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      Gestational changes in iodine status in a cohort study of pregnant women from the United Kingdom: season as an effect modifier 1 2 3

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          Abstract

          Background: Iodine is required throughout pregnancy for thyroid hormone production, which is essential for fetal brain development. Studies of iodine status in pregnant women from the United Kingdom (UK) have focused on early gestation (<16 wk). Data on the effect of advancing gestation on urinary iodine excretion are conflicting, with suggestions of both an increase and a decrease.

          Objectives: The aims were to evaluate iodine status in a cohort of UK pregnant women and to explore how it changes throughout gestation.

          Design: We used samples and data from 230 UK pregnant women who were recruited to the Selenium in PRegnancy INTervention study. Iodine concentration was measured in spot-urine samples that were collected at ∼12, 20, and 35 wk of gestation; creatinine concentration was also measured to correct for urine dilution. A linear mixed model was used to explore the effect of gestational week on iodine-to-creatinine ratio, with change in season, body mass index, daily milk intake, and maternal age controlled for.

          Results: The median urinary iodine concentration from urine samples collected at all time points ( n = 662) was 56.8 μg/L, and the iodine-to-creatinine ratio was 116 μg/g, thus classifying this cohort as mildly-to-moderately iodine deficient. The median iodine-to-creatinine ratios at 12, 20, and 35 wk were 102.5, 120.0, and 126.0 μg/g, respectively. Only 3% of women were taking iodine-containing prenatal supplements. The iodine-to-creatinine ratio increased with advancing gestation, and there was a significant interaction between gestational week and season ( P = 0.026). For a 1-wk increase in gestation, the iodine-to-creatinine ratio increased by a factor of 1.05 (95% CI: 1.02, 1.08) in winter and by a factor of 1.04 (95% CI: 1.00, 1.08) in summer.

          Conclusions: This group of UK pregnant women was mildly-to-moderately iodine deficient at all trimesters, which is of public health concern. The finding that the iodine-to-creatinine ratio increased over the course of gestation may not be generalizable to populations with different iodine status from ours and merits further investigation. This trial was registered at www.isrctn.com as ISRCTN37927591.

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          Most cited references36

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          Iodine deficiency.

          Iodine deficiency has multiple adverse effects in humans, termed iodine deficiency disorders, due to inadequate thyroid hormone production. Globally, it is estimated that 2 billion individuals have an insufficient iodine intake, and South Asia and sub-Saharan Africa are particularly affected. However, about 50% of Europe remains mildly iodine deficient, and iodine intakes in other industrialized countries, including the United States and Australia, have fallen in recent years. Iodine deficiency during pregnancy and infancy may impair growth and neurodevelopment of the offspring and increase infant mortality. Deficiency during childhood reduces somatic growth and cognitive and motor function. Assessment methods include urinary iodine concentration, goiter, newborn TSH, and blood thyroglobulin. But assessment of iodine status in pregnancy is difficult, and it remains unclear whether iodine intakes are sufficient in this group, leading to calls for iodine supplementation during pregnancy in several industrialized countries. In most countries, the best strategy to control iodine deficiency in populations is carefully monitored universal salt iodization, one of the most cost-effective ways to contribute to economic and social development. Achieving optimal iodine intakes from iodized salt (in the range of 150-250 microg/d for adults) may minimize the amount of thyroid dysfunction in populations. Ensuring adequate iodine status during parenteral nutrition has become important, particularly in preterm infants, as the use of povidone-iodine disinfectants has declined. Introduction of iodized salt to regions of chronic iodine deficiency may transiently increase the incidence of thyroid disorders, but overall, the relatively small risks of iodine excess are far outweighed by the substantial risks of iodine deficiency.
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            Assessment of iodine nutrition in populations: past, present, and future.

