Survey on the prevalence and related factors of thyroid disorders in different iodine intake regions in China in 2015-2017

Abstract

Objective: To observe the prevalence and related factors of thyroid diseases in different iodine intake areas from 2015 to 2017 after the implementation of national salt iodization policy in China for 20 years. Methods: A cross-sectional survey. Multi-stage stratified cluster random sampling was used to randomly select subjects meeting the inclusion criteria from 31 provinces, municipalities and autonomous regions in China from January 2015 to December 2017, and stratified by age and sex. The survey included questionnaire, physical examination and thyroid ultrasonography. At the same time, the concentrations of serum thyrotropin, thyroxine, thyroid peroxidase antibody (TPOAb), thyroid globulin antibody (TgAb) and urinary iodine were measured.To determine whether the patient has a certain thyroid disease according to the above results. Different iodine nutrition areas were defined according to urinary iodine concentration, and the influence of iodine nutrition status in different iodine intake areas on thyroid diseases was analyzed. Results: A total of 78 470 adults were included, including 39 893 in the area of moderate iodine, 28 779 in the area of adequate iodine, and 9 798 in the area of excessive iodine.In the above three regions, the prevalence of subclinical hyperthyroidism (hyperthyroidism) was 0.45% (95%CI: 0.39%-0.52%), 0.50%(95%CI: 0.35%-0.70%)and 0.27%(95%CI: 0.20%-0.35%), respectively, with statistical significance(χ²=6.92, P=0.003). The prevalence of subclinical hypothyroidism (hypothyroidism) was 11.36% (95%CI: 10.73%-12.02%), 13.57%(95%CI: 11.70%-15.69%) and 16.18%(95%CI: 12.41%-20.82%), respectively, with statistical significance(χ²=5.08, P=0.009). The prevalence rates of Graves' disease, TPOAb, goiter and thyroid nodule among the three regions were statistically significant (all P<0.05). There were no significant differences in the prevalence of clinical hyperthyroidism and clinical hypothyroidism and the positive rate of TgAb among the three regions (all P>0.05). Multivariate logistic regression model analysis showed that excess iodine was a risk factor for subclinical hypothyroidism (OR=1.24, 95%CI: 1.06-1.44), and a protective factor for thyroid nodules (OR=0.73, 95%CI: 0.57-0.94). Iodine overdose was a risk factor for subclinical hypothyroidism (OR=1.47, 95%CI: 1.08-2.01), while it was a protective factor for subclinical hyperthyroidism (OR=0.56, 95%CI: 0.41-0.77), and TPOAb positive (OR=0.93, 95%CI: 0.87-0.99), goiter (OR=0.33, 95%CI: 0.17-0.66) and thyroid nodule (OR=0.77, 95%CI: 0.61-0.97). Conclusions: There are significant differences in the prevalence of subclinical hyperthyroidism, subclinical hypothyroidism, positive TPOAb, thyroid nodule and goiter in different iodine intake regions. Different iodine intake levels have an effect on the incidence of thyroid diseases.