Iodine status of pregnant women with obesity from inner city populations in the United Kingdom

Thyroid function and iodine intake: global recommendations and relevant dietary trends

Iodine is a micronutrient that is essential for thyroid hormone production. Adequate iodine intake is especially important during pregnancy and early life, when brain development is dependent on thyroid hormones. Iodine intake recommendations vary around the world, but most recommendations generally reflect the increased requirements during pregnancy and lactation, although adequate iodine intake before pregnancy is also important. Tremendous progress has been made in improving iodine intake across the world over the past 30 years, mainly through salt-iodization programmes. However, in countries without strong iodine fortification programmes, and with shifts in dietary patterns, a need has arisen for health organizations, governments and clinicians to ensure that adequate iodine is consumed by everyone in the population. For example, in countries in which adequate iodine intake depends on individual food choice, particularly of iodine-rich milk and dairy products, intake can be highly variable and is also vulnerable to changing dietary patterns. In this Review, iodine is considered in the wider context of the increasing prevalence of overweight and obesity, the dietary trends for salt restriction for cardiovascular health and the increasing uptake of plant-based diets.

Iodine and plant-based diets: a narrative review and calculation of iodine content

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.

Associations between urinary iodine concentration and the prevalence of metabolic disorders: a cross-sectional study

Background

Few studies have examined the role of iodine in extrathyroidal function. Recent research has shown an association between iodine and metabolic syndromes (MetS) in Chinese and Korean populations, but the link in the American participants remains unknown.

Purpose

This study aimed to examine the relationship between iodine status and metabolic disorders, including components associated with metabolic syndrome, hypertension, hyperglycemia, central obesity, triglyceride abnormalities, and low HDL.

Methods

The study included 11,545 adults aged ≥ 18 years from the US National Health and Nutrition Examination Survey (2007-2018). Participants were divided into four groups based on their iodine nutritional status(ug/L), as recommended by the World Health Organization: low UIC, < 100; normal UIC, 100-299; high UIC, 300-399; and very high, ≥ 400. The Odds ratio (OR) for MetS basing the UIC group was estimated using logistic regression models for our overall population and subgroups.

Results

Iodine status was positively associated with the prevalence of MetS in US adults. The risk of MetS was significantly higher in those with high UIC than in those with normal UIC [OR: 1.25; 95% confidence intervals (CI),1.016-1.539; p = 0.035). The risk of MetS was lower in the low UIC group (OR,0.82; 95% CI: 0.708-0.946; p = 0.007). There was a significant nonlinear trend between UIC and the risk of MetS, diabetes, and obesity in overall participants. Participants with high UIC had significantly increased TG elevation (OR, 1.24; 95% CI: 1.002-1.533; P = 0.048) and participants with very high UIC had significantly decreased risk of diabetes (OR, 0.83; 95% CI: 0.731-0.945, p = 0.005). Moreover, subgroup analysis revealed an interaction between UIC and MetS in participants aged < 60 years and ≥ 60 years, and no association between UIC and MetS in older participants aged ≥ 60 years.

Conclusion

Our study validated the relationship between UIC and MetS and their components in US adults. This association may provide further dietary control strategies for the management of patients with metabolic disorders.

Optimizing Growth: The Case for Iodine

Iodine is an essential micronutrient and component of thyroid hormone. An adequate dietary iodine intake is critical to maintain and promote normal growth and development, especially during vulnerable life stages such as pregnancy and early infancy. The role of iodine in cognitive development is supported by numerous interventional and observational studies, and when iodine intake is too low, somatic growth is also impaired. This can be clearly seen in cases of untreated congenital hypothyroidism related to severe iodine deficiency, which is characterized, in part, by a short stature. Nevertheless, the impact of a less severe iodine deficiency on growth, whether in utero or postnatal, is unclear. Robust studies examining the relationship between iodine and growth are rarely feasible, including the aspect of examining the effect of a single micronutrient on a process that is reliant on multiple nutrients for optimal success. Conversely, excessive iodine intake can affect thyroid function and the secretion of optimal thyroid hormone levels; however, whether this affects growth has not been examined. This narrative review outlines the mechanisms by which iodine contributes to the growth process from conception onwards, supported by evidence from human studies. It emphasizes the need for adequate iodine public health policies and their robust monitoring and surveillance, to ensure coverage for all population groups, particularly those at life stages vulnerable for growth. Finally, it summarizes the other micronutrients important to consider alongside iodine when seeking to assess the impact of iodine on somatic growth.

Maternal Iodine Status and Birth Outcomes: A Systematic Literature Review and Meta-Analysis

Background & aims: Iodine is important for thyroid function during pregnancy to support fetal growth, but studies of maternal iodine status and birth outcomes are conflicting. We aimed to quantify the association between iodine status and birth outcomes, including potential threshold effects using nonlinear dose−response curves. Methods: We systematically searched Medline and Embase to 10 October 2022 for relevant cohort studies. We conducted random-effects meta-analyses of urinary iodine concentration (UIC), iodine:creatinine ratio (I:Cr), and iodide intake for associations with birth weight, birth weight centile, small for gestational age (SGA), preterm delivery, and other birth outcomes. Study quality was assessed using the Newcastle-Ottawa scale. Results: Meta-analyses were conducted on 23 cohorts with 42269 participants. Birth weight was similar between UIC ≥ 150 μg/L and <150 μg/L (difference = 30 g, 95% CI −22 to 83, p = 0.3, n = 13, I2 = 89%) with no evidence of linear trend (4 g per 50 μg/L, −3 to 10, p = 0.2, n = 12, I2 = 80%). I:Cr was similar, but with nonlinear trend suggesting I:Cr up to 200 μg/g associated with increasing birthweight (p = 0.02, n = 5). Birthweight was 2.0 centiles (0.3 to 3.7, p = 0.02, n = 4, I2 = 0%) higher with UIC ≥ 150 μg/g, but not for I:Cr. UIC ≥ 150 μg/L was associated with lower risk of SGA (RR = 0.85, 0.75 to 0.96, p = 0.01, n = 13, I2 = 0%), but not with I:Cr. Conclusions: The main risk of bias was adjustment for confounding, with variation in urine sample collection and exposure definition. There were modest-sized associations between some measures of iodine status, birth weight, birth weight centile, and SGA. In pregnancy, we recommend that future studies report standardised measures of birth weight that take account of gestational age, such as birth weight centile and SGA. Whilst associations were modest-sized, we recommend maintaining iodine sufficiency in the population, especially for women of childbearing age on restricted diets low in iodide.

