TABLE 2.
Comparison of estimated TBS of vitamin A in US women by mathematical models of different study lengths and isotope dilution equations1
| Relative total traced mass to full compartmental model | |||
|---|---|---|---|
| Mean ± SD | Minimum, maximum | n | |
| Mathematical models | |||
| 14 d | 0.46 ± 0.26 | 0.21, 0.86 | 7 |
| 27 d | 0.63 ± 0.34 | 0.23, 1.31 | 7 |
| 52 (42–62) d | 0.87 ± 0.19 | 0.61, 1.09 | 5 |
| Full model2 | Reference | — | 7 |
| Isotope dilution equations | |||
| Modified Olson (Equation 1)3 | 0.49 ± 0.08 | 0.37, 0.60 | 7 |
| Short-term Olson (Equation 2)4 | 0.26 ± 0.09 | 0.14, 0.46 | 7 |
| Mass balance (Equation 3)5 | 1.23 ± 0.20 | 0.93, 1.46 | 7 |
Values were calculated as total traced mass or TBS of indicated model or equation/total traced mass from the full-length compartmental model. F, factor for efficiency of absorption and storage of a tracer dose in the liver; Fa, the fraction of the administered dose absorbed and in stores; S, ratio of specific activities or TTRs of retinol in serum to that in stores; SAp, “specific activity” (dose × 1/TTR) TBS, total body stores; TTR, tracer-to-tracee ratio.
One participant had her longest time point in the 52-d (42–62 d) category, which was used as her full model; therefore, she had no relative value for 52 d (42–62 d). The duration of the full model for this analysis was a median (quartile 1, quartile 3) of 122 d (110, 152 d).
Equation used was TBS = F × dose × S × H:D = 0.5 × 0.65 × dose × 1/(21 d TTR).
Equation used was TBS = Fa × S × (1/SAp) = 0.48 × dose × 1/(4 d TTR).
Equation used was TBS = factor for absorption × factor for catabolism × dose × 1/(21 d TTR) = 0.9 × 0.9 × dose ×1/(21 d TTR).