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

Clinical studies in Portugal have demonstrated the existence of a generalized deficiency in iodine of pregnant women and with school-age children. A general lack of awareness within the Portuguese population about the importance of iodine in the diet has also been identified. Thus, in this work we report the program underway in country to monitor the real content of iodine in school meals. Collection of foods from schools was designed to represent school meal program in place. Foods were organized into three groups. One hundred and forty four samples cooked with iodization salt (soup and main course) were collected from primary schools across Lisbon District (Group I). Twelve samples were used as reference of real iodine content from a pilot school (Group II). One hundred and forty four samples composed according consumption data were used as reference of minimum iodine value (Group III). A total of three hundred samples were analysed in pooled or single corresponding to thirty six laboratory samples and analysed in triplicate. The iodine contents were determined by 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, under the frame of ISO/EN 17025:2005 and EN 15111:2007. Laboratory performance was demonstrated through a successfully participated in Proficiency Testing Schemes launched by accredited provider. The concentration of iodine in analysed samples showed a wide range of levels varying according to the group. Group I from 9.9 µg/100g in chicken to 23.2 µg/100g in fish. Group II the highest value (32.3 µg/100g) was found in soup. The lowest value (below limit of quantification) was found in meat of Group III. The ratio between Group I and Group III was used to estimate effectiveness of the program, and the biggest difference was found in fish and narrowest was determine in chicken. The distance between iodine content in Group I and Group II was used to monitoring bias due to pooled samples. The major difference was observed in turkey. Sodium content is discussed as a contribution to clarify the iodine differences. Cooking procedure, iodization salt absorption, and operator performance were identified as main factors contributing to the differences between real and prescribed content. Iodization salt content determined in foods as consumed is an appropriate approach to evaluate fortification program and risks of both inadequate and excess iodine intake.

This work was supported with co-financing of World Health Organization (WHO) in the frame of project “WHO Collaborating Centre for Nutrition and Childhood Obesity”. The authors appreciate the financial support of Project PRO-METROFOOD.

N/A