In childhood, diets high in sodium and low in potassium contribute to raised blood pressure and cardiovascular disease later in life(1). For New Zealand (NZ) children, bread is a major source of dietary sodium, and fruit, vegetables, and milk are major dietary sources of potassium(2,3). However, it is mandatory to use iodised salt in NZ bread meaning reducing the salt and thus sodium content could put children at risk of iodine deficiency(4). Our objective was to measure the sodium, potassium, and iodine intake, and blood pressure of NZ school children 8-13 years old. A cross-sectional survey was conducted in five primary schools in Auckland and Dunedin. Primary schools were recruited between July 2022 and February 2023 using purposive sampling. Seventy-five children (n= 37 boys, 29 girls, and nine children who did not state their gender) took part. The most common ethnicity was NZ European and Other (n=54 or 72%) followed by Māori (indigenous inhabitants; n=9 or 12%) and Pasifika (n=5 or 7%). The main outcomes were 24-hour sodium and potassium intake, sodium to potassium molar ratio, 24-hour iodine intake, and BP. Sodium, potassium, and iodine intake were assessed using 24-hour urine samples and BP was assessed using standard methods. Differences by gender were tested using two-sample t-tests and nonparametric Wilcoxon two-sample tests. The mean (SD) 24-hour sodium excretion, potassium excretion, and sodium to potassium molar ratio for children with complete samples (n=59) were 2,420 (1,025) mg, 1,567 (733) mg, and 3.0 (1.6), respectively. The median (25th, 75th percentile) urinary iodine excretion was 88 (61, 122) µg per 24 hours and the mean (SD) systolic and diastolic blood pressure (n=74) were 105 (10) mmHg and 67 (9) mmHg, respectively. There was a significant difference between boys and girls for iodine (77 (43, 96) vs. 98 (72, 127) µg per 24 hours; p=0.02) but no other outcomes. In conclusion, children consumed more sodium and less potassium and iodine than World Health Organization recommendations(5). However, future research should confirm these findings in a nationally representative sample. Evidence-based, equitable interventions and policies with adequate monitoring should be considered to reduce potentially suboptimal sodium, potassium, and iodine intakes in New Zealand.

Current food systems pose risks to both population and environmental health. Reducing the intake of animal-based foods, such as dairy products, and increasing consumption of plant-based foods align with priorities for addressing climate change and promoting overall health. Plant-based alternatives to cow’s milk can be readily substituted for cow’s milk without altering meal patterns and food habits, making them a popular choice among those reducing animal-product consumption. However, plant-based milk alternatives do not necessarily provide the same nutrients as cow’s milk, particularly essential micronutrients like iodine. While national data indicate that the UK is iodine-replete, certain population subgroups (such as pregnant women, women of reproductive age, and vegans) remain at risk of iodine deficiency. Young women are more likely than other age groups to consume plant-based milk alternatives, heightening public health concerns about iodine insufficiency in this demographic. Current consumers of plant-based milk alternatives in the UK have lower iodine intake and status compared to consumers of cow’s milk. Population-level effects of replacing milk with plant-based alternatives vary and depend on factors such as the role of plant-based milk alternatives in the diet (i.e. in addition to, or as a replacement for milk), the presence of other iodine sources in the diet, the consumer’s life stage, and whether the alternatives are fortified with iodine. This review examines the literature on plant-based milk alternatives and iodine intake, focusing on implications of this dietary shift and strategies to improve iodine intake in those opting for plant-based milk alternatives in the UK population.