            Iodine status has been historically assessed by palpation of the thyroid and reported as goiter rates. Goiter is a functional biomarker that can be applied to both individuals and populations, but it is subjective. Iodine status is now assessed using an objective biomarker of exposure, i.e., urinary iodine concentrations (UICs) in spot samples and comparison of the median UIC to UIC cut-offs to categorize population status. This has improved standardization, but inappropriate use of the crude proportion of UICs below the cut-off level of 100 µg/L to estimate the number of iodine-deficient children has led to an overestimation of the prevalence of iodine deficiency. In this review, a new approach is proposed in which UIC data are extrapolated to iodine intakes, adjusted for intraindividual variation, and then interpreted using the estimated average requirement cut-point model. This may allow national programs to define the prevalence of iodine deficiency in the population and to quantify the necessary increase in iodine intakes to ensure sufficiency. In addition, thyroglobulin can be measured on dried blood spots to provide an additional sensitive functional biomarker of iodine status. © 2012 International Life Sciences Institute.
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              Women's dietary patterns change little from before to during pregnancy.

              Principal component analysis (PCA) is a popular method of dietary patterns analysis, but our understanding of its use to describe changes in dietary patterns over time is limited. Using a FFQ, we assessed the diets of 12,572 nonpregnant women aged 20-34 y from Southampton, UK, of whom 2270 and 2649 became pregnant and provided complete dietary data in early and late pregnancy, respectively. Intakes of white bread, breakfast cereals, cakes and biscuits, processed meat, crisps, fruit and fruit juices, sweet spreads, confectionery, hot chocolate drinks, puddings, cream, milk, cheese, full-fat spread, cooking fats and salad oils, red meat, and soft drinks increased in pregnancy. Intakes of rice and pasta, liver and kidney, vegetables, nuts, diet cola, tea and coffee, boiled potatoes, and crackers decreased in pregnancy. PCA at each time point produced 2 consistent dietary patterns, labeled prudent and high-energy. At each time point in pregnancy, and for both the prudent and high-energy patterns, we derived 2 dietary pattern scores for each woman: a natural score, based on the pattern defined at that time point, and an applied score, based on the pattern defined before pregnancy. Applied scores are preferred to natural scores to characterize changes in dietary patterns over time because the scale of measurement remains constant. Using applied scores, there was a very small mean decrease in prudent diet score in pregnancy and a very small mean increase in high-energy diet score in late pregnancy, indicating little overall change in dietary patterns in pregnancy.
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                Author and article information

                Journal
                Am J Clin Nutr
                Am. J. Clin. Nutr
                ajcn
                The American Journal of Clinical Nutrition
                American Society for Nutrition
                0002-9165
                1938-3207
                June 2015
                6 May 2015
                6 May 2015
                : 101
                : 6
                : 1180-1187
                Affiliations
                [1 ]From the University of Surrey, Guildford, United Kingdom (SCB, VF-O, and MPR); Danone Nutricia Early Life Nutrition, Trowbridge, United Kingdom (VF-O); and the Nuffield Department of Obstetrics and Gynecology, University of Oxford, Oxford, United Kingdom (CWGR).
                Author notes
                [3 ]Address correspondence to MP Rayman, Department of Nutritional Sciences, Faculty of Health and Medical Sciences, University of Surrey, Guildford GU2 7XH, United Kingdom. E-mail: m.rayman@ 123456surrey.ac.uk .
                [2]

                The SPRINT (Selenium in PRegnancy INTervention) study was supported by the Wellcome Trust (grant 083918/Z/07/Z). A PhD studentship funded by Wassen International and the Waterloo Foundation covered the costs of laboratory analysis. A Medical Research Council Population Health Scientist Fellowship (MR/K02132X/1) supported SCB during the analysis of the data (including time from the Statistical Services Centre) and writing of the manuscript. This is an open access article distributed under the CC-BY license ( http://creativecommons.org/licenses/by/3.0/).

                Article
                105536
                10.3945/ajcn.114.105536
                4441812
                25948667
                bd1d53ac-73b6-42f4-8683-62239cecb433

                This is an open access article distributed under the CC-BY license ( http://creativecommons.org/licenses/by/3.0/).

                History
                : 15 December 2014
                : 31 March 2015
                Page count
                Pages: 8
                Categories
                Pregnancy and Lactation

                Nutrition & Dietetics
                deficiency,diet,iodine,pregnancy,united kingdom
                Nutrition & Dietetics
                deficiency, diet, iodine, pregnancy, united kingdom

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