Evaluation of iodine content in Portuguese primary school meals after mandatory iodization program

Iodine is an essential trace element in the human and animal diets. The major role of thyroid hormones is related to the growth and development of the body. Iodine deficiency is the most common cause of preventable mental impairment. There are, in Portugal, a widespread deficiency of iodine of pregnant women and school-age children [1 - 3]. The aim of this study was monitored the real content of iodine in school meals. Collection of foods from schools was designed to represent school meal program based on three hundred samples organized into three groups. Group I contained one hundred and forty-four samples cooked with iodized salt from primary schools across the Lisbon metropolitan area. Group II had twelve samples from a pilot school. This school was used as a reference for real iodine content. Group III was constituted by one hundred and forty-four samples used as a standard for minimum iodine value. These samples were collected based on consumption patterns from national food consumption surveys. Based on ISO/EN 17025:2005 and EN 15111:2007, the determination of iodine content was performed using inductively coupled plasma-mass spectrometry (ICP-MS) after alkaline extraction with TMAH (tetramethylammonium hydroxide) in a graphite block system during 3 hours at 90 °C. The concentration of iodine in samples showed a wide range of levels, e.g., Group I from 5.3 µg/100 g in pasta to 52 µg/100 g in cod and Group II the highest value (32 µg/100 g) in soup. The lowest value (< 1.9) was found in the meat of Group III. The ratio between Group I and Group III was used to estimate the effectiveness of the program, and the biggest difference was found in fish and lowest was determined in soup. The difference between iodine content in Group I and Group II was used to monitoring the use of iodized salt in the other schools from Lisbon metropolitan area. The cooking procedure, iodization salt absorption, and operator performance were identified as the main factors contributing to the differences between real and prescribed content. This study demonstrates that the determination of iodine content in foods cooked with and without iodized salt is an appropriate approach to evaluate fortification program and risks of both inadequate and excess iodine intake.

The scientific work was funded by the Project WHO Collaborating Centre funded by the Instituto Nacional de Saúde Doutor Ricardo Jorge, I.P. Lisbon, Portugal (2013DAN850) and by the PRO-METROFOOD project, funded by European Union’s Horizon 2020 research and innovation programme under grant agreement No 739568

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