Special articleIodine supplementation during pregnancy and lactation. Position statement of the Working Group on Disorders Related to Iodine Deficiency and Thyroid Dysfunction of the Spanish Society of Endocrinology and NutritionSuplementación con yodo durante el embarazo y la lactancia. Toma de posición del Grupo de Trabajo de Trastornos relacionados con la Deficiencia de Yodo y Disfunción Tiroidea de la Sociedad Española de Endocrinología y Nutrición☆
Introduction
On October 30, 2012, a workshop on “Iodine and folic acid supplementation during pregnancy and lactation” organized by the Directorate of Public Health of the Basque Government and the Directorate General of Research and Public Health of the Valencian Government was held in Bilbao, Spain. The final recommendations of this workshop (BW)1 included the following conclusion, based on the statement that iodine contents of iodinated salt (IS), milk, and dairy products are sufficient to cover iodine requirements in pregnancy and lactation provided the mother takes these products adequately: “Universal supplementation with (potassium iodide) tablets during pregnancy and breast-feeding is not currently justified in Spain”. Thus, according to the conclusions of the workshop, pharmacological iodine supplementation during pregnancy and lactation should be selective, and should only be prescribed to women at a high risk of inadequate iodine intake or the development of thyroid dysfunction at these stages.1
Less than three weeks before the BW, the journal Endocrinología y Nutrición had published an editorial signed by the Working Group on Disorders Related to Iodine Deficiency and Thyroid Dysfunction (IDD-TD) entitled “Eradication of iodine deficiency in Spain. Close but not there yet”.2 This article alerted its readers to the risk that the currently adequate iodine nutritional status in Spanish children and adults, mainly achieved through silent or uncontrolled iodine prophylaxis, could change and iodine deficiency (ID) could reappear, as has recently occurred in other European countries.3
Because of the almost simultaneous dissemination of two documents proposing conflicting strategies for ID correction, our Working Group on IDD-TD considered it indispensable to analyze the BW document, disseminated by electronic means, not published in any scientific journal, and which has not been explicitly endorsed either by the Working Group on IDD-TD as such, or by other scientific bodies (Spanish Society of Gynecology and Obstetrics, Spanish Society of Family and Community Medicine, Spanish Society of Rural and General Practitioners, Spanish Society of General Practitioners, Spanish Pediatrics Society) whose members are implicated in the management of iodine supplementation to pregnant or lactating women.
This article analyzes changes over time in the correction of gestational ID in Spain and reviews the evidence available on iodine supplementation in pregnant and lactating women, taking into account that iodine requirements in these two groups are almost double those of the remaining adult population.
Section snippets
Changes over time in iodine deficiency in Spain
After more than four decades of documented ID in Spain, in 2004 the World Health Organization (WHO) included Spain among the countries with optimum iodine nutrition.4 Several recent studies conducted in schoolchildren,5 adults,6 and pre-schoolchildren7 show median urinary iodine levels higher than 100 μg/L confirming iodine sufficiency in those groups of the Spanish population. However, as reported by some authors8 in similar circumstances to those found in Spain, pregnant women may still have
Limitations of standard iodine prophylaxis for the correction of iodine deficiency during pregnancy and lactation
Pregnant women experience a number of physiological changes in iodine metabolism, including increased urinary iodine excretion, iodine transfer from maternal circulation to the fetoplacental unit, and increased iodine requirements of the fetal thyroid gland from the second half of pregnancy.30 Daily iodine requirements also increase during lactation due to iodine concentration in breast milk.31
In the general population, the routine use of IS, either individually (if present in more than 90% of
Benefits and risks of pharmacological iodine supplementation
In pregnant women, a lack of iodine in their diet leads to an ID status that subsequently affects the fetus. Under these circumstances, maternal hypothyroxinemia, negatively affecting fetal brain development and aggravated by fetal hypothyroidism, occurs.39 Cretinism represents the most severe form of the broad spectrum of developmental changes of the central nervous system caused by maternal ID, with various grades of intellectual impairment depending on ID severity.40 Many epidemiological
Recommendations of professional bodies for the prevention and correction of iodine deficiency during pregnancy and lactation
Ideally, standard iodine prophylaxis measures such as routine IS consumption should ensure the adequate replenishment of thyroid iodine deposits before pregnancy. However, as previously discussed, the current situation in Spain and most other European countries is far from this ideal situation.26 During the past decades, there has been a gradual decrease in dietary iodine intake in most Western countries related, among other factors, to the decreased iodine contents of dairy products,
Conclusions
The correction of ID in Spain achieved in 2004, mainly through silent or uncontrolled iodine prophylaxis, has failed to decrease the risk of ID in pregnant and lactating women. A similar situation is found in virtually all Spanish regions. The proven lack of efficacy of iodine prophylaxis through iodine intake in the food chain to correct ID in the pregnant population, despite the fact that Spain was already among the countries with an optimum iodine nutrition, prompted the recommendation of
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Please cite this article as: Donnay S, Arena J, Lucas A, Velasco I, Ares S, en nombre del Grupo de Trabajo sobre Trastornos relacionados con la Deficiencia de Yodo y Disfunción Tiroidea de la Sociedad Española de Endocrinología y Nutrición. Suplementación con yodo durante el embarazo y la lactancia. Toma de posición del Grupo de Trabajo de Trastornos relacionados con la Deficiencia de Yodo y Disfunción Tiroidea de la Sociedad Española de Endocrinología y Nutrición. Endocrinol Nutr. 2014;61:27–34.