Similarities and differences of dietary and other determinants of iodine status in pregnant women from three European birth cohorts
As a component of thyroid hormones, adequate iodine intake is essential during pregnancy for fetal neurodevelopment. Across Europe, iodine deficiency is common in pregnancy, but data are lacking on the predictors of iodine status at this life stage. We, therefore, aimed to explore determinants of iodine status during pregnancy in three European populations of differing iodine status.
Data were from 6566 pregnant women from three prospective population-based birth cohorts from the United Kingdom (ALSPAC, n = 2852), Spain (INMA, n = 1460), and The Netherlands (Generation R, n = 2254). Urinary iodine-to-creatinine ratio (UI/Creat, µg/g) was measured in spot-urine samples in pregnancy (≤ 18-weeks gestation). Maternal dietary intake, categorised by food groups (g/day), was estimated from food-frequency questionnaires (FFQs). Multivariable regression models used dietary variables (energy-adjusted) and maternal characteristics as predictors of iodine status.
Median UI/Creat in pregnant women of ALSPAC, INMA, and Generation R was 121, 151, and 210 µg/g, respectively. Maternal age was positively associated with UI/Creat in all cohorts (P < 0.001), while UI/Creat varied by ethnicity only in Generation R (P < 0.05). Of the dietary predictors, intake of milk and dairy products (per 100 g/day) was positively associated with UI/Creat in all cohorts [ALSPAC (B = 3.73, P < 0.0001); INMA (B = 6.92, P = 0.002); Generation R (B = 2.34, P = 0.001)]. Cohort-specific dietary determinants positively associated with UI/Creat included fish and shellfish in ALSPAC and INMA, and eggs and cereal/cereal products in Generation R.
The cohort-specific dietary determinants probably reflect not only dietary habits but iodine-fortification policies; hence, public-health interventions to improve iodine intake in pregnancy need to be country-specific.
KeywordsIodine Pregnancy Diet Determinants Milk and dairy products ALSPAC
The Avon Longitudinal Study of Parents and Children
Body mass index
Certified reference material
INfancia y Medio Ambiente
Relative standard deviation
Standard error of estimate
Semi-quantitative food-frequency questionnaire
Urinary iodine-to-creatinine ratio
Urinary iodine concentration
World Health Organisation
EUthyroid project: This project has received funding from the European Union´s Horizon 2020 research and innovation programme under Grant agreement no. 634453.
ALSPAC: We are extremely grateful to all the families who took part in this study, the midwives for their help in recruiting them, and the whole ALSPAC team, which includes interviewers, computer and laboratory technicians, clerical workers, research scientists, volunteers, managers, receptionists and nurses. The UK Medical Research Council and Wellcome (Grant ref.: 102215/2/13/2) and the University of Bristol provide core support for ALSPAC. This publication is the work of the authors and Dr Bath will serve as a guarantor for the contents of this paper. ALSPAC data collection is funded from a wide range of sources, a comprehensive list of which is available on the ALSPAC website (http://www.bristol.ac.uk/alspac/external/documents/grant-acknowledgements.pdf). The existing iodine measurements in ALSPAC were funded from (1) the NUTRIMENTHE project, which received a research grant from the European Community’s 7th Framework Programme (FP7/2008–2013) under grant agreement 212652 and (2) a Ph.D. studentship that was funded by Wassen International and the Waterloo Foundation (2009–2012). We would like to thank Dr Pauline Emmett for helping with the dietary analysis of the ALSPAC food-frequency questionnaire.
Generation R: The Generation R Study is conducted by the Erasmus Medical Center in close collaboration with the Faculty of Social Sciences of the Erasmus University Rotterdam, the Municipal Health Service Rotterdam area, Rotterdam, and the Stichting Trombosedienst & Artsenlaboratorium Rijnmond (STAR-MDC), Rotterdam. The Generation R Study is supported by the Erasmus Medical Center, Rotterdam, the Erasmus University Rotterdam, The Netherlands Organization for Health Research and Development (ZonMw), The Netherlands Organization for Scientific Research (NWO), the Ministry of Health, Welfare and Sport. A grant from the Sophia Children’s Hospital Research Funds supports the neurodevelopmental work on thyroid; Robin P. Peeters is supported by a clinical fellowship from ZonMw, project number 90700412.
INMA: This study was funded by grants from UE (FP7-ENV-2011 cod 282957 and HEALTH.2010.2.4.5-1) and Spain: Instituto de Salud Carlos III (Red INMA G03/176; CB06/02/0041; FIS-FEDER: PI041436, PI05/1079, PI06/0867, PI081151, FIS-and PS09/00090, PI11/01007, PI11/02591, PI11/02038, PI13/1944, PI13/2032, PI14/00891, PI14/01687, and PI16/1288; Miguel Servet-FEDER CP11/00178, CP15/00025, and CPII16/00051, MS13/00054), Generalitat Valenciana: FISABIO (UGP 15-230, UGP-15-244, and UGP-15-249), Generalitat de Catalunya-CIRIT 1999SGR 00241, Fundació La marató de TV3 (090430), Department of Health of the Basque Government (2005111093 and 2009111069), and the Provincial Government of Gipuzkoa (DFG06/004 and DFG08/001).
MD performed statistical analyses, interpreted the data, and wrote the first version of the manuscript. MPR, SCB, RPP, TIMK, MG, and DL contributed to statistical analyses, interpretation of the data, and writing of the manuscript. JV, LG, ME, JI, and JS helped with writing of the manuscript. All authors read and approved the final manuscript.
Compliance with ethical standards
Conflict of interest
The authors declare that they have no conflict of interest.
All studies in these analyses have been approved by the appropriate ethics committees and have, therefore, been performed in accordance with the ethical standards laid down in the 1964 Declaration of Helsinki and its later amendments. Detailed information is included as part of the main text (see “Methods”, sub-section “Ethics”).
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