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breast milk of women who consumed low or high amounts of iodized salt was 143 or 270 μg/L, respectively (Gushurst et al., 1984), and within the range observed by Etling and coworkers (1986) and Johnson and coworkers (1990) (Table 8-1). The median concentration of iodine in human milk for all women was 146 μg/L for 14 days to 3.5 years postpartum. Based on an average milk excretion of 0.78 L/day (Chapter 2) and an average concentration of 146 μg/L, the mean amount of iodine secreted in human milk is 114 μg/day.

Iodine balance studies by Delange and coworkers (1984) showed that for full-term infants, aged 1 month and fed 20 μg/kg/day of iodine, total excretion was 12.7 μg/kg/day and iodine retention was 7.3 μg/kg/day. Thus, if the mean body weight at 6 months is 7 kg, then the infant in positive iodine balance excretes 90 μg/day.

Based on the median intake of iodine consumed from human milk and the average urinary iodine excretion of the infant, the AI for infants ages 0 through 6 months has been set at 110 μg/day.

Ages 7 though 12 Months. The AI for infants ages 7 through 12 months is 130 μg/day as determined by the method described in Chapter 2 to extrapolate from the younger infants. The AI for infants is greater than the Recommended Dietary Allowances (RDAs) for children and adolescents because the latter are based on extrapolation of adult data or on balance data for a specific age group (see “Children and Adolescents Ages 1 through 18 Years”).

TABLE 8-1 Iodine Concentration in Human Milk

Reference

Study Group

Stage of Lactation

Milk Iodine Concentration (μg/L)

Estimated Iodine Intakes of Infants (μg/d)a

Gushurst et al., 1984

24 women, 21–36 y

14 d–3.5 y

146

114

Etling et al., 1986

23 women, < 34 y

 

59

46

Johnson et al., 1990

14 women

< 2 mo

247

98

192

76

NOTE: Maternal intakes were not reported in these studies.

a Iodine intake based on reported data or concentration (μg/L) × 0.78 L/day.



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