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

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 saf...

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Published in:The journal of clinical endocrinology and metabolism 2015-04, Vol.100 (4), p.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: Article
Language:English
Subjects:
Adult
China - epidemiology
Cross-Sectional Studies
Female
Humans
Hypothyroidism - epidemiology
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 - blood
Thyrotropin - blood
Thyroxine - blood
Young Adult
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Summary: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.
ISSN:0021-972X
1945-7197
DOI:10.1210/jc.2014-3704