High iodine intake by preschool children in Miyagi prefecture, Japan

Abstract

Objectives: Standard Tables of Food Composition in Japan 2010 (FCT) remain incomplete for iodine contents. This survey was initiated to develop a method to cope with this shortage and to find daily iodine intake of preschool children in Japan.

Methods: Data were available for one-day food intake for 296 3- to 6-year-old children (the total cases). 128 samples (the selected cases) were analyzed by ICP-MS for iodine (the measured values). Iodine intake was also calculated using FCT assuming that iodine contents in missing items were zero (the calculated values).

Results: Measured and calculated values for the selected 125 cases (after exclusion of 3 extreme cases) gave geometric means (GM) of 117.6 and 101.8 μg/day. The measured/calculated ratio in GM, 117.6/101.8 = 1.155, was applied to the calculated values for total 296 cases to estimate iodine intake (the estimated values). GM for the estimated value was 175.2 μg/day and it was 8.93 μg/kg/day after adjustment for body weight for 296 children. There was no significant difference between boys and girls.

Discussion: The GM values for both the measured and estimated values (n = 125 pairs) were 117.6 μg/day. The agreement suggested that the factor employed, 1.155, was proper and adequate. Literature survey suggested that values on a body weight basis were comparable between the children and adults in Japan. The levels were higher than levels in east Asian countries.

Conclusions: A correction method was developed for estimation of daily dietary iodine intake. The iodine intake level for preschoolers was comparable to levels for adult population.

Figures

Fig. 1

Distribution histograms of a measure values b calculated values and c estimated values (after logarithmic conversion) for 125 selected cases. d shows the distribution of a total 296 cases. The horizontal axes show the values after logarithmic conversion; the values are in μg/day. The curves show normal distribution

Fig. 2

Correlation between 125 pairs of measured values and calculated values after logarithmic conversion. Each dot shows one case and the line in the middle is a calculated regression line of Y = 1.02 + 0.48X (r = 0.442, p < 0.01), where X and Y are log measured and calculated values (both in μg/day), respectively. The dotted curves on both sides of the regression line show the 95 % limit of the means