A 1:1 matched case-control study: Are thyroid nodules related to iodine nutrition? Can Tg serve as a functional biomarker for thyroid nodules?

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Abstract Background:To eliminate the harm induced by iodine deficiency, a strategy of universal salt iodization (USI) is adopted. During this period, it shows a significant increasing trend in the prevalence of thyroid nodules, resulting in shining a spotlight on whether thyroid nodules are related to the level of iodine nutrition. In this study, a 1:1 matched case-control study is conducted to investigate whether thyroid nodules are related to the level of iodine nutrition and whether there are differences in thyroid function indicators. And other influencing factors of thyroid nodules are further explored. Methods:Villages with median urinary iodine (MUI) <100μg/L, 100-199μg/L, and 200-299μg/L in general population were selected as the survey sites. The residents who have lived there for more than 5 years with thyroid nodules tested by B-ultrasound were the case group, while those without nodules found by B-ultrasound examination were the control group that matched 1:1 with the case group by age (±3 years), gender and region. All subjects completed questionnaires, collected blood and urine samples to detect the thyroid function indicators and urinary iodine concentration. Results: There was no statistically significant difference in the MUI between the case group and the control group in the areas with adequate iodine intake, the areas with mild iodine deficiency(P>0.05); The MUI of the case group in the areas where iodine intake was more than adequate was lower than that of the control group(P<0.05); The case group’s levels of Tg and FT4 in both areas with mild iodine deficiency and more than adequate iodine intake were higher than those of the control group, whereas only the level of Tg of the case group was higher than that of the control group in the areas with adequate iodine intake, meaning that the difference was statistically significant (P<0.05); Other indicators had no statistical significance. The conditional Logistic regression model fitted by Enter method resulted that there were statistically significant correlations between history of thyroid disorders, Tg, TgAb and thyroid nodules. Conclusions: On the one hand, there was no statistical correlation between the iodine nutrition and thyroid nodules in the areas with adequate iodine intake and areas with mild iodine deficiency. On the other hand, in the areas with more than adequate iodine intake, the urine iodine concentration in the nodule group was lower than that in the non-nodule group, which indicates that when the urine iodine concentration is 200-299 μg/L, a slight increase in urinary iodine may help inhibit the occurrence of nodules. History of thyroid disorders and increased Tg and TgAb levels were risk factors for thyroid nodules. Tg can serve as a functional biomarker for thyroid nodules.

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