodine. Another limiting factoris that UIE, while being an extremely useful tool for assessingthe adequacy of iodine in different populations, does not seemto be a good test for evaluating individuals. Variation in UIEconcentrations is to be expected,when there is day-to-dayandwithin-day variation in iodine intake, especially in iodine-sufficient areas. Due to diurnal variations, random spot UIEconcentrationmeasurement is unlikely to precisely determinethe proportion of a population that has a UIE median concen-tration < 50 μg/L, which indicates iodine deficiency; the datacan only be used to describe the central tendency and thedispersion of UIE concentrations for a particular population.17Lastly, virtually all evidence associating mild to moderateiodine deficiency during gestation with subclinical neuro-logical deficiencies in offspring, such as IQ reduction, comesfrom observational studies.18 To date, no clinical trial hasdemonstrated that iodine supplementation during gestationis capable of ameliorating any robust fetal-maternal outcomeand only surrogate endpoints (thyroid volume, thyroglobulinlevels) were evaluated.19Therefore, we can conclude that the routine supplemen-tation of iodine for every Brazilian pregnant woman is anintervention that needs to be better evaluated. Perhaps,some pregnant women from historically deficient areas ofiodine and without access to iodized salt, as well as someother women with restrictive dietary patterns in salt, grainsand dairy products, may benefit from iodine supplementa-tion because they present a greater risk of severe deficiency,situation in which there is evidence that supplementation iseffective in preventing severe outcomes, such as cretinism.20However, efforts are needed to locate this profile of pregnantwomen within a country with extensive territory and greatcultural diversity, such as Brazil, and to provide appropriatesupplementation.21Conflicts to InterestAuthors declare no conflicts of interest.References1 Glinoer D. The importance of iodine nutrition during pregnancy.Public Health Nutr 2007;10(12A):1542–1546. Doi: 10.1017/S13689800073608862 Andersson M, Aeberli I, Wüst N, et al. The Swiss iodized saltprogram provides adequate iodine for school children and preg-nant women, but weaning infants not receiving iodine-containingcomplementary foods as well as their mothers are iodine defi-cient. J Clin Endocrinol Metab 2010;95(12):5217–5224. Doi:10.1210/jc.2010-09753 Andersson M, de Benoist B, Rogers L. Epidemiology of iodine defi-ciency: Salt iodisation and iodine status. Best Pract Res Clin Endo-crinol Metab 2010;24(01):1–11. Doi: 10.1016/j.beem.2009.08.0054 LaurbergP,CerqueiraC,OvesenL, et al. Iodine intakeasadeterminantof thyroid disorders in populations. Best Pract Res Clin EndocrinolMetab 2010;24(01):13–27. Doi: 10.1016/j.beem.2009.08.0135 Novaes Júnior M, Biancalana MM, Garcia SA, Rassi I, Romaldini JH.Elevation of cord blood TSH concentration in newborn infants ofmothers exposed to acute povidone iodine during delivery. J En-docrinol Invest 1994;17(10):805–808. Doi: 10.1007/BF033477816 Chanoine JP, BoulvainM, Bourdoux P, et al. Increased recall rate atscreening for congenital hypothyroidism in breast fed infantsborn to iodine overloaded mothers. Arch Dis Child 1988;63(10):1207–12107 Alexander EK, Pearce EN, Brent GA, et al. 2017 Guidelines of theAmerican Thyroid Association for the diagnosis andmanagementof thyroid disease during pregnancy and the postpartum. Thyroid2017;27(03):315–389. Doi: 10.1089/thy.2016.04578 Ministry of Health. Department of Health Care. [Technical Manualand Operational Pro-Iodine: National Program for Prevention andControl of Iodine Deficiency Disorders]. Brasília, DF: Ministry ofHealth; 