Plant-based diets, with limited quantities of animal foods, are increasingly promoted for sustainability and health. In many countries, animal-source foods provide the majority of several micronutrients at a population level; in the UK, milk and dairy products contribute around one third of total calcium, vitamin B12 and iodine intake in adults. Recommendations for a predominantly plant-based diet may have the unintended consequence of reducing intake of micronutrients, particularly in groups with an already-low intake of these nutrients, such as women of reproductive age. Furthermore, young women are the group most likely to replace dairy products with plant-based alternatives. Milk alternatives are often fortified to match the nutrient content of cows’ milk for some micronutrients (e.g. calcium), but not of others (e.g. iodine or vitamin B2). Unfortified alternatives have an iodine concentration that is just 2 % of that of UK cows’ milk, and the rise in popularity of these products may increase iodine-deficiency risk in consumers. Low nutrient intake is of concern prior to, and during, pregnancy, when many of the micronutrients at risk (iron/calcium/iodine) are essential for foetal development. While there may be awareness of some at-risk nutrients on a plant-based diet, this may not be the case for all. At-risk nutrients should be considered in nutrition guidelines and advice given by healthcare professionals to ensure that the diets are well planned and supplemented when necessary. This review focuses on the provision of micronutrients (particularly iodine) from plant-based diets in the UK.

This article explores how the models of medical risk from radiation established in the aftermath of the nuclear attacks on Hiroshima and Nagasaki are insufficient for understanding the risks faced by people in contaminated environments like Fukushima. These models focus exclusively on levels of external radiation, while the risk faced by people in areas affected by radioactive fallout comes from internalizing fallout particles. These models have helped to obscure the health impacts over the last 76 years of those exposed to fallout, from the people who experienced the Black Rain in Hiroshima, to the global hibakusha exposed through nuclear testing, production and accidents, and now to those living where the plumes deposited radiation in Fukushima.

Breast milk (BM) is the only source of iodine and bioactive compounds that influence growth and development in infants. The content of BM may be influenced by maternal body mass index (BMI). The aim of this study was to investigate the effect of maternal weight on BM and cord blood iodine concentrations, growth-related hormones, infant anthropometric measurements. A total of 84 mother-infant pairs participated. Levels of leptin, adiponectin and insulin-like growth factor-I (IGF-I) in postnatal BM and cord blood were analysed by enzyme-linked immunosorbent assay (ELISA), iodine by Sandell-Kolthoff reaction. Dietary iodine intake of women was determined by food frequency questionnaire, and anthropometric measurements of infants at birth and 3 months were evaluated. Dietary iodine intake was found to be similar in normal weight (NW) and overweight/obese (OW/OB) women (p > 0.05). Breast milk iodine concentration (BMIC) was 17.4 μg in NW, 18.2 μg in OB/OW women. Adiponectin in cord blood and IGF-I in BM were higher OB/OW than NW women (p < 0.05). Positive correlations were found between the infant birth weight and adiponectin in BM, between the infant body weight at 3 months and leptin and adiponectin in BM, between the infant birth head circumference and IGF-I in BM (p < 0.05). In multiple linear regression model, leptin and adiponectin in BM had a positive effect on infant body weight (p < 0.05). Maternal BMI may influence infant body weight via leptin and adiponectin in BM and infant head circumference via IGF-I. No relationship was found between maternal BMI and iodine levels and anthropometric measurements of the infant. Longitudinal studies are recommended to understand the effect of BMIC on growth.

Depression has been associated with subclinical hypothyroidism and altered hypothalamic-pituitary-thyroid axis functioning. Adequate iodine nutrition is essential for healthy thyroid functioning. We therefore determined associations of iodine and thyroid status with paediatric major depressive disorder (pMDD) among Swiss adolescents and explored whether associations are sex-specific and mediated by stress. We conducted a matched case–control study in 95 adolescents with diagnosed pMDD and 95 healthy controls. We assessed depression severity using the Children’s Depression Rating Scale-Revised and stress using the perceived stress scale (PSS) and measuring hair cortisol levels. We determined iodine status by measuring urinary iodine concentrations (UIC) and thyroid status by thyroid-stimulating hormone (TSH) and free thyroxine (FT4) in serum. Median (IQR) UIC did not differ between cases (121 (87, 174) µg/l) and controls (114 (66, 183) μg/l, P = 0·3). Median TSH and FT4 were lower in cases than controls (TSH: 1·36 (0·91, 2·00) mlU/l v. 1·50 (1·18, 2·06) mlU/l, P = 0·039; FT4: 14·7 (12·9, 16·9) pmol/l v. 15·7 (14·3, 17·2) pmol/l, P = 0·004). The prevalence of hypothyroxinaemia (normal TSH; low FT4) was higher among female cases than controls (21 % v. 4%, P = 0·006). PSS scores were higher while hair cortisol was lower in cases than controls (PSS: 25 (20, 28) v. 11 (7, 15), P < 0·001; cortisol: 2·50 (1·34, 3·57) pg/mg v. 3·23 (1·79, 4·43) pg/mg, P = 0·044). After adjusting for confounders, the associations of TSH and hair cortisol with pMDD were no longer significant. Furthermore, TSH and FT4 were not associated with PSS scores and hair cortisol levels. Summarising, iodine nutrition was adequate for adolescents with and without pMDD. However, FT4 concentrations were lower in those with pMDD, and 1 in 5 female adolescents with pMDD were hypothyroxinaemic.

