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Efficacy and Safety of Long-Term Universal Salt Iodization on Thyroid Disorders: An Epidemiological Evidence from 31 Provinces of Mainland China
Shandong First Medical University - Science and Technology Innovation Center; Shandong First Medical University - Department of Endocrinology and Metabolism; Shandong Academy of Clinical Medicine - Institute of Endocrinology; Shandong Clinical Medical Center of Endocrinology and Metabolism
Background: The mandatory universal salt iodization (USI) program has been implemented in China for twenty years. Although iodine deficiency disorders are effectively controlled, the dangers of excess iodine have been debated.
Methods: A nationally representative cross-sectional study of 78,470 participants, aged 18 or older, were enrolled from all 31 provincial regions of mainland China. The participants were given a questionnaire and B-mode ultrasonography on the thyroid. Serum concentrations of thyroid hormones, thyroid antibodies and urine iodine concentration (UIC) were measured.
Findings: The median UIC of school-age children was 199·75µg/L. The weighted prevalence of the thyroid disorders in adults were as follows: 0·78% of overt hyperthyroidism, 0·44 % of subclinical hyperthyroidism, 0·53% of Graves’ disease, 1·02% of overt hypothyroidism, 12·93% of subclinical hypothyroidism, 14·19% of autoimmune thyroiditis, 10·19% of positive TPOAb, 9·70% of positive TgAb, 1·17% of goiter and 20·43 % of thyroid nodules. Iodine excess was only associated with higher odds of overt hyperthyroidism and subclinical hypothyroidism, while iodine deficiency was significantly associated with higher odds of most thyroid disorders. In addition, increased iodine intake was significantly associated with elevated serum TSH levels, but was inversely associated with thyroid antibodies and thyroid nodule.
Interpretation: The long-term mandatory USI program is not only effective for iodine deficient disorders but also safe for prevalence of thyroid disorders based on a sufficient iodine status of pre-USI. The risk of iodine deficiency outweighs that of iodine excess.
Funding Statement: Research Fund for Public Welfare from National Health and Family Planning Commission of China.
Declaration of Interests: All authors declare no competing interests.
Ethics Approval Statement: The research protocols were approved by the Medical Ethics Committee of China Medical University. All subjects were provided written informed consent following a thorough explanation of the research procedures.
Keywords: Iodine; Thyroid disorders; Universal salt iodization; China; Prevalence
Li, Yongze and Ba, Jianming and Chen, Bing and Du, Jianling and He, Lanjie and Lai, Xiaoyang and Teng, Xiaochun and Teng, Di and Shi, Xiaoguang and Li, Yanbo and Chi, Haiyi and Liao, Eryuan and Liu, Chao and Liu, Libin and Qin, Guijun and Qin, Yingfen and Quan, Huibiao and Shi, Bingyin and Sun, Hui and Tang, Xulei and Tong, Nanwei and Wang, Guixia and Zhang, Jin-an and Wang, Youmin and Xue, Yuanming and Yan, Li and Yang, Jing and Yang, Lihui and Yao, Yongli and Ye, Zhen and Zhang, Qiao and Zhang, Lihui and Zhu, Jun and Zhu, Mei and Ning, Guang and Mu, Yiming and Zhao, Jiajun and Shan, Zhongyan and Teng, Weiping, Efficacy and Safety of Long-Term Universal Salt Iodization on Thyroid Disorders: An Epidemiological Evidence from 31 Provinces of Mainland China (April 1, 2019). Available at SSRN: https://ssrn.com/abstract=3310617 or http://dx.doi.org/10.2139/ssrn.3310617
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