2007. http://www.unicef.org/brazil/pt/iodo_manual.pdf.Accessed February 5, 20179 Federal Law n. 6,150 of 1974December 3: provides formandatoryiodination of salt for human consumption, its control by healthauthorities and other measures. http://www.planalto.gov.br/cci-vil_03/leis/L6150.htm. Accessed February 5, 201710 Ministério da Saúde. Agência Nacional de Vigilância Sanitária.Resolução RDC n. 32, de 25 de fevereiro de 2003. Dispõe sobre o teorde iodo no sal destinado ao consumo humano e dá outras providên-cias. http://portal.anvisa.gov.br/documents/10181/2718376/RDC_32_2003_COMP.pdf/834699ff-bc93-427d-8db2-44ac508db032.Accessed February 5, 201711 Knobel M, Medeiros-Neto G. [Disorders associated to chroniciodine deficiency]. Arq Bras Endocrinol Metabol 2004;48(01):53–61. Doi: 10.1590/S0004-2730200400010000712 Ministério da Saúde. Secretaria de Atenção à Saúde. Departa-mento de Atenção Básica. Coordenação-Geral de Alimentação eNutrição. XIV Reunião Ordinária da Comissão Interinstitucionalpara prevenção e Controle dos Distúrbios por Deficiência de Iodo.Brasília, DF: Ministério da Saúde; 2016. http://189.28.128.100/dab/docs/portaldab/documentos/14_reuniao_iodo.pdf. AccessedAugust 8, 201713 Campos RdeO, Barreto IdosS, Maia LRJ, et al. Iodine nutritionalstatus in Brazil: a meta-analysis of all studies performed in thecountry pinpoints to an insufficient evaluation and heterogene-ity. Arch Endocrinol Metab 2015;59(01):13–22. Doi: 10.1590/2359-399700000000414 Barca MF, Knobel M, Tomimori E, Cárdia MS, Zugaib M, Medeiros-Neto G. Aspectos ultra-sonográficos e prevalência da tireoiditepós-parto em gestantes sem disfunção tireóidea atendidas emhospital público de São Paulo. Arq Bras Endocrinol Metabol 2001;45:180–189. Doi: 10.1590/S0004-2730200100020001015 SoaresR,VanacorR,ManicaD,etal. Thyroidvolumeisassociatedwithfamily history of thyroid disease in pregnant womenwith adequateiodine intake: a cross-sectional study in southern Brazil. J EndocrinolInvest 2008;31(07):614–617. Doi: 10.1007/BF0334561216 Ferreira SM, Navarro AM, Magalhães PK, Maciel LM. Iodine insuffi-ciency in pregnant women from the State of São Paulo. Arq BrasEndocrinol Metabol 2014;58(03):282–287. Doi: 10.1590/0004-2730000002979Rev Bras Ginecol ObstetEditorial17 Soldin OP. Controversies in urinary iodine determinations. ClinBiochem 2002;35(08):575–579. Doi: 10.1016/S0009-9120(02)00406-X18 Bath SC, Steer CD, Golding J, Emmett P, Rayman MP. Effect ofinadequate iodine status in UK pregnant women on cognitiveoutcomes in their children: results from the Avon LongitudinalStudy of Parents and Children (ALSPAC). Lancet 2013;382(9889):331–337. Doi: 10.1016/S0140-6736(13)60436-519 Glinoer D, De Nayer P, Delange F, et al. A randomized trial for thetreatment of mild iodine deficiency during pregnancy: maternaland neonatal effects. J Clin Endocrinol Metab 1995;80(01):258–269. Doi: 10.1210/jcem.80.1.782962320 Boyages SC, Halpern JP, Maberly GF, et al. A comparative study ofneurological and myxedematous endemic cretinism in westernChina. J Clin Endocrinol Metab 1988;67(06):1262–1271. Doi:10.1210/jcem-67-6-126221 Villagelin D, Romaldini JH, Comarella AP, et al. Prenatal vitamincompounds available in brazil are not suitable for adequate iodinesupplementation of pregnant women. Thyroid 2016;26(02):322.Doi: 10.1089/thy.2015.0462Rev Bras Ginecol ObstetEditorial

Do brazilian pregnant women need iodine supplementation? : a commentary on the latest American Thyroid Association Guideline

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Do brazilian pregnant women need iodine supplementation? : a commentary on the latest American Thyroid Association Guideline

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Lume 5.8