Folic acid (FA) and iodine supplements are recommended by the Ministry of Health (MOH) for pregnant and/or lactating women in New Zealand (NZ)(1). Evidence suggests that many NZ women are not just taking FA and iodine in the form of a single-nutrient supplement (SNS) but are taking FA and iodine as part of a multivitamin supplement (MVS) which may or may not contain the recommended doses, and some are using a combination of both(2). No NZ study has examined the daily dose taken from both SNS and MVS for both FA and iodine across all time periods (2, 3). The aim of this study was to investigate what nutritional supplements containing FA and iodine were taken by postpartum NZ women, preconception, during the three trimesters of pregnancy and post-partum, and examine how well the women’s supplement use aligned with the NZ MOH recommendations. This cross-sectional observational study utilised data gathered on FA and iodine supplement use from an anonymous survey between February and August 2022. Descriptive statistics including frequency and percentages were reported. Folic acid and iodine weekly intakes from SNS and MVS were calculated by multiplying the amount of nutrient in each supplement, with the number of times per day taken, and the average number of days taken per week reported. A total of 584 women were included in the analysis. In addition to the SNS for FA (0.8mg and 5mg) and iodine (150 ug), women took 28 different MVS. Fifty-eight percent (preconception; 30% from SNS, 18% from MVS, and 10% from both) and 96% (1st trimester pregnancy; 61% from SNS, 17% from MVS, and 19% from both) of women took FA containing supplements. More than 75% of women reported taking iodine containing supplements during pregnancy (1st and 2nd trimesters: 93%, 3rd trimester: 89%) and postpartum (76%).Approximately 60% took SNS, 18% took only MVS and 14% took both. Based on the MOH recommendations, only 30% (preconception) and 62% (1st trimester) achieved sufficiency of FA supplementation at 0.8mg/day; 35% (preconception) and 69% (1st trimester) achieved sufficiency of FA at 5mg/day; around 50% women achieved sufficiency of iodine supplementation at 150 µg/day during pregnancy while only 37% during postpartum. The balance either took none, an insufficient dose or a dose that exceeded the recommended dose and many took them during non-recommended periods (FA after the 1st trimester; iodine preconception). Most women reported taking FA and/or iodine containing supplements at some point before, during and after their pregnancy. However, it is concerning that a large number of women do not seem to be adhering to the MOH recommendations for FA and iodine supplementation.

Mollusc and crustacean consumption in the first 1000 d may improve maternal and child health by providing essential nutrients. However, in some contexts, molluscs and crustaceans have been associated with allergies and environmental contamination, potentially leading to adverse health and development outcomes. It is unclear whether the health benefits of consuming molluscs and crustaceans, collectively classified as shellfish in nutrition, are outweighed by the potential risks to pregnant women and children. We conducted a scoping review (PROSPERO: CRD42022320454) in PubMed, Scopus and EBSCO Global Health of articles published between January 2000 and March 2022 that assessed shellfish consumption during pregnancy, lactation or childhood (0–2 years) in relation to maternal health, child health or child development. A total of forty-six articles were included in this review. Overall, shellfish consumption was associated with higher biomarkers of environmental contaminants, with mercury being the most studied and having the strongest evidence base. The limited research on nutritional biomarker status shows an association between shellfish consumption and iodine status. Preterm birth was not associated with shellfish consumption, but newborn anthropometry showed mixed results, with several studies reporting lower birth weight with higher shellfish consumption. The few studies that examined child development and maternal health outcomes reported no significant associations. This review revealed trade-off health risks and benefits with inclusion of molluscs and crustaceans in the dietary patterns of mothers and young children. More research is needed to understand how these aquatic animal-source foods may be safely consumed and leveraged for improving human nutrition.

