Vitamin A status (total body stores – TBS) can now be assessed using retinol isotope dilution (RID) and model-based compartmental analysis procedures. The model-based approaches require serial blood samples but also provide whole-body retinol kinetics in addition to TBS. The results of this approach are improved through the use of group-specific values for RID equation coefficients. It is difficult to obtain serial blood samples from children, and as such, a super-child approach has been developed that utilizes fewer samples from multiple subjects. These pooled sample approaches have been used to estimate vitamin A status in children from several countries, and work is ongoing to continue improving super-child sampling schemes. Lopez-Teros and colleagues have worked in this area and published the results of a new study in the June 2020 issue of The Journal of Nutrition.
Subjects for this study were 3-6 year-old children in Mexico, who were provided an oral dose of labeled retinyl acetate. Blood samples were collected at times from 8 to 21 days, and each child provided a sample on day 4, and on one other selected time point. A 6-compartment model was used to analyze the composite data to obtain group retinol kinetic parameters and pool sizes.
The TBS predicted from the model was 1097 µmol, and the TBS predicted using RID was 1096 µmol. The estimated TBS measured at day 4 was similar to values obtained at later sampling times. Retinol was predicted by the model to be in plasma for 1.5 hours during each transit and recycled into plasma 13 times before being utilized. The authors suggest that the super-child approach can be effectively used with RID to produce estimates of TBS using samples from any time between 4 and 21 days after the oral dose.
References Lopez-Teros V, Ford JL, Green MH, Monreal-Barraza B, Garcia-Miranda L, Tanumihardjo SA, Valencia ME, Astiazaran-Garcia H. The “Super-Child” approach is applied to estimate retinol kinetics and vitamin A total body stores in Mexican preschoolers. The Journal of Nutrition, Volume 150, Issue 6, June 2020, Pages 1644–1651, https://doi.org/10.1093/jn/nxaa048.
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