Iodine Status and Prevalence of Thyroid Disorders after Introduction of Mandatory Universal Salt Iodization for 16 Years in China: A Cross-Sectional Study in 10 Cities

Wednesday, 17th of August 2016

Thyroid. 2016 Aug;26(8):1125-30. doi: 10.1089/thy.2015.0613. Epub 2016 Jul 22.

Iodine Status and Prevalence of Thyroid Disorders after Introduction of Mandatory Universal Salt Iodization for 16 Years in China: A Cross-Sectional Study in 10 Cities

Shan Z¹, Chen L², Lian X³, Liu C⁴, Shi B⁵, Shi L⁶, Tong N⁷, Wang S⁸, Weng J⁹, Zhao J¹⁰, Teng X¹, Yu X¹, Lai Y¹, Wang W¹, Li C¹, Mao J¹, Li Y¹, Fan C¹, Teng W¹.

Author information

¹1 Department of Endocrinology and Metabolism, Key Laboratory of Thyroid Diseases in Liaoning Province, The First Hospital of China Medical University , Shenyang, China .
²2 Department of Endocrinology, Union Hospital, Tongji Medical College, Huazhong University of Science and Technology , Wuhan, China .
³3 Department of Endocrinology, Beijing Union Medical College Hospital , Beijing, China .
⁴4 Department of Endocrinology, Jiangsu Province Hospital on Integration of Chinese and Western Medicine , Nanjing, China .
⁵5 Department of Endocrinology, First Affiliated Hospital of Medical College of Xian Jiaotong University , Xian, China .
⁶6 Department of Endocrinology, Affiliated Hospital of Guiyang Medical College , Guiyang, China .
⁷7 Department of Endocrinology, West China hospital, Sichuan University , Chengdu, China .
⁸8 Department of Endocrinology, The Ruijin Hospital of Shanghai Jiaotong University , Shanghai, China .
⁹9 Department of Endocrinology, The Third Affiliated Hospital of Sun Yat-sen University , Guangzhou, China .
¹⁰10 Department of Endocrinology, The Provincial Hospital Affiliated to Shandong University , Jinan, China .

Abstract below; full text is at http://online.liebertpub.com/doi/10.1089/thy.2015.0613

BACKGROUND:

The goal of eliminating iodine deficiency worldwide was successfully achieved in China after the implementation of a mandatory universal salt iodization program for the last 16 years. Thus, China has been assessed as a country with more than adequate iodine levels. This survey aimed to investigate the current iodine status in China and the effects of an increased iodine intake on the spectrum and prevalence of thyroid disorders.

METHODS:

A total of 15,008 adult subjects from 10 cities in eastern and central China were investigated. Serum thyrotropin (TSH), thyroid peroxidase antibodies (TPOAb), thyroglobulin antibodies (TgAb), and urine iodine concentration (UIC) were measured, and an ultrasonography of the thyroid was performed in all subjects. Free thyroxine (fT4) and free triiodothyronine (fT3) levels were only measured if the serum TSH was outside the normal range.

RESULTS:

The median UIC values were 197 μg/L in school-age children (SAC) and 205 μg/L in a cohort population. Six cities were classified as regions with adequate iodine intake (AII), and four cities as regions with more than adequate iodine intake (MTAII), according to median SAC UIC. The prevalence of clinical hypothyroidism, subclinical hypothyroidism, and positive thyroid antibodies was significantly higher in MTAII cities than it was in AII cities. Moreover, the prevalence of clinical hyperthyroidism (1.1% vs. 0.8%, p = 0.033) and Graves disease (0.8% vs. 0.5%, p = 0.019) also significantly increased in MTAII cities. Compared with a five-year prospective study conducted in 1999, the prevalence of goiter significantly decreased (2.9% vs. 5.02%, p = 0.001), but there was a significant increase in thyroid nodules (12.8% vs. 2.78%, p = 0.001). The prevalence of subclinical hypothyroidism (16.7% vs. 3.22%), positive TPOAb (11.5% vs. 9.81%), and positive TgAb (12.6% vs. 9.09%) significantly increased, while no changes were seen in clinical hyperthyroidism, subclinical hyperthyroidism, or Graves disease.

CONCLUSION:

The goal of eliminating iodine deficiency has been successfully achieved in China. However, the prevalence and spectrum of thyroid disorders has increased, reflecting possible adverse effects of increased iodine intake.

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