Urinary Iodine Concentration is Inversely Associated with Thyroglobulin Antibodies

Abstract

Objective: Epidemiologic studies on the relationship between iodine and thyroid antibodies are inconsistent. Iodine nutrition, genetic, and environmental factors have been shown to modify the effects of iodine on thyroid autoimmunity. We investigated the relationship between urinary iodine concentration (UIC) and thyroglobulin antibodies (TgAbs) in individuals living in iodine-sufficient areas in this cross-sectional study. Methods: A total of 15,008 participants were recruited according to the age range of the population of China in our study. An oral questionnaire was administered to collect basic demographic information. Serum thyrotropin (TSH), thyroid peroxidase antibodies (TPOAbs), TgAbs, and UIC were measured, and thyroid ultrasonography was performed in all subjects. Participants were further divided according to the level of UIC and the status of TgAb, and logistic regression was applied to determine the relationship between UIC and TgAbs. Results: The median UIC of the study population was 205.23 (95% confidence interval [CI], 65.7 to 537.67) μg/L. A total of 17.6% of participants had UIC <100 μg/L. With the increase in UIC, the prevalence of positive TgAbs decreased gradually. UIC level was lowest in subjects with high TgAb titer (median, 182.36 μg/L; 95% CI, 52.88 μg/L to 506.71 μg/L) and highest in the TgAb-negative group (median, 207.16 μg/L; 95% CI, 66.94 μg/L to 538.72 μg/L). Multilinear correlation analysis showed that gender (β = 37.632; P<.001), age (β = 0.467; P = .038), TSH (β = 13.107; P<.001), TPOAb (β = 1.150; P<.001), thyroid volume (β = 2.883; P<.001), and UIC (β = -0.047; P = .032) were independent predictors of TgAb variations. Low UIC (<100 μg/L) was associated with increased risk of positive TgAbs (adjusted odds ratio = 1.255 [1.004 to 1.568]). Conclusion: Low UIC is an independent risk factor for positive TgAb in individuals living in iodine-sufficient areas. Abbreviations: CI = confidence interval; CV = coefficient of variation; FT3 = free triiodothyronine; FT4 = free thyroxine; OR = odds ratio; TgAb = thyroglobulin antibody; TPOAb = thyroid peroxidase antibody; TSH = thyrotropin; UIC = urinary iodine concentration; USI = universal salt iodization.