Objective   To investigate the prevalence of thyroid disorders, iodine nutritional status and relevant risk factors among adults in Chengdu city on the basis of two population-based surveys, one conducted between 2016 and 2017 and the other, between 2019 and 2020, and to provide references for making health-related administrative decisions.

  Methods   Two population-based sampling surveys were conducted. The first one was done between October 2016 and December 2017, using stratified cluster random sampling to select subjects from 2 urban and 2 rural communities in Chengdu. Then, between December 2019 and February 2020, sequential cluster sampling was used to select subjects from communities in the peripheral regions of Longquanyi District, Chengdu. Both surveys covered natural populations of people who were 18 or older and who met the inclusion criteria. In the first survey, questionnaires, physical examination, thyroid ultrasound, and examinations of serum thyroid biochemical markers and urine iodine were performed, while in the second survey, only questionnaire concerning thyroid disorders and physical examination were performed. Statistical analysis of the nutritional status of iodine, the prevalence of thyroid disorders, and potential risk factor was conducted.

  Results   A total of 1859 subjects were enrolled for the first survey and 16152 for the second. According to the results of the first survey, the median urine iodine concentration was 172.10 μg/L, and the group with adequate or more than adequate iodine accounted for more than 60% of the surveyed population. The prevalence of thyroid disorders was found to be 0.48% for overt hyperthyroidism, 0.43% for subclinical hyperthyroidism, 0.43% for Grave's disease, 1.34% for overt hypothyroidism, 16.62% for subclinical hypothyroidism, 16.73% for positive thyroid antibody, 12.96% for TPOAb positive, 10.06% for TGAb positive, 0.81% for goiter, 14.85% for single nodule, 14.42% for multi-nodules, and 29.26% for thyroid nodules. Excess iodine is a risk factor for subclinical hypothyroidism (OR=1.50, 95% confidence interval CI: 1.07-2.10, P<0.05), and iodine deficiency is a risk factor for multiple thyroid nodules (OR=1.45, 95% CI: 1.02-2.05, P<0.05). The total prevalence of hyperthyroidism, hypothyroidism and Hashimoto's thyroiditis in the two surveys was 6.58% and 5.95%, respectively, showing no significant difference. The second survey lacked accurate data on thyroid nodules.

  Conclusion   The iodine nutritional status of adults in Chengdu in recent years was appropriate. The total prevalence of hyperthyroidism, hypothyroidism and Hashimoto's thyroiditis remained stable, while that of thyroid nodule increased in recent years. We should continue with the implementation of the universal salt iodization policy and reinforce efforts in monitoring. Furthermore, we should make an active effort to look into the etiology of thyroid nodules.