Urinary iodine concentration and thyroid hormones: Korea National Health and Nutrition Examination Survey 2013-2015

PurposeAn epidemiologic study that evaluated population's iodine nutrition status and its relationship with thyroid hormones is lacking in iodine-sufficient area. This nationwide study aimed to evaluate the iodine nutrition status in Korea and relationship between urine iodine concentration (UIC) and thyroid hormones.MethodsA total of 8318 subjects of the Korea National Health and Nutrition Examination Survey VI (2013-2015) with UIC and thyroid hormone evaluation were included. Median UIC level and estimated 24-h iodine intake were calculated. The prevalence of iodine deficiency or excess was obtained using estimated average requirement or above the tolerable upper intake level cut-point method by estimated iodine intake. We analyzed UIC with regard to age, sex, social economic status, and geographic characteristics.ResultsThe median UIC in general population and estimated iodine intake in adult population were 293.9g/L (above requirement according to World Health Organization classification) and 249.3g/day, respectively. The prevalence of iodine deficiency and excess was 14.0 and 13.4%. The median UIC was higher among SAC [511 (299.9-948.5)] and lower among seventies [251.2 (98.9-761.6)] compared to other age groups. The median UIC increased with household income level (p for trend<0.001). The subjects living in rural and inland region had lowest UIC among the enrolled subjects. The subgroups with higher median UIC were associated with higher mean TSH levels.ConclusionsThis first nationwide study in Korea demonstrated that the median of UIC and estimated iodine intake lie at nearly 300 mu g/L and 250 mu g/day, respectively, which shows an overall excellent iodine nutrition.