Endocrine Abstracts

Iodine is an essential component of thyroid hormones that are required for brain development. Severe iodine deficiency during pregnancy can result in cognitive impairment and lower IQ in the offspring. However, the effects of mild-to-moderate iodine deficiency on brain development and neurocognitive function are less well known, and this is important as mild-to-moderate deficiency is common in pregnancy in many European countries, including the UK. There are recommendations in some countries with mild-to-moderate iodine deficiency for pregnant women, lactating women, and those planning a pregnancy to take an iodine supplement. However, the evidence on which these recommendations are based is not strong. There are three non-randomised intervention studies with cognitive outcomes, two suggest a benefit of iodine supplementation but all have limitations that mean interpretation is difficult. Observational studies have found mixed results, with some studies even suggesting a negative effect on child neurodevelopment, either when the dose of iodine was relatively high (>150 μg/day) or when iodine supplements were started during, rather than prior to, pregnancy. However, given their observational nature, these studies need to be interpreted with caution. There is a lack of evidence from randomised controlled trials (RCTs) in pregnancy; though a recent RCT in India and Thailand found no benefit of iodine supplementation on child cognition, the women recruited were only marginally iodine deficient. Thus further evidence from RCTs in pregnant women from regions of moderate iodine deficiency is required to strengthen the evidence base for public-health recommendations. However, it may become increasingly challenging to conduct such a trial, because it may be considered unethical to include a placebo group, especially in countries with official recommendations for iodine supplementation in pregnancy.