Effect of iodine intake on thyroid diseases in China.

Abstract

BACKGROUND Iodine is an essential component of thyroid hormones; either low or high intake may lead to thyroid disease. We observed an increase in the prevalence of overt hypothyroidism, subclinical hypothyroidism, and autoimmune thyroiditis with increasing iodine intake in China in cohorts from three regions with different levels of iodine intake: mildly deficient (median urinary iodine excretion, 84 microg per liter), more than adequate (median, 243 microg per liter), and excessive (median, 651 microg per liter). Participants enrolled in a baseline study in 1999, and during the five-year follow-up through 2004, we examined the effect of regional differences in iodine intake on the incidence of thyroid disease. METHODS Of the 3761 unselected subjects who were enrolled at baseline, 3018 (80.2 percent) participated in this follow-up study. Levels of thyroid hormones and thyroid autoantibodies in serum, and iodine in urine, were measured and B-mode ultrasonography of the thyroid was performed at baseline and follow-up. RESULTS Among subjects with mildly deficient iodine intake, those with more than adequate intake, and those with excessive intake, the cumulative incidence of overt hypothyroidism was 0.2 percent, 0.5 percent, and 0.3 percent, respectively; that of subclinical hypothyroidism, 0.2 percent, 2.6 percent, and 2.9 percent, respectively; and that of autoimmune thyroiditis, 0.2 percent, 1.0 percent, and 1.3 percent, respectively. Among subjects with euthyroidism and antithyroid antibodies at baseline, the five-year incidence of elevated serum thyrotropin levels was greater among those with more than adequate or excessive iodine intake than among those with mildly deficient iodine intake. A baseline serum thyrotropin level of 1.0 to 1.9 mIU per liter was associated with the lowest subsequent incidence of abnormal thyroid function. CONCLUSIONS More than adequate or excessive iodine intake may lead to hypothyroidism and autoimmune thyroiditis.

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@article{Teng2006EffectOI, title={Effect of iodine intake on thyroid diseases in China.}, author={Weiping Teng and Zhongyan Shan and Xiaochun Teng and Hai-xia Guan and Yushu Li and Di Teng and Ying Jin and Xiaohui Yu and Chenling Fan and Wei Yee Chong and Fan Yang and Hong Dai and Yang Yu and Jia Li and Yanyan Chen and Dong Zhao and Xiaoguang Shi and Fengnan Hu and Jinyuan Mao and Xiaolan Gu and Rong Yang and Yajie Tong and Weibo Wang and Tian-shu Gao and Chenyang Li}, journal={The New England journal of medicine}, year={2006}, volume={354 26}, pages={2783-93} }