Iodine status in pregnant women and infants in Finland

PURPOSE

Iodine insufficiency during pregnancy may adversely influence fetal growth and development. There is a lack of information on iodine status in pregnant women and infants in many countries including Finland. The aim of this study is to determine dietary intake of iodine and the iodine status in a population of Finnish pregnant women and their infants.

METHODS

Urine samples were collected from women participating in a mother-child clinical study at early (n = 174) and late pregnancy (n = 186) and at three months of postpartum (n = 197), when infant samples were also collected (n = 123). Urine iodine concentration was measured using inductively coupled plasma mass spectrometry. Cutoffs for iodine insufficiency were < 150 µg/L during pregnancy and < 100 µg/L at postpartum and in infants. Iodine intake was assessed using 3-day food diaries.

RESULTS

Increased risk of insufficiency, based on urinary iodine concentrations, was observed in the groups investigated in this study. Of the women studied, 66% had urinary iodine concentrations indicating insufficient intakes and iodine insufficiency at early pregnancy, 70% at late pregnancy and 59% at three months of postpartum. This was also the case in 29% of the three-month-old infants. Estimation of iodine intake revealed that iodine insufficient women had lower intakes of iodine from the diet, from food supplements and from diet plus supplements than iodine sufficient women in early pregnancy and at three months of post-partum. In late pregnancy, this difference was seen for iodine intake from supplements.

CONCLUSION

The majority of the women manifested with low urine iodine concentrations both during and after pregnancy. Similarly, one-third of the infants presented with iodine insufficiency. Maternal iodine intake data support these findings. These observations may have implications for optimal child cognitive development.

Nutritional iodine status and obesity

Iodine is an essential component of the thyroid hormones, thyroxine and triiodothyronine. Its availability strictly depends on iodine content of foods, which may vary from very low to very high. Inadequate iodine intake (deficiency or excess) may affect thyroid function resulting in hypothyroidism or hyperthyroidism. Based on median urinary iodine concentrations, epidemiological criteria have been established for the categorization and monitoring of nutritional iodine status of a population (or subgroups of populations). Additional methods for iodine intake assessment include measurement of thyroid size (by thyroid palpation or ultrasonography) and of biochemical parameters, such as neonatal thyroid stimulating hormone, thyroglobulin and thyroid hormones.

Recent studies carried out in overweight/obese children and adults provide evidence that body mass index (BMI) may significantly influence the above indicators, thus theoretically affecting the epidemiological evaluation of nutritional iodine status in populations.

In this short review, we analyze current knowledge on the effects of overweight and obesity on indicators of adequacy and monitoring of iodine status, namely urinary iodine excretion and thyroid volume and echogenicity.

Data on urinary iodine excretion in overweight/obese children are divergent, as both increased and reduced levels have been reported in overweight/obese children compared to normal-weight controls.

Whether gastrointestinal surgery may affect iodine absorption and lead to iodine deficiency in patients undergoing bariatric surgery has been evaluated in a limited number of studies, which excluded iodine deficiency, thus suggesting that supplements usually recommended after bariatric surgery do not need to include iodine.

Albeit limited, evidence on thyroid volume and obesity is consistent with a direct relationship between thyroid volume and BMI, irrespective of nutritional iodine status. Finally, a higher frequency of thyroid hypoechoic pattern has been described in overweight/obese children. This finding has been recently related to an increased adipocyte infiltration and thyroid parenchyma imbibition mediated by inflammatory cytokines and should be considered when the frequency of thyroid hypoechoic pattern is used as non-invasive marker to indirectly assess thyroid autoimmunity in monitoring Universal Salt Iodization programs. Further studies, specifically addressing the role of schoolchildren body mass index as a factor potentially influencing iodine intake indicators are needed.

Community Pharmacist-Led Interventions to Improve Preconception and Pregnancy Health: A Systematic Review

Background: Community pharmacist-led interventions are effective in improving health outcomes; however, their impact in improving preconception and pregnancy health is not clear. This study evaluated the effectiveness of community pharmacist-led interventions which aimed to improve health outcomes of preconception and pregnant women. Methods: A systematic review of the literature, consistent with PRISMA guidelines, was performed. Five electronic databases were searched up to February 2021. Results: Four studies, three in pregnant women and one in preconception women, were identified. The studies focused on improving micronutrient status and smoking cessation. The studies increased knowledge about, and use of, iron supplements, and improved iron status and smoking cessation rates in pregnant women, while improving knowledge regarding, and increasing the use of, preconception folic acid. The studies were ranked as weak to moderate quality. Conclusion: This review provides preliminary evidence for the potential benefit of community pharmacist-led interventions to improve the health of women before and during pregnancy.