Optimal and Safe Upper Limits of Iodine Intake for Early Pregnancy in Iodine-Sufficient Regions: A Cross-Sectional Study of 7190 Pregnant Women in China

• Published in: The journal of clinical endocrinology and metabolism Vol. 100; no. 4; pp. 1630 - 1638
• Main Authors: Shi, Xiaoguang, Han, Cheng, Li, Chenyan, Mao, Jinyuan, Wang, Weiwei, Xie, Xiaochen, Li, Chenyang, Xu, Bin, Meng, Tao, Du, Jianling, Zhang, Shaowei, Gao, Zhengnan, Zhang, Xiaomei, Fan, Chenling, Shan, Zhongyan, Teng, Weiping
• Format: Journal Article
• Language: English
• Published: United States Oxford University Press 01.04.2015; Copyright by The Endocrine Society
• Subjects: Adult; China - epidemiology; Cross-Sectional Studies; Female; Humans; Hypothyroidism; Hypothyroidism - epidemiology; Iodine; Iodine - administration & dosage; Iodine - adverse effects; Iodine - urine; Lactation - metabolism; Maternal Nutritional Physiological Phenomena; Pregnancy; Pregnancy Complications - epidemiology; Pregnancy Complications - prevention & control; Prevalence; Recommended Dietary Allowances; Thyroglobulin; Thyroglobulin - blood; Thyroid; Thyroid gland; Thyroid-stimulating hormone; Thyrotropin - blood; Thyroxine; Thyroxine - blood; Young Adult; China
• ISSN: 0021-972X; 1945-7197; 1945-7197
• DOI: 10.1210/jc.2014-3704

Context:The WHO Technical Consultation recommends urinary iodine concentrations (UIC) from 250 to 499 μg/L as more-than-adequate iodine intake and UIC ≥500 μg/L as excessive iodine for pregnant and lactating women, but scientific evidence for this is weak.Objective:We investigated optimal and safe ranges of iodine intake during early pregnancy in an iodine-sufficient region of China.Method:Seven thousand one hundred ninety pregnant women at 4–8 weeks gestation were investigated and their UIC, serum thyroid stimulating hormone (TSH), free thyroxine (FT4), thyroid-peroxidase antibody (TPOAb), thyroglobulin antibody (TgAb), and thyroglobulin (Tg) were measured.Results:The prevalence of overt hypothyroidism was lowest in the group with UIC 150–249 μg/L, which corresponded to the lowest serum Tg concentration (10.18 μg/L). Prevalences of subclinical hypothyroidism (2.4%) and isolated hypothyroxinemia (1.7%) were lower in the group with UIC 150–249 μg/L. Multivariate logistic regression indicated that more-than-adequate iodine intake (UIC 250–499 μg/L) and excessive iodine intake (UIC ≥ 500 μg/L) were associated with a 1.72-fold and a 2.17-fold increased risk of subclinical hypothyroidism, respectively. Meanwhile, excessive iodine intake was associated with a 2.85-fold increased risk of isolated hypothyroxinemia. Moreover, the prevalence of TPOAb positivity and TgAb positivity presented a U-shaped curve, ranging from mild iodine deficiency to iodine excess.Conclusion:The upper limit of iodine intake during early pregnancy in an iodine-sufficient region should not exceed UIC 250 μg/L, because this is associated with a significantly high risk of subclinical hypothyroidism, and a UIC of 500 μg/L should not be exceeded, as it is associated with a significantly high risk of isolated hypothyroxinemia.