Assessing iodine intakes in pregnancy: why does this matter?

The study by Condo et al. in this issue of the British Journal of Nutrition assessed the utility of a forty-four-item FFQ for use in determining the iodine intake of pregnant Australian women. This is the first such study designed specifically for pregnancy. A strength of the study was the administration of the FFQ at two different time points in gestation, which allowed for assessment of the reproducibility of results. The study validated the FFQ against multiple standards, including spot and 24 h urinary iodine concentrations, measurements of serum thyroglobulin and thyroid function tests (although thyroid function tends to be poorly correlated with iodine intake), and 4-d weighed food records. Why is the accurate ascertainment of iodine intake in pregnant women important? First, pregnant women and their fetuses are particularly vulnerable to the effects of iodine deficiency disorders. Adequate maternal iodine intake is essential for normal fetal neurodevelopment. Worldwide, iodine deficiency remains the leading preventable cause of intellectual impairments. Severe iodine deficiency is associated with an increased risk for stillbirth, miscarriage, congenital anomalies and perinatal mortality. Even mild iodine deficiency has recently been linked to lowered intelligence quotient and school performance. Second, both iodine requirements and typical diets are different in pregnant compared with non-pregnant adults. Pregnant women need increased iodine intake due to increased thyroid hormone production, increased renal losses and transfer of iodine to the fetus. In non-pregnant adults, the recommended daily iodine intake is 150mg. In Australia and New Zealand, the reference dietary intake for iodine in pregnancy is 220mg/d, similar to the 220mg/d RDA set by the US Institute of Medicine, and the 250mg daily intake recommended by the WHO. By contrast, the UK fails to recommend increased iodine intake in pregnancy, defining the reference nutrient intake as only 140mg/d during gestation. Assessing the iodine status of individuals is challenging due to the lack of an individual biomarker. Although median urinary iodine concentrations can be used to assess the iodine status of populations, the marked day-to-day variability in typical iodine excretion means that ten urine samples are needed in order to estimate an individual’s iodine status with reasonable precision. Blood thyroglobulin measurements have been established as an index of population iodine status in schoolaged children, but not in pregnant women. Iodine is found in a wide variety of foods; however, in many regions, iodine content in food is both highly variable and unlabelled. Data from a well-validated FFQ could complement the use of biomarkers for population studies in pregnancy. A FFQ on iodine intake could also potentially inform recommendations for individual patients, although, given the many competing demands on provider time, a forty-four-item questionnaire may be impractical for use in the clinical setting. Assessing iodine intake in pregnancy is currently of particular importance in Australia. Although historically iodine deficiency was recorded in Australia, by the 1980s, Australia appeared to be iodine sufficient, probably as a result of the use of iodophor cleansers by the dairy industry. Since the 1980s, the use of iodophors in the dairy industry has declined. Several studies performed in the last 15 years demonstrated mild-to-moderate iodine deficiency among pregnant women in different regions of Australia. In response to these data, starting in October 2009, the use of iodised salt was mandated in Australia and New Zealand for making all breads except organic bread. Due to concerns that this approach might not be adequate to meet the increased iodine requirements of pregnancy, starting in 2010, the National Health and Medical Research Council recommended that all Australian women who are pregnant, breast-feeding or considering pregnancy should take a daily supplement of 150mg of iodine. The data from Condo et al. suggest that this recommendation has not been universally adopted; only 75 % of the pregnant women in their study have reported the use of iodine-containing supplements. This is consistent with recent surveys demonstrating poor knowledge about the importance of iodine in pregnancy among both pregnant women and their health care providers. Reassuringly, the median spot urinary iodine concentration in the study by Condo et al. was 212mg/l, consistent with iodine sufficiency by WHO criteria. Urinary iodine concentrations were significantly lower in the twenty-four women who did not report ingesting iodine-containing supplements. Another recent Australian study has similarly demonstrated iodine sufficiency among only those pregnant women who were ingesting iodine-containing supplements. FFQ along with urinary iodine measurements could be utilised to gain a better understanding of both current iodine status and iodine sources among pregnant and lactating Australian women. British Journal of Nutrition (2015), 113, 1179–1181 q The Author 2015