Iodine is a trace element required to produce the thyroid hormones, which are critical for development, growth and metabolism. To ensure appropriate population iodine nutrition, convenient and accurate methods of monitoring are necessary. Current methods for determining iodine status either involve a significant participant burden or are subject to considerable intra-individual variation. The continuous secretion of iodide in saliva potentially permits its use as a convenient, non-invasive assessment of status in populations. To assess its likely effectiveness, we reviewed studies analysing the association between salivary iodide concentration (SIC) and dietary iodine intake, urinary iodide concentration (UIC) and/or 24-h urinary iodide excretion (UIE). Eight studies conducted in different countries met the inclusion criteria, including data for 921 subjects: 702 healthy participants and 219 with health conditions. SIC correlated positively with UIC and/or UIE in four studies, with the strength of relationship ranging from r = 0·19 to r = 0·90 depending on sampling protocol, age, and if salivary values were corrected for protein concentration. Additionally, SIC positively correlated with dietary intake, being strongest when saliva was collected after dinner. SIC varied with external factors, including thyroid function, use of some medications, smoking and overall health status. Evidence provided here supports the use of SIC as a viable, low-burden method for determining iodine status in populations. However, small sample sizes and high variability indicates the need for more extensive analyses across age groups, ethnicities, disease states and dietary groups to clarify the relative accuracy and reliability in each case and standardise procedure.

Iodine and thyroid hormones (TH) transport in the placenta are essential for fetal growth and development, but there is little research focus on the human placenta. The research aimed to investigate iodine and TH transport mechanisms in the human placenta. The placenta was collected from sixty healthy pregnant women. Urinary iodine concentration (UIC), serum iodine concentration (SIC), placenta iodine storage (PIS) and the concentration of serum and placenta TH were examined. Five pregnant women were selected as insufficient intake (II), adequate intake (AI) and above requirements intake (ARI) groups. Localisation/expression of placental sodium/iodide symporter (NIS) and Pendrin were also studied. Results showed that PIS positively correlated with the UIC (R = 0·58, P < 0·001) and SIC (R = 0·55, P < 0·001), and PIS was higher in the ARI group than that in the AI group (P = 0·017). NIS in the ARI group was higher than that in the AI group on the maternal side of the placenta (P < 0·05). NIS in the II group was higher than that in the AI group on the fetal side (P < 0·05). In the II group, NIS on the fetal side was higher than on the maternal side (P < 0·05). Pendrin was higher in the II group than in the AI group on the maternal side (P < 0·05). Free triiodothyronine (r = 0·44, P = 0·0067) and thyroid-stimulating hormone (r = 0·75, P < 0·001) between maternal and fetal side is positively correlated. This study suggests that maternal iodine intake changes the expression of NIS and Pendrin, thereby affecting PIS. Serum TH levels were not correlated with placental TH levels.

