Prenatal and Postpartum Maternal Iodide Intake from Diet and Supplements, Urinary Iodine and Thyroid Hormone Concentrations in a Region of the United Kingdom with Mild-to-Moderate Iodine Deficiency.

Diane Threapleton ,Charles J.P Snart,Neil Hancock,Laura J Hardie,Darren C Greenwood,John Wright,Rafaq Azad,Michael Zimmermann,Dan Mason,Paul M Stewart,Ramzi Ajjan,Claire Keeble,Shazia Bi,Samina Ashraf,Dagmar Waiblinger,Nisreen A Alwan ,Janet Cade ,Nigel Simpson ,Sean D Reid ,Kirsten J Cromie ,Elizabeth R Taylor

doi:10.3390/nu13010230

Abstract

Iodine is essential for normal thyroid function, supporting healthy fetal and child development. Iodine requirements increase in pregnancy, but many women in regions without salt iodization have insufficient intakes. We explored associations between iodide intake and urinary iodine concentration (UIC), urinary iodine/creatinine ratio (I/Cr), thyroid stimulating hormone, thyroglobulin, free triiodothyronine, free thyroxine and palpable goiter in a region of mild-to-moderate iodine insufficiency. A total of 246 pregnant women aged 18–40 in Bradford, UK, joined the Health and Iodine in Babies (Hiba) study. They provided detailed information on diet and supplement use, urine and serum samples and were assessed for goiter at around 12, 26 and 36 weeks’ gestation, and 6, 18 and 30 weeks postpartum. Dietary iodide intake from food and drink was estimated using six 24 h recalls. During pregnancy, median (IQR) dietary iodide intake was 101 µg/day (54, 142), with 42% from dairy and 9% from white fish. Including supplements, intake was 143 µg/day (94, 196), with 49% < UK reference nutrient intake (140 µg/day). Women with Pakistani heritage had 129 µg/day (87, 190) median total intake. Total intake during pregnancy was associated with 4% (95% CI: 1%, 7%) higher UIC, 5% (3%, 7%) higher I/Cr, 4% (2%, 6%) lower thyroglobulin and 21% (9%, 32%) lower odds of palpable goiter per 50 µg/day. This cohort consumed less iodide in pregnancy than UK and World Health Organization dietary recommendations. UIC, I/Cr and thyroglobulin were associated with intake. Higher intake was associated with fewer goiters. Because dairy was the dominant source of iodide, women following plant-based or low-dairy diets may be at particular risk of iodine insufficiency.

Highlights

Iodine is essential for normal thyroid function, thyroid-mediated growth and metabolism at all stages of life [1]
Average intakes are presented as geometric means (GEMs) with 95% confidence intervals (CIs) and medians with interquartile ranges (IQRs) to facilitate comparison with WHO definitions
Associations between iodide intake and urinary iodine measures (UIC and iodine/creatinine ratio (I/Cr)) or thyroid hormone and protein concentrations (TSH, Tg, free triiodothyronine (fT3), free thyroxine (fT4) and fT3/fT4 ratio) were explored using linear mixed-effects models to account for repeated measures within individuals, with random slopes for each exposure

Summary

Introduction

Iodine is essential for normal thyroid function, thyroid-mediated growth and metabolism at all stages of life [1]. Severe iodine deficiency has long been associated with detrimental and irreversible consequences for offspring, including hypothyroidism and damage to the developing brain. Iodine deficiency is associated with greater risk of stillbirth, delayed physical development and impaired mental function [3]. Less is known about any consequences for fetal development of mild or moderate deficiency. Associations with smaller birthweight [4,5,6], preterm birth [5] and child neurodevelopment [7,8,9] have been observed in mildly or moderately deficient populations, but evidence is inconsistent, with other large studies reporting no evidence of associations [10,11,12,13]

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