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of goiter is approximately 100 μg/L. This approach can be used for estimating the RDA because it estimates the requirement for approximately 98 percent of the population. As described earlier, the daily iodine intake can be estimated from the urinary iodine concentration as follows:

  1. Median urine volume is 1.2 mL/hour/kg for a 10-year-old child (the median excretion rate for all children aged 7 to 15 years was 0.9 mL/hour/kg) (Mattsson and Lindstrom, 1995) and the median weight is 40 kg (Chapter 1); therefore the urine volume is about 1.15 L/day (1.2 × 40 × 24 hr).

  2. Approximately 92 percent of dietary iodine is excreted in the urine (Nath et al., 1992; Vought and London, 1967).

  3. Therefore, for a 10-year-old child weighing 40 kg, the urinary iodine concentration of 100 μg/L approximates a daily iodine intake of 125 μg (1.15 ÷ 0.92 × 100). This value suggests an RDA of approximately 125 μg/day.

Malvaux and coworkers (1969) conducted a balance study on 16 boys and girls (aged 9 to 13 years) in Belgium. The average iodine intake was 31 μg/day, and the average balance was –24 μg/day. This finding would suggest a minimum average requirement of approximately 55 μg/day (31 + 24).

The iodine requirement has not been determined based on energy expenditure; however, the thyroid hormones, which contain iodine, are involved with metabolic rate. Therefore, the EAR is extrapolated from adults by using metabolic body weight (kg0.75) and the method described in Chapter 2 to set an EAR at 73 μg/day.

Ages 14 through 18 Years. Malvaux and colleagues (1969) reported that the average iodine balance of 10 children (aged 14 to 16 years) was –24 μg/day when they consumed an average 34 μg/day of iodine, which would give 58 μg/day as an average requirement. No other data are available for estimating an average requirement for this age group. However, extrapolating down from adult data as described in Chapter 2 and using metabolic weight gives an EAR of 95 μg/ day, which is used to set the RDA as it is a higher estimate.

Iodine EAR and RDA Summary, Ages 1 through 18 Years

EAR for Children

 

1–3 years

65 μg/day of iodine

4–8 years

65 μg/day of iodine



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