Evaluation of Iodine Status among Korean Patients with Papillary Thyroid Cancer Using Dietary and Urinary Iodine

BACKGROUND: Concerns have been raised regarding thyroid disorders caused by excessive iodine in Koreans, who have iodine-rich diets. This study evaluated iodine status using dietary iodine intake and urinary iodine in papillary thyroid cancer (PTC) patients. METHODS: Dietary data of PTC patients were assessed using a 24-hour recall and food frequency questionnaire (FFQ), and urinary iodine concentrations (UICs) were also obtained. To compare the iodine status of PTC patients, Korean adults with or without thyroid disease from the Korea National Health and Nutrition Examination Survey, which had 24-hour recall data and urinary iodine measurements, were analyzed. RESULTS: The median daily iodine intake by 24-hour recall was 341.7 μg/day in PTC patients, similar to the levels of other Korean adults. Based on UICs, the prevalence of excessive iodine was 54.4% in PTC patients, which was similar to the prevalence among subjects with thyroid disease (55.4%) but slightly higher than that in subjects without thyroid disease (47.7%). Based on dietary iodine by 24-hour recall, the prevalence of excessive iodine intake was 7.2%, which was higher than that among subjects with (4.4%) or without (3.9%) thyroid disease. The dietary iodine intake based on 24-hour recall was closely correlated with the UIC (r=0.4826) in PTC patients, but dietary iodine by FFQ was not significantly correlated with either 24-hour recall or UIC-based dietary iodine. CONCLUSION: Excessive iodine intake was more common in PTC patients than in subjects without thyroid disease. Further longitudinal research is necessary to elucidate the role of dietary iodine in PTC.