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Iodine Deficiency in Pregnant Women

A recent study published in the British Journal of Nutrition highlights the importance of iodine in pregnancy and adds to evidence that British women are increasingly being found to be iodine deficient.

Iodine, as a component of the thyroid hormones, is required for brain development, particularly in the fetus, therefore an adequate intake of iodine is very important during pregnancy. While extreme iodine deficiency in pregnancy can result in cretinism, even mild-to-moderate iodine deficiency in UK pregnant women has been associated with reduced cognitive scores in their children (Bath et al., 2013). The World Health Organisation (WHO) iodine requirement for pregnant women is nearly double that of non-pregnant adults (250 vs. 150 μg/day).

Based on a national survey of schoolgirls in 2009, the UK is now classified as mildly iodine deficient by the WHO (Vanderpump et al., 2011). Despite the importance of adequate iodine intake during pregnancy, there are relatively few studies of iodine status in UK pregnant women, and no data have been collected on iodine status in pregnant women living in the South East of the UK.

Researchers at The University of Surrey recruited 100 pregnant women at 12 weeks gestation from the Royal Surrey County Hospital. Women provided a spot-urine sample for the measurement of iodine status; urinary iodine excretion is considered to be a good biomarker of iodine status and is used to estimate status in a population. 24-hr iodine excretion was then estimated using urinary creatinine concentration to explore relationships between iodine status and dietary intake. The women also completed a short food-frequency questionnaire that collected data on intake of iodine-rich foods.

According to WHO criteria, the women were classified as mildly-to-moderately iodine deficient; the median urinary iodine concentration, at 85.3 μg/L, is considerably below the WHO cut-off for adequacy of 150 μg/L. Furthermore, the estimated 24-hr iodine excretion value was much lower than would have been expected if women had been meeting the WHO requirement of 250 μg/day. The authors pointed out that this, together with studies showing iodine deficiency in pregnant women in other regions of the UK, raises concern for the brain development of UK babies.

Of the dietary sources investigated, intake of milk was the strongest predictor of maternal iodine status, echoing results from other studies that show milk is the major source of iodine in the UK diet. Women who reported taking a prenatal supplement containing iodine (42%) had a significantly higher iodine status than women who did not use such a supplement.

It is important to note that not all prenatal supplements in the UK contain iodine – check to make sure that the one you are using includes iodine to make up for your increased requirements during pregnancy.

Bath S C, Walter A, Taylor A, Wright J, Rayman M P (2014) Iodine deficiency in pregnant women living in the South East of the UK: the influence of diet and nutritional supplements on iodine status. British Journal of Nutrition, doi:10.1017/S0007114513004030

Bath S C, Steer C D, Golding J, et al. (2013) Effect of inadequate iodine status in UK pregnant women on cognitive outcomes in their children: results from the Avon Longitudinal Study of Parents and Children (ALSPAC). Lancet 382, 331–337.

Vanderpump M P, Lazarus J H, Smyth P P, et al. (2011) Iodine status of UK schoolgirls: a cross-sectional survey. Lancet 377, 2007–2012

Categories: Nutritional News, Children's Health