In his presentation, Prof. Delange critically reviewed the scientific data on iodine requirements during pregnancy, lactation and the neonatal period 1 . In addition, he summarised the current worldwide experience of using measurements of the concentration of thyroid stimulating hormone (TSH) in blood from neonates as a tool to evaluate and control iodine deficiency disorders 1 . My response addresses these two main topics. Iodine requirements during pregnancy, lactation and the neonatal period

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... Table 1 compares the current WHO recommended nutrient intake (RNI) of iodine during pregnancy, lactation and the neonatal period 2 , and Prof. Delange's proposed new iodine intakes. Since no change is proposed in the RNI for neonates, I will not address this group. There are two main ways to judge the intake of iodine by pregnant and lactating women: measuring the excretion of iodine in urine, and by estimating physiological needs. Estimating the RNI from data on urinary iodine excretion As Prof. Delange points out, the data in Table 1 of his paper 1 reveal a wide range of iodine intakes by pregnant women (as estimated by the urinary iodine concentration) both in countries where the population is deemed to be iodine sufficient (145 -786 mg day 21 ) and in populations of iodine deficient countries (24-255 mg day 21 ). It is interesting that where comparisons can be made, the average iodine intake of pregnant women is greater by approximately 35 -45 mg day 21 compared with the general population. This may be because a proportion of these women take iodine in a prenatal micronutrient supplement during their pregnancy. However, I agree that these ranges are too wide to allow any conclusions to be made about the RNI during pregnancy. An examination of the data Delange presents in Table 2 1 leads to the same conclusion regarding lactation. Estimates of the RNI based on physiology Several studies have confirmed an increase in maternal thyroxine production during pregnancy, which necessitates an increase in maternal iodine intake 3 . The increased production of thyroxine results from several factors including: oestrogen stimulation of thyroxine binding globulin (TBG) leading to an increase in the reservoir of maternal thyroxine (T 4 ); the transfer of thyroxine to the foetus; and the activity of 5-deiodinase III in the placenta, which is likely to result in the transfer of iodine to the foetus. A study has shown that athyreotic women need on average a 50% increase in their dose of levothyroxine (l-T 4 ) during pregnancy 4 . This study also provided evidence of a 50 -75 mg day 21 increase in l-T 4 production, equivalent to a need for an extra 30-50 mg day 21 of iodine by a pregnant woman. In a similar manner, there is an increase in the maternal iodine requirement during lactation. Using a breast milk iodine content of 150-180 mg l 21 and an estimated daily consumption of 0.5 l of milk by a neonate and 1.5 l by an infant, a lactating mother would need an increase of approximately 0.5 l £ 150 mg l 21 ¼ 75 mg day 21 for a neonate and 1.5 l £ 150 mg l 21 ¼ 225 mg day 21 for an infant. If one adds these figures to the RNI for an adult of 150 mg day 21 recommended by the WHO, a lactating woman would need a total of 225-375 mg iodine day 21 . These calculations are very close to Prof. Delange's estimated need for an extra 25 -150 mg day 21 of iodine, giving an RNI of 225-350 mg day 21 of iodine during lactation (Table 1) . The safety of the recommended higher dose Is there any risk of adverse effects of the recommended intake of 250-300 mg iodine day 21 during pregnancy? A Danish study, which examined the thyroid function of babies born to women in a population with an estimated iodine intake of 75 mg day 21 was compared with babies born to women who were supplemented with 150 mg day 21 of iodine to give an estimated total iodine intake of 225 mg day 21 . The study found a higher cord blood TSH in the supplemented group (9.00 vs. 7.07 mIU l 21 , P , 0.05) 5 . The investigators took this to be evidence that 'the foetal thyroid is sensitive to the inhibitory effects of iodine'. However, the concentration of free T 4 in cord blood was higher in neonates born to supplemented compared with unsupplemented mothers (12.5 vs. 11.7 pmol l 21 , P , 0.05), the concentrations of total T 4 and T 3 were similar, and the T 4 thyroglobulin concentration was lower (34.3 vs. 56.7 mg dl 21 , P , 0.001) 5 . These appear to be positive effects on the babies born to iodine supplemented mothers.