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description, the conventional age intervals of the DRIs are used. Although requirement estimates have been developed for individual ages, these should be interpreted with care. Unsmoothed data have been used and year-by-year fluctuations may not be meaningful.

In addition to achieved size, it is necessary to estimate growth rates (weight velocities). After fitting linear regressions to median weights for segments of the age range, the regression slopes were taken as estimates of median weight velocities for the age interval. The estimates used are shown in Table 9-9.

Basal Losses. Basal iron loss estimates are based on the study of Green and coworkers (1968) (see “Selection of Indicators for Estimating the Requirement for IronFactorial Modeling”). Observations in adult men were extrapolated to adolescents on the basis of 14 mg/kg median weight and the losses for each age group are shown in Table 9-10.

Increase in Hemoglobin Mass. Estimation of the net iron utilization for increasing hemoglobin mass necessitates estimation of the rate of increase in blood volume and estimation of the rate of change in hemoglobin concentration. Blood volume is taken as approximately 75 mL/kg in boys and 66 mL/kg in girls (Hawkins, 1964). The average yearly weight gains for boys and girls are shown in Table 9-9. The rate of change in hemoglobin concentration has been directly estimated as the coefficients of the linear regression models applied to hemoglobin versus age for Nutrition Canada data by Beaton and coworkers (1989). The rate of change in hemoglobin concentration and the average hemoglobin concentrations for boys and girls are shown in Table 9-11. The iron content of hemoglobin is 3.39 mg/g (Smith and Rios, 1974), therefore the daily iron need for increased hemoglobin mass can be calculated as follows:

TABLE 9-9 Growth Velocity for Boys and Girls

Boys

Girls

Age (y)

(kg/y)

Age (y)

(kg/y)

9–12

4.87

9–11

4.77

13–14

10.43

12–13

7.24

15–17

2.75

14–17

1.63

18

0

18

0

 

SOURCE: Tanner et al. (1966).



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