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Exploration of the safe upper level of iodine intake in euthyroid Chinese adults: a randomized double-blind trial.
MedLine Citation:
PMID:  22205314     Owner:  NLM     Status:  Publisher    
BACKGROUND: The beneficial health effects associated with Universal Salt Iodization are well known. Yet, little is known about the possible adverse health effects in people with high iodine intake and the safe daily intake upper limit in the Chinese population. OBJECTIVE: The objective of this study was to explore the safe upper level of total daily iodine intake among adults in China. DESIGN: A 4-wk, double-blind, placebo-controlled, randomized controlled trial was conducted in 256 euthyroid adults. Participants were randomly assigned to 12 intervention groups with various iodine supplement doses ranging from 0 to 2000 μg/d. Total iodine intake included iodine from both supplements and diet. Multiple outcome measures were used to evaluate possible adverse effects, including thyroid function, thyroid size, and urinary iodine. RESULTS: The mean iodine intake from the diets and salt intake of the participants were 105 ± 25 and 258 ± 101 μg/d, respectively. In comparison with the placebo group, all iodide-supplemented groups responded with significant increases in median urinary iodine concentrations (P < 0.05) and in thyroid-stimulating hormone concentration (P < 0.05). Thyroid volume decreased after 4 wk in the high-iodine intervention groups (1500-2000 μg). Subclinical hypothyroidism appeared in the groups that received 400 μg I (5%) and 500-2000 μg I (15-47%). CONCLUSIONS: This study showed that subclinical hypothyroidism appeared in the participants who took the 400-μg I supplement, which provided a total iodine intake of ∼800 μg/d. Thus, we caution against a total daily iodine intake that exceeds 800 μg/d in China and recommend further research to determine a safe daily upper limit.
Zhongna Sang; Peizhong Peter Wang; Zhaixiao Yao; Jun Shen; Beth Halfyard; Long Tan; Na Zhao; Yuntang Wu; Shuo Gao; Jian Tan; Jiayu Liu; Zupei Chen; Wanqi Zhang
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Publication Detail:
Type:  JOURNAL ARTICLE     Date:  2011-12-28
Journal Detail:
Title:  The American journal of clinical nutrition     Volume:  -     ISSN:  1938-3207     ISO Abbreviation:  -     Publication Date:  2011 Dec 
Date Detail:
Created Date:  2011-12-29     Completed Date:  -     Revised Date:  -    
Medline Journal Info:
Nlm Unique ID:  0376027     Medline TA:  Am J Clin Nutr     Country:  -    
Other Details:
Languages:  ENG     Pagination:  -     Citation Subset:  -    
Department of Nutrition and Food Hygiene, School of Public Health, Tianjin Medical University, Tianjin, China.
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