Self-diffusion coefficients of H2O molecules in water-rich gels of Na-rich expandable mica synthesized using natural talc were measured by pulsed-gradient spin-echo 1H nuclear magnetic resonance (NMR), and the dependence on mica fraction (0.00–43.8 wt.%) and temperature (30.0–60.9°C) was examined. On the basis of the NMR results, the self-diffusion coefficient of H2O, Dwater, in the gel can be expressed by ln(Dwater/D0water) = 1.64[exp( −0.0588w) - 1], where D0water is the self-diffusivity of bulk water at temperature and w is the weight fraction of the mica (wt.%). The activation energy of H2O diffusivity in mica gel is nearly equal to that in bulk water. These findings indicate that the normalized diffusivity, Dwater/D0water, is independent of temperature. The diffusivity of I−, Diodine, in the gels was examined by X-ray computed tomography (CT) at 22°C, and the influence of the mica fraction (0.00–24.8 wt.%) was studied to determine the contribution of bound H2O. The X-ray CT results show that the normalized I− diffusivity, Diodine/D0iodine, obeys the above-mentioned phenomenological curve where D0iodine is the I− diffusivity in bulk water. I− is non-sorbing, and thus its diffusion is restricted only by the geometrical complexity of the pore structure of gels. Therefore, the effect of bound H2O molecules on average H2O diffusivity is negligible for w <24.8 wt.%. Diffusivity is governed by free or unbound H2O molecules diffusing in the geometrically complex and tortuous pore structure of mica-mineral grains. This is a result of the large population of unbound H2O far from the grain surface compared to the small population of bound H2O near the grain surface. The diffusion of I− ions in montmorillonite gels was examined by X-ray CT for w <16.7 wt.% montmorillonite. The normalized iodine diffusivity, (Diodine/D0iodine) obtained is in reasonably close agreement with the literature data for the normalized diffusivity of H2O and is similar to the master curve of expandable mica. Therefore, bound H2O molecules near negatively charged clay surfaces do not play a major role in the H2O diffusivity for water-rich montmorillonite gels.

Plant-based substitutes (PBS) are seen as a convenient way to transition to a more plant-based diet, but their potential health benefits and nutritional concerns remain debated. Based on a review of the literature, it is concluded here that the primary risk of insufficient nutrient intake with PBS concerns iron and calcium, which are critical to the nutritional value of PBS. Other risks were identified but these would depend on the characteristics of the overall diet, as is the case for iodine in a diet containing no seafood or dairy, and vitamin B12 in a vegetarian/vegan diet. Conversely, the use of PBS is also expected to confer some benefits for long-term health because it would result in higher fibre intakes (in the case of meat PBS) and lower SFA intakes (but higher PUFA/MUFA intakes), but attention should be paid to a potential increase in sodium intake with PBS of meat products. In fact, a recurring finding in this review was that PBS is a very heterogeneous food category involving considerable variations in ingredient and nutrient composition, and whose design could be improved in order to foster nutritional and health benefits. The latter also depend on the animal food that is being replaced and are only deemed likely when PBS replace red meat. The fortification of PBS with key nutrients such as iron and calcium may constitute an actionable public health solution to further shift the balance in favour of PBS in the context of the current dietary transition in western countries.

An increasing number of food-based recommendations promote a plant-based diet to address health concerns and environmental sustainability in global food systems. As the main sources of iodine in many countries are fish, eggs and dairy products, it is unclear whether plant-based diets, such as the EAT-Lancet reference diet, would provide sufficient iodine. This is important as iodine, through the thyroid hormones, is required for growth and brain development; adequate iodine intake is especially important before, and during, pregnancy. In this narrative review, we evaluated the current literature and estimated iodine provision from the EAT-Lancet reference diet. There is evidence that those following a strict plant-based diet, such as vegans, cannot reach the recommended iodine intake from food alone and are reliant on iodine supplements. Using the EAT-Lancet reference diet intake recommendations in combination with iodine values from UK food tables, we calculated that the diet would provide 128 μg/d (85 % of the adult recommendation of 150 μg/d and 51–64 % of the pregnancy recommendation of 200–250 μg/d). However, if milk is replaced with unfortified plant-based alternatives, total iodine provision would be just 54 μg/d (34 % and 22–27 % of the recommendations for adults and pregnancy, respectively). Plant-based dietary recommendations might place consumers at risk of iodine deficiency in countries without a fortification programme and where animal products provide the majority of iodine intake, such as the UK and Norway. It is essential that those following a predominantly plant-based diet are given appropriate dietary advice to ensure adequate iodine intake.

