Smaller Thyroid Gland Volume with High Urinary Iodine Excretion in Japanese Schoolchildren: Normative Reference Values in an Iodine-Sufficient Area and Comparison with the WHO/ICCIDD Reference

Abstract

Iodine deficiency disorders (IDDs) are serious global public health problems and approximately 2 billion people are at risk of IDD complications. Urine iodine and thyroid size by ultrasound in school-age children are important indicators for assessing IDD in a population. Interpretation of sonographically measured thyroid volume requires valid reference criteria from iodine-sufficient populations, and in 2003 WHO (World Health Organization)/ICCIDD (International Council for the Control of Iodine Deficiency Disorders) proposed new international reference values for thyroid volume in children aged 6-12 years. To establish a normative reference of thyroid volume and characterize the current status of iodine nutrition in Japanese schoolchildren in Tokyo, where iodine deficiency has never existed, a total of 654 subjects aged 6-12 years (317 girls and 337 boys) in three primary schools were enrolled in the study in 2002. Thyroid volume was determined by using the standardized method recommended by WHO/ICCIDD and the iodine concentration in spot urine samples and the anthropometric measurements were evaluated. Thyroid volume was positively correlated with the children's age, height, weight, or BSA. Regardless of gender the computed median and 97th percentile thyroid volumes based on age or BSA in Japanese children were generally lower than the corresponding values recently reported in iodine-sufficient areas, although these values were slightly higher (5-13%) than those in the 2003 WHO/ICCIDD international reference. The computed median value of urinary iodine concentration was 281.6 microg/L (303.7 microg/gCre) and extremely high values exceeding 1,000 microg/L were found in 16% of the subjects. The present study clearly indicated a high iodine intake in Japanese schoolchildren and also established reference values for thyroid volume that might be applicable to countries in the Far East as a population-specific local reference.

Gestational changes of thyroid function and urinary iodine in thyroid antibody-negative Japanese women

“…However, national survey data for iodine intake is not currently available because iodine is not included as a target nutrient in the national health and nutrition survey. According to our collaborative studies with WHO in Tokyo and Hokkaido, the median UI value in schoolaged children is 281 to 288μg/L, suggesting a sufficient iodine status with more than adequate iodine intake [35][36][37]. In addition, children with a high UI excretion and increased thyroid gland volume were observed in a coastal area of Hokkaido [37].…”

Systematic determination of thyroid volume by ultrasound examination from infancy to adolescence in Japan: The Fukushima Health Management Survey

“…After publishing these data, recent studies on thyroid volume confirmed the international reference values although the number of cases are small (approximately 200-5000 cases) in all studies [11][12][13][14][15][16]. In Japan, Fuse et al compared the international reference values for Japanese and thyroid volumes of approximately 1000 schoolchildren [11]. They con- NA denotes the data was not applicable.…”

Genetic alterations of differentiated thyroid carcinoma in iodine‐rich and iodine‐deficient countries

“…Zava and Zava 7 estimated that Japanese iodine intake, which comes largely from seaweed consumption, ranges from 1 to 3 mg/day. The mean or median UIC of Japanese residents ranges from 281 to 3300 μg/L in many regions of Japan 8, 9, 10, 11, 12, 13, 14.…”