Endocrine Abstracts

Japan has been regarded as a nongoitorous country due to the regular intake of iodine-rich food. However, nationwide information on current status of iodine intake is not available because there is no survey system for iodine nutrition in Japan.

Objective: The objectives of this study is to characterize current iodine status in Japan.

Methods: Since 2002 we have conducted studies on iodine nutrition in the Metropolitan area including Tokyo, Chiba and Kanagawa prefectures. Spot urine samples were collected in healthy subjects without known thyroid diseases and urinary iodine concentration (UIC) was measured by the ammonium persulfate digestion on microplate method based on the Sandell Kolthoff reaction. Serum TSH, free thyroxin and thyroid autoantibodies were measured if blood samples are available. Dietary iodine intake (DII) was assessed by using an iodine-specific food frequency questionnaire developed and verified by us.Iodine content was calculated on the basis of data from the standard tables of food composition in Japan 2010.

Results: Median UICs according to age groups are summarized in the table. Median daily DII in healthy adults was 471.0 μg /day (IQR:256.7, 859.8) and there was no significant difference in DII value between male (453.1 μg /day) and female (503.5 μg /day). The questionnaire data correlated well with urinary iodine excretion (Spearman r=0.32).

Conclusion: According to WHO/ICCIDD criteria for iodine deficiency disease median UICs of 100–199 μg/L at population level indicate adequate iodine intake and optimal nutrition and the median UIC over 300 μg/L in local schoolchildren is regarded as excessive. Our results indicate that current iodine status in Japanese is sufficient, not excessive, although the data is local.

Declaration of interest: The authors declare that there is no conflict of interest that could be perceived as prejudicing the impartiality of the research project.

Funding: This work was supported, however funding details unavailable.