Analysis of Determinants of Dietary Iodine Intake of Adolescents from Northern Regions of Poland: Coastal Areas and Lake Districts

<b>Background/Objectives:</b> Iodine plays a central role in thyroid hormone synthesis and neurodevelopment. Its deficiency and excessive intake have been identified as risk factors for thyroid diseases and their consequences. The objective of the study was to analyze dietary iodine intake (dIi) and the factors that determine its intake among post-primary school students from northern Poland, specifically those from coastal areas and lake districts. <b>Methods:</b> The study was conducted on a sub-national sample of 3102 adolescents (1751 females and 1351 males) aged 14-20 years, recruited from schools located in the Northern (N) and North-Western (N-W) macroregions of Poland. Dietary iodine intake was assessed using the Iodine Dietary Intake Evaluation-Food Frequency Questionnaire. Based on the data obtained, the adequacy of the intake of this micronutrient was assessed. Statistical analysis was performed using the Shapiro-Wilk, U Mann-Whitney, and Kruskal-Wallis tests and Spearman's correlation analysis. <b>Results:</b> The median dIi was 66.83 µg daily, including 53 µg from natural sources. This value was below the recommended dietary allowance of 150 µg and below the estimated average requirement of 95 µg of iodine in 85% and 68% of the study participants, respectively. Milk and dairy products provided the highest iodine intake (26.4%). Iodine-enriched salt (16.2%) also significantly impacted iodine intake. However, 60% of respondents did not use iodized salt. The median iodine levels from natural sources were found to be low (dairy products: 15.02 µg, fish and fish products: 2.38 µg, and eggs: 2.10 µg). Dietary iodine intake was significantly lower in adolescents from the N than N-W macroregion of Poland (median: 65.63 vs. µg daily, 74.2 <i>p</i> < 0.001). However, dIi did not depend on sex (<i>p</i> = 0.10), age (<i>p</i> = 0.80), school location (<i>p</i> = 0.80), body mass index classification (<i>p</i> = 0.76), or iodine supplementation (<i>p</i> = 0.90). <b>Conclusions:</b> The study results indicate that insufficient iodine intake among adolescents in northern Poland can be attributed to a limited intake of iodine from natural food sources. A pressing need exists to closely monitor iodine intake and status among Polish adolescents and to implement nutritional education, focusing on the role of iodine, potential risks associated with iodine deficiency, and dietary sources of iodine.