To the Editor: I refer to the article by Gallego and colleagues in the 19 April 2010 issue of the Journal,1 which stated that (as at the time of writing, in July 2009) Australia had no formal policies for iodine supplementation in pregnant and lactating women. In January 2010, the National Health and Medical Research Council (NHMRC) released a public statement, Iodine supplementation for pregnant and breastfeeding women.2

The NHMRC recommends that women who are pregnant, breastfeeding or considering pregnancy take an iodine supplement of 150 μg each day; and women with pre-existing thyroid conditions should seek advice from their medical practitioner before taking a supplement. The public statement also provides information on the increased need for iodine during pre-pregnancy, pregnancy and breastfeeding, the risks of not having enough iodine and the types of supplement that should and should not be used.

The statement was developed in consultation with an expert reference group and was based on a review of recent international scientific literature for the efficacy of iodine supplementation in increasing iodine levels in pregnant and breastfeeding women to levels that mitigate the risks associated with iodine deficiency.3

The public statement and supporting literature review can be found on the NHMRC website.2,3

To the Editor: We disagree with the opinion expressed by Gallego and colleagues that Australian “women planning a pregnancy and pregnant and lactating women should be advised to take an iodine supplement”,1 and offer two reasons to support our view.

First, the data suggesting mild iodine deficiency in Australian women were collected from opportunistic samples of women not representative of the population at large and were obtained before the introduction of mandatory iodine fortification of bread in October 2009. We believe that recommending iodine supplementation in pregnancy without evaluating the effect of mandatory iodine fortification on iodine intake and status of pregnant women in Australia is premature.2 This is supported by a recent report, developed by the Dietitians Association of Australia on behalf of the National Health and Medical Research Council (NHMRC).3 The report clearly shows that the recommended iodine intake for pregnant women (recommended dietary allowance, 220 μg/day) is achievable from foods alone, together with iodine fortification of bread.

Second, there are no randomised controlled trials (RCTs) that have examined the effect of iodine supplementation of pregnant women from regions of mild iodine deficiency (as in Australia) on neurodevelopment of the offspring or any other clinical outcomes. Gallego et al state that “iodine-containing supplements consistently benefit the iodine and thyroid status of both mother and newborn”, citing a review of iodine supplementation of pregnant women from populations with mild-to-moderate iodine deficiency.4 In fact, none of the six RCTs included in that review showed a clear effect of supplementation on maternal and newborn thyroid hormone concentrations, which suggests that the maternal thyroid is able to adapt to meet the increased thyroid hormone requirements of pregnancy in areas of mild-to-moderate iodine deficiency.5 Furthermore, Gallego et al cite no evidence to support their statement “Even subclinical hypothyroidism in the mother, occurring as a consequence of iodine deficiency, can cause irreversible brain damage in the fetus . . .”.

In our view, major public health recommendations advising routine iodine supplementation for women planning a pregnancy, as well as pregnant and lactating women, should await the results of current RCTs6-8 examining the effect of maternal iodine supplementation on longer-term maternal health and neurodevelopmental outcome of children in regions with mild-to-moderate iodine deficiency, including Australia and New Zealand.

In reply: While Zhou and colleagues disagree with our viewpoint that Australian “women planning a pregnancy and pregnant and lactating women should be advised to take an iodine supplement”,1 we note that they suggest any such recommendation should await the results of their planned randomised controlled trial (RCT) examining the effects of maternal iodine supplementation on maternal health and neurodevelopmental outcome of the offspring. They neglect to mention that the National Health and Medical Research Council (NHMRC) issued a public statement in January this year, with supporting evidence attached, stating that: “The NHMRC recommends that all women who are pregnant, breastfeeding or considering pregnancy take an iodine supplement of 150 μg each day”.2 Similar recommendations, based upon available scientific evidence, have been issued by the World Health Organization, International Council for Control of Iodine Deficiency Disorders, American Thyroid Association and American Endocrine Society.

We agree that there is a paucity of RCT evidence examining the effect of iodine supplementation of pregnant women living in mildly iodine-deficient areas, and this is regrettable. Given the overwhelming animal and human evidence that maternal iodine deficiency causes brain damage in the offspring of deficient mothers, we consider there are major ethical issues in conducting such trials where pregnant women would be deprived of iodine and their babies put at risk of brain damage.

Zhou and colleagues imply that mild-to-moderate iodine deficiency is not widely prevalent in Australia. This statement ignores the evidence from several clinical studies of pregnant women in New South Wales, Victoria and Tasmania, all showing that mild-to-moderate iodine deficiency is widespread in the majority of the Australian population. Analysis of the data in some of these studies shows between 20% and 40% of women tested are moderately to severely iodine deficient.3 Furthermore, food modelling studies by Food Standards Australia New Zealand (FSANZ) predict between 45% and 75% of Australian women will continue to be iodine deficient after the mandatory use of iodised salt in bread that commenced in October 2009.4

Finally, we disagree with their assertion that the recommended iodine intake for pregnant women can be achieved by the majority of women from foods alone, together with iodine fortification of bread. A trial of bread fortification in Tasmania showed this was not achievable.5 If this were achievable, it is questionable why Zhou and colleagues would even consider conducting an RCT of maternal iodine supplementation in pregnant women in Australia and NZ.