High iodine intake by preschool children in Miyagi prefecture, Japan

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.

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).

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.

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.

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.