Do Brazilian Pregnant Women Need Iodine Supplementation? A Commentary on the Latest American Thyroid Association Guideline

Abstract

Iodine is an essential micronutrient required for the production of thyroid hormones, which are critical for homeostasis and neurodevelopment. Because of increased thyroid hormone production, renal iodine excretion and fetal iodine requirements, dietary iodine requirements are higher in pregnancy than they are for nonpregnant adults. 1 Based on this, the World Health Organization (WHO) and the American Thyroid Association (ATA) recommend a daily iodine intake of 250 µg for pregnant and lactating women. 2,3 Iodine deficiency disorder (IDD) in pregnant women could result in harmful effects, including goiter, cretinism, hypothyroidism, growth retardation, pregnancy loss, and infant mortality. Moreover, inadequate iodine intake during pregnancy may lead to neurodevelopmental deficits in offspring, and iodine deficiency is currently considered the leading preventable cause of intellectual impairment worldwide. 4 On the other hand, the excess of iodine may result in fetal goiter and hypothyroidism. Exposures as minor as the vaginal application of povidone-iodine during delivery or local use of disinfectant in newborns can lead to increased serum TSH concentrations 5 and transient neonatal hypothyroidism. 6 With this information in mind, we read with great interest the 2017 Guidelines of the American Thyroid Association for the Diagnosis and Management of Thyroid Disease during Pregnancy and the Postpartum. 7 Among other topics, the nutritional aspects related to iodine sufficiency are addressed in section IV, and a supplementation with 150 μg of potassium iodine per day is suggested on Recommendation 6 for women, in most regions of the world, who are planning a pregnancy or currently pregnant. This is optimally started 3 months in advance of planned pregnancy (strong recommendation, moderate-quality evidence). Could this recommendation improve the quality of the prenatal care of Brazilian pregnant women?The most efficient method of IDD prevention is salt iodination. Also, ongoing monitoring of population biomarkers, such as urinary iodine concentration, is essential to ensure that population iodine intakes are optimized. In Brazil, the salt iodination is controlled by federal law in partnership with the National Agency for Sanitary Surveillance (Anvisa, in the Portuguese acronym) and the salt productive sector. 8-10 Unfortunately, data on the iodine nutritional status are scarce and contradictory in Brazil. The national project of salt iodination (PNAIsal, in the Portuguese acronym) (which evaluated 477 locations and a total of 18,978 school children) identified Brazil as a country of "more than appropriate" iodine consumption, with a mean urinary iodine excretion (UIE) concentration of 276 µg/L. 11,12 A recent meta-analysis concluded that the majority of the data on this subject are derived from the population in the south/southeast region of Brazil, but the actual overall IDD prevalence is unknown and might still be high in some areas. 13 Regarding the pregnant population, three studies were published prior to Anvis...