Compartmental analyses of retinol kinetic data in animals has expanded our understanding of whole body vitamin A metabolism and stores. The approach has been recently applied to humans but few studies have used it to understand vitamin A metabolism in children because of the large number of blood samples required for the technique. However, the recent development of a super-child approach that limits the number of samples required of each individual child makes it possible to study vitamin A status in populations, compare metabolism between children and adults, and compare metabolism across populations. Ford and colleagues report the results of a study to determine retinol kinetics and total body vitamin A stores in children in the February 2020 issue of The Journal of Nutrition.
The subjects were young children from Bangladesh, Guatemala, and the Philippines. Ages of the children, vitamin A intake and receipt of high-dose vitamin A supplements varied among the countries. The children were provided with a dose of 13C-labeled retinyl acetate and blood samples were collected (1-2 per child) from 6 hours to 28 days after dosing.
Total body vitamin A stores predicted by the models were 198, 533 and 1062 µmol for children in Bangladesh (9-17 months), Philippines (12-18 months), and Guatemala (35-65 months). The kinetics of retinol metabolism were similar among children in the Philippines and Guatemala, but was faster in those from Bangladesh. Transfer of plasma retinol into the larger storage pool was similar among all three populations. However, retinol returned to plasma from the storage pool 2.5 times faster in Bangladeshi children. The composite tracer data set generated using samples from 5 children per time point led to sufficiently robust outcomes using the super child modeling approach to lead the authors to conclude that it was possible to determine total body vitamin A stores and retinol kinetics in children from different populations.
In a commentary on this article, Tanumihardjo points out the intriguing observation that retinol mobilization differs among children in the three countries, which adds support to the vitamin A relative dose rate as an effective tool for detecting vitamin A deficiency. However, if preformed vitamin A fortification occurs in the country, Tanumihardjo supports use of the retinal isotope dilution approach. Tanumihardjo also recommends use of the retinol isotope dilution technique to estimate average requirements and safe Recommended Daily Allowances for different age groups.
Reference Ford JL, Green JB, Haskell MJ, Ahmad SM, Cordero DIM, Oxley A, Engle-Stone R, Lietz G, Green MH. Use of model-based compartmental analysis and a super-child design to study whole-body retinol kinetics and vitamin A total body stores in children from 3 lower-income countries. The Journal of Nutrition, DOI: https://doi.org/10.1093/jn/nxz225.
Tanumihardjo SA. The dawn of a new era in vitamin A assessment. Journal of Nutrition, DOI: https://doi.org/10.1093/jn/nxz283.