Mild-to-moderate iodine deficiency remains a problem worldwide, including in Norway. Of particular, concern is fertile, pregnant and lactating women. The Norwegian Dairy Council developed a digital iodine-specific dietary screener (I-screener) for the assessment of iodine intake levels but has yet to be validated. The aim was thus to investigate the relative validity of the I-screener by comparing estimates of iodine intake from the I-screener against a single 24-hour recall (24HR) and urinary iodine concentration (UIC) in fertile women. Healthy females were recruited in Bergen in August–December 2021. Six spot-urine samples from six consecutive days were collected into a pooled sample to assess UIC. Each participant completed a single administration of the I-screener and the 24HR. The estimated daily iodine intake from the I-screener was compared with the estimations from the 24HR and UIC. Seventy-two women aged 19–39 completed the study. The median UIC was 76 μg/l. Compared with the 24HR, the I-screener placed 83 % of the participants in the same/adjacent tertial, with a slight agreement between the methods (Cohen's kappa = 0⋅187). The present study shows an acceptable correlation between the I-screener and the 24HR (r = 0⋅318), but not between the I-screener and UIC (r = 0⋅122). Despite its varying iodine estimate abilities, the I-screener may be used as an initial screening tool to rank fertile women on an individual level into deficient inadequate, and sufficient iodine intake. However, due to the relatively high risk of misclassification, further assessment of iodine status should follow.

Iodine is an essential nutrient that may change the occurrence of autoimmune thyroiditis (AIT). Apoptosis and DNA methylation participate in the pathogenesis and destructive mechanism of AIT. We detected the methylation and the expression of mRNA of intrinsic apoptosis-associated genes (YWHAG, ING4, BRSK2 and GJA1) to identify the potential interactions between the levels of methylation in these genes and different levels of iodine. 176 adult patients with AIT in Shandong Province, China, were included. The MethylTargetTM assay was used to verify the levels of methylation. We used PCR to detect the mRNA levels of the candidate genes. Interactions between methylation levels of the candidate genes and iodine levels were evaluated with multiplicative and addictive interaction models and GMDR. In the AIT group, YWHAG_1 and six CpG sites and BRSK2_1 and eight CpG sites were hypermethylated, whereas ING4_1 and one CpG site were hypomethylated. A negative correlation was found between methylation levels of YWHAG and mRNA expression. The combination of iodine fortification, YWHAG_1 hypermethylation and BRSK2_1 hypermethylation was significantly associated with elevated AIT risk. A four-locus model (YWHAG_1 × ING4_1 × BRSK2_1 × iodine level) was found to be the best model of the gene–environment interactions. We identified abnormal changes in the methylation status of YWHAG, ING4 and BRSK2 in patients with AIT in different iodine levels. Iodine fortification not only affected the methylation levels of YWHAG and BRSK2 but also interacted with the methylation levels of these genes and may ultimately increase the risk of AIT.

Vegan and vegetarian diets are widely supported and adopted, but individuals following such diets remain at greater risk of iodine deficiency. This systematic review and meta-analysis was conducted to assess the iodine intake and status in adults following a vegan or vegetarian diet in the modern day. A systematic review and quality assessment were conducted from October 2020 to December 2022 according to Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) and Meta-analysis of Observational Studies in Epidemiology (MOOSE) guidance. Studies were identified in Ovid MEDLINE, Web of Science, PubMed, and Scopus. Eleven articles were eligible for review containing 4421 adults (aged ≥ 18 years). Vegan groups had the lowest median urinary iodine concentration (mUIC) (12·2/l). None of the dietary groups had mUIC within the optimal range for iodine status (100–200 µg/l) (WHO). Vegan diets had the poorest iodine intake (17·3 µg/d) and were strongly associated with lower iodine intake (P = < 0·001) compared with omnivorous diets. Lower intake in vegan diets was influenced by sex (P = 0·007), the presence of voluntary or absence of Universal Salt Iodisation (USI) programmes (P = 0·01 & P = < 0·001), and living in a country with adequate iodine nutrition (P = < 0·001). Vegetarians and particularly vegans living in countries with no current USI programme continue to have increased risk of low iodine status, iodine deficiency and inadequate iodine intake. Further research into the usefulness of mandatory fortification of vegan appropriate foods is required.

Iodine deficiency may cause thyroid dysfunction. The iodine intake in a population is measured by urinary iodine concentration (UIC) in spot samples or 24-h urinary iodine excretion (24UIE). 24UIE is considered the gold standard and may be estimated using an equation including UIC, urinary creatinine concentration, sex and age (e24UIE). The aims of this study were to evaluate the preferable timing of UIC when using this equation and assess the variability of UIE. Sixty healthy non-smoking women (n 31) and men (n 29) were included in Gothenburg, Sweden. Twelve urine samples were collected at six fixed times on two separate days. Variability was calculated for UIC, 24UIE, e24UIE, iodine excretion per hour (iHr) and UIC adjusted for creatinine and specific gravity. Median 24UIE was 156 µg/24 h and the median UIC (all spot samples) was 104 µg/l. UIC (P < 0·001), 24UIE (P = 0·001) and e24UIE (P < 0·001) were significantly higher in men. e24UIE was relatively similar to 24UIE. However, when e24UIE was calculated from UIC in the first void, it was about 15 % lower than 24UIE (P < 0·001). iHr was lowest in the morning and highest in the afternoon. Median iHr was higher in men (7·4 v. 5·3 µg/h, P < 0·001). The variability of UIE was higher within individuals than between individuals. This study suggests that most time points for estimation of individual 24UIE are appropriate, but they should preferably not be collected in the first void.

Iodine is required for thyroid hormone synthesis and fetal neurogenesis. Recent population studies in the United Kingdom (UK) have found iodine deficiency among schoolgirls, women of child-bearing age and pregnant women. This review explores knowledge and awareness of iodine among women of child-bearing age and healthcare professionals (HCPs) in the UK, set within a global context. We aimed to identify gaps in iodine knowledge in the current UK setting of iodine deficiency without iodine fortification and where iodine is not included in antenatal guidelines. The search terms ‘iodine knowledge’ and ‘iodine awareness’ were used to identify relevant papers. Iodine knowledge is poor among women of child-bearing age in the UK according to four studies using questionnaires and qualitative methods. They were unsure of dietary sources of iodine and were not consistently provided with relevant information from HCPs during clinical care. Midwives have been recognised as the main providers of dietary information during pregnancy and, although they recognised the importance of their role in providing nutrition advice, they did not feel equipped to do so and lacked confidence in addressing nutritional concerns. Globally, there was a similar lack of knowledge, however, this was somewhat improved by the inclusion of iodine in antenatal care guidelines. Midwives’ knowledge of iodine was poor, as was knowledge among women of child-bearing age. Improved HCP knowledge and effective communication of information to pregnant women and women planning to conceive may help to improve iodine status which is of particular concern in pregnancy.

Iodine, through the thyroid hormones, is required for the development of the auditory cortex and cochlea (the sensory organ for hearing). Deafness is a well-documented feature of endemic cretinism resulting from severe iodine deficiency. However, the range of effects of suboptimal iodine intake during auditory development on the hearing ability of children is less clear. We therefore aimed to systematically review the evidence for the association between iodine exposure (i.e. intake/status/supplementation) during development (i.e. pregnancy and/or childhood) and hearing outcomes in children. We searched PubMed and Embase and identified 330 studies, of which thirteen were included in this review. Only three of the thirteen studies were of low risk of bias or of good quality, this therefore limited our ability to draw firm conclusions. Nine of the studies (69 %) were in children (one RCT, two non-RCT interventions and six cross-sectional studies) and four (31 %) were in pregnant women (one RCT, one cohort study and two case reports). The RCT of iodine supplementation in mildly iodine-deficient pregnant women found no effect on offspring hearing thresholds. However, hearing was a secondary outcome of the trial and not all women were from an iodine-deficient area. Iodine supplementation of severely iodine-deficient children (in both non-RCT interventions) resulted in improved hearing thresholds. Five of six cross-sectional studies (83 %) found that higher iodine status in children was associated with better hearing. The current evidence base for the association between iodine status and hearing outcomes is limited and further good-quality research on